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HlPPARCHUS IN THE OBSERVATORY OF ALEXANDRIA.
THE STORY
OF THE
SUN, MOON, AND STARS
BY
AGNES GIBERNE
Author of "The Starry Skies," "The World's Foundations, "Radiant Suns," Etc.
WITH COPIOUS ADDITIONS
FuTIg -ttluslrHieri
CINCINNATI
NATIONAL BOOK COMPANY
-A
23124
COPYRIGHT, 1898, BY J. T. JONES.
TWO COPIES REC i.VED.
INTRODUCTION.
By Charges Pritchard, M. A., F. R. S.,
Professor of Astronomy in the University of Oxford.
The pages of this volume on a great subject were submitted to my criticism while passing through the press, with a request from a friend that I would make any suggestions which might occur to me for its im- provement. Naturally, such a request was entertained, in the first instance, with hesitation and misgiving. But after a rapid perusal of the first sheet, I found my interest awakened, and then gradually secured ; for the book seemed to me to possess certain features of no ordinary character, and, in my judgment, held out the promise of supplying an undoubted want, thus en- abling me to answer a question which I have been often asked, and which had as often puzzled me, to the effect, " Can you tell me of any book on astron- omy suited to beginners ?" I think just such a book is here presented to the reader; for the tale of the stellar universe is therein told with great simplicity, and perhaps with sufficient completeness, in an ear- nest and pleasant style, equally free, I think, from in-
5
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6 INTRODUCTION.
accuracy or unpardonable exaggeration. We have here the outlines of elementary astronomy, not merely detailed without mathematics, but to a very great ex- tent expressed in untechnical language. Success in such an attempt I regard as a considerable feat, and one of much practical utility.
For the science of astronomy is essentially a science of great magnitude and great difficulty. From the time of Hipparchus, some century and a half before the Christian era, down to the present day, the culti- vation of astronomy has severely taxed the minds of a succession of men endowed with the rarest genius. The facts and the truths of the science thus secured have been of very slow accretion ; but like all other truths, when once secured and thoroughly understood, they are found to admit of very simple verbal expres- sion, and to lie well within the general comprehension, and, I may safely add, within the sympathies of all educated men and women.
Thus the great astronomers, the original discover- ers of the last twenty centuries, have labored, each in his separate field of the vast universe of nature, and other men, endowed with other gifts, have entered on their labors, and by systematizing, correlating, and simplifying the expression of their results, have brought the whole within the grasp of cultivated men engaged in other branches of the varied pursuits of our complicated life. It is in this sort of order
INTRODUCTION. 7
that the amelioration and civilization of mankind have proceeded, and at the present moment are, I hope and believe, rapidly proceeding.
It was, I suspect, under this point of view, though half unconsciously so, that my attention was arrested by the book now presented to the reader; for we have here many of the chief results of the laborious researches of such men as Ptolemy, Kepler, Newton, Herschel, Fraunhofer, Janssen, Lockyer, Schiapa- relli, and others — no matter where accumulated or by whom recorded — filtered through the mind of a thoughtful and cultured lady, and here presented to other minds in the very forms wherein they have been assimilated and pictured in her own. And these forms and pictures are true. It is in this way that the intel- lectual "protoplasm" of the human mind is fostered and practically disseminated.
And, then, there is still another point of view from which this general dissemination of great truths in a simple style assumes an aspect of practical impor- tance. I allude to the influences of this process on the imaginative or poetic side of our complex nature.
Wordsworth, in one of his prefaces, has stated so clearly the truth on this subject that I can not do bet- ter than give his words. "If the time should ever come," he says, "when what is now science becomes familiarized to men, then the remotest discoveries of the chemist, the botanist, the mineralogist, will be as
8 INTRODUCTION.
proper objects of the poet's art as any upon which it can be employed. He will be ready to follow the steps of the man of science; he will be at his side, carrying sensation into the midst of the objects of science itself. The poet will lend his divine spirit to aid the transfiguration, and will welcome the being thus produced as a dear and genuine inmate of the household of man."
It is for reasons such as here stated that I heartily commend this book to the attention of those who take an interest in the advancement of the intel- lectual progress and culture of society. The story of the Kosmos is told by the authoress in her own lan- guage and after her own method. I believe, as I have
said, the story is correct. Oxford University.
CONTENTS
Chapter. Page.
I. The Earth One of a Family, 13
II. The Head of Our Family, 24
III. What Binds the Family Together, ....... 34
IV. The Leading Members of Our Family. — First
Group, . 46
V. The Leading Members of Our Family. — Second
Group, 55
VI. The Moon, 62
VII. Visitors, 73
VIII. Little Servants, = 83
IX. Neighboring Families, .95
X. Our Neighbors' Movements, . . 106
XL More About the Solar System, 122
XII. More About the Sun, .133
XIII. Yet Morf About the Sun, 148
XIV. More About the Moon, 157
XV. Yet More About the Moon, 164
XVI. Mercury, Venus, and Mars, , . 180
XVII. Jupiter, . 199
XVIII. Saturn, 214
XIX. Uranus and Neptune, 225
XX. Comets and Meteorites, 240
XXI. More About Comets and Meteorites, 246
XXII. Many Suns, 267
9
IO CONTENTS.
Chapter. Page.
XXIII. Some Particular Suns, . . . . , . 278
XXIV. Different Kinds of Suns 291
XXV. Groups and Clusters of Suns, 304
XXVI. The Problem of Sun and Star Distances, . . .310
XXVII. Measurement of Star Distances, 320
XXVIII. The Milky Way, 329
XXIX. A Whirling Universe, 337
XXX. Reading the Light, 344
XXXI. Stellar Photography 355
XXXII. The Dawn of Astronomy, 363
XXXIII. Modern Astronomy, 375
XXXIV. Sir Isaac Newton, 382
XXXV. Later Astronomy, 393
LIST OF ILLUSTRATIONS.
Page.
Hipparchus in the Observatory at Alexandria Frontispiece.
The Solar System 15
The Pleiades 19
Sun-spots 29
Phases of Mercury before Inferior Conjunction — Evening Star 50
Appearance of the Full Moon 63
One Form of I,unar Crater 69
The Earth as Seen from the Moon 71
Passage of the Earth and the Moon through the Tail of a Comet 76
Passage of the Comet of 1843 Close to the Sun 79
Meteor Emerging from Behind a Cloud 84
The Great Shower of Shooting-stars, November 27, 1872 90
Constellation of the Great Bear 108
The Great Bear 50,000 Years Ago 109
The Great Bear 50,000 Years Hence 109
Constellation of Orion as it Appears Now no
Constellation of Orion 50,000 Years Hence in
Position of Planets Inferior to Jupiter — Showing the Zone of the
Asteroids 123
Comparative Size of the Planetary Worlds 130
A Typical Sun-spot 135
A Solar Eruption 138
Sun-flames, May 3, 1892 143
Solar Corona and Prominence 152
Comparative Size of the Earth and Sun 155
The Moon— an Expired Planet 159
The L,unar Crater Copernicus 170
I,unar Eruption— Brisk Action 172
Lunar Eruption — Feeble Action 173
Nicolaus Copernicus : 176
Phases of Venus 186
11
12 LIST OF ILLUSTRATIONS,.
Page.
Mars and the Path of its Satellites 191
General Aspect of Jupiter — Satellite and its Shadow 200
Satellites of Jupiter Compared with the Earth and Moon 206
The System of Jupiter 208
Orbits of Nine Comets Captured by Jupiter 213
Saturn and the Earth — Comparative Size 215
Ideal View of Saturn's Rings and Satellites from the Planet 222
Great Astronomers of Earlier Times , 227
The Great Comet of 1811 247
Donates Comet, 1858 249
Great Comet of 1744 254
The First Comet of 1888— June 4 255
Great Comet of 1680 260
Great Comet of 1769 261
Baron Alexander Von Humboldt 264
A Telescopic Field in the Milky Way 270
Cygnus, Constellation of 279
Stars whose Distances are Best Known 281
Lyra, Constellation of 297
Constellations in the Northern Hemisphere 300
A Cluster of Stars in Centaurus 305
The Great Nebula in Andromeda, Compared with Size of the Solar
System 307
A Cluster of Stars in Perseus 332
Hercules, Constellation of 338
The Great Bear, Constellation of 341
The Prism and Spectrum. . : 344
The Spectrocope 345
Spectra, Showing the Dark Lines 347
Great Astronomers of Later Times 377
Eye-piece of Lick Telescope 407
Lick Observatory 409
Professor E. E. Barnard 410
THE STORY
of thk
SUN, MOON, AND STARS.
CHAPTER I
THE EARTH ONE OF A FAMILY.
What is this earth, of ours?
Something very great — and yet something very little. Something very great, compared with the things npon the earth ; something very little, com- pared with the things outside the earth.
And as our journey ings together are for a while to be away from earth, we shall find ourselves obliged to count her as something quite small in the great universe, where so many larger and mightier things are to be found, — if indeed they are mightier. Not that we have to say good-bye altogether to our old home. We must linger about her for a while before starting, and afterwards it will be often needful to come back, with speed swifter than the flight of light, that we may compare notes on the sizes and condi- tions of other places visited by us.
But first of all: what is this earth of ours?
It was rather a pleasant notion which men held in olden days, that we — that great and important "We"
13
14 STORY OF THE SUN, MOON, AND STARS.
which loves to perch itself upon a height — stood firm and fixed at the very center of everything. The earth was supposed to be a vast flat plain, reaching nobody could tell how far. The sun rose and set for us alone ; and the thousands of stars twinkled in the sky at night for nobody's good except ours ; and the blue sky over- head was a crystal covering for the men of our earth, and nothing more. In fact, people seem to have counted themselves not merely to have had a kind of kingship over the lower animals of our earth, but to have been kings over the whole universe. Sun, stars, and sky, as well as earth, were made for man, and for man only.
This was the common belief, though even in those olden days there were some who knew better. But the world in general knows better now.
Earth the center of the universe ! Why, she is not that of even the particular family in the heavens to which she belongs. For we do not stand alone. The earth is one of a family of worlds, and that family is called The Solar System. And so far is our earth from being the head of the family, that she is not even one of the more important members. She is merely one of the little sisters, as it were.
Men not only believed the earth, in past days, to be at the center of the universe ; but also they believed her to remain there without change. Sun, moon, stars, planets, sky, might move ; but never the earth. The solid ground beneath their feet, that at least was firm. Every day the sun rose and set, and every night the stars, in like manner, rose and set. But this was easily explained. We on our great earth stood firm
THE EARTH ONE OF A FAMILY.
15
and still, while sun, moon, stars, went circling round us once in every twenty-four hours, just for our sole
THE SOI,AR SYSTEM.
and particular convenience. What an important per- sonage man must have felt himself then in God's great universe ! Once again, we know better now !
1 6 STORY OF THK SUN, MOON, AND STARS.
For it is the earth that moves, and not the sun; it is the earth that moves, and not the stars. The daily movements of sun and stars, rising in the east, travel- ing over the sky, and setting in the west, are no more real movements on their part than, when we travel in a railway-train, the seeming rush of hedges, telegraph posts, houses, and fields is real. They are fixed and we are moving ; yet the movement appears to us to be not ours but theirs.
Still more strongly would this appear to be the case if there were no noise, no shaking, no jarring and trembling, to make us feel that we are not at rest. Sometimes when a train begins to move gently out of a station, from among other trains, it is at the first moment quite impossible to say whether the move- ment belongs to the train in which we are seated or to a neighboring train. And in the motions of our earth there is no noise, no shaking, no jarring — all are rapid, silent, and even.
If you were rising through the air in a balloon, you would at first only know your own movement by see- ing the earth seem to drop away from beneath you. And just so we can only know the earth's movements by seeing how worlds around us seem to move in con- sequence.
When I speak of the Universe, I mean the whole of God's mighty creation as far as the stars reach. Some- times the word is used in this sense, and sometimes it is used only for a particular part of creation nearer to us than other parts. At present, however, we will put aside all thought of the second narrower meaning.
The wisest astronomer living can not tell us how
THE EARTH ONE OF A FAMILY. 1 7
far the stars reach. We know now that there is no firm crystal covering over onr heads, dotted with bright points here and there ; bnt only the wide open sky or heaven, containing millions of stars, some nearer, some farther, some bright enough to be seen by us all, some only visible through a telescope.
People talk often of the stars being "set in space;" and the meaning of " space " is simply "room." Where you are must be space, or you could not be there. But it is when we get away from earth, and travel in thought through the wide fields of space, where God has placed his stars, that we begin to feel how vast it is, and what specks we are ourselves— nay, what a speck our very earth is, in this great and boundless creation.
For there is no getting to the borders of space. As one telescope after another is made, each one stronger in power and able to reach farther than the last, still more and more stars are seen, and yet more and more behind and beyond, in countless millions.
It is the same all round the earth. The old notion about our world being a fiat plain has been long since given up. We know her now to be a round globe, not fixed, but floating like the stars in space.
When you look up into the sky, you are look- ing exactly in the opposite direction from where you would be looking up if you were in Australia. For Australia's "up" is our "down," and our "down" is Australia's "up." Or, to put it more truly, "up" is always in the direction straight away from this earth, on whatever part of it you may be standing; and "down " is always towards the center of the earth.
l8 STORY OF THE SUN, MOON, AND STARS.
All round the globe, in north, south, east, west, whether you are in Europe, Asia, Africa, or America, though you will see different stars in certain different quarters of the earth, still overhead you will find shin- ing countless points of light. , .
And now, what are these stars ? This is a matter on which people are often confused, and on which it is well to be quite clear beforegoing one step farther.
Some of the stars you have most likely often no- ticed. The seven chief stars of the Great Bear are known to a large number of people ; and there are few who have not admired the splendid constellation ot Orion. Perhaps you also know the W-shape of Cas- siopeia, and the brilliant shining of Sirius, and the soft glimmer of the Pleiades.
The different constellations or groups of principal stars have been watched by men for long ages past. They are called the fixed stars, for they do not change. How many thousands of years ago they were first ar- ranged by men into these groups, and who first gave them their names, we can not tell.
True, night by night, through century after cen- tury, they rise, and cross the sky, and set. But those are only seeming movements. Precisely as the turn- ing round of the earth upon her axis, once in every twenty-four hours, makes the sun appear to rise and cross the sky and set, in the day-time ; so also the same turning of the earth makes the stars appear to do the same in the night-time.
There is another seeming movement among the stars, which is only in seeming. Some come into
THE EARTH ONE OF A FAMILY.
19
view in summer which can not be seen in winter ; and some come into view in winter which can not be seen in summer. For the sun, moving on his pathway through the sky, hides those stars which shine with him in the day-time. The zodiac is an imaginary belt in the heavens, sixteen or eighteen degrees wide, containing the twelve constellations through which the sun passes. And as he passes from point to point of his pathway, he constantly conceals from us fresh groups of stars by day, and allows fresh groups to ap- pear by night. Speaking gen- erally, however, the stars remain the same year after year, cen- tury after centu- ry. The groups may still be seen as of old, fixed and unchanging. THE p^iades.
What are these stars? Stars and planets have both been spoken about. There is a great difference between the two.
Perhaps if you were asked whether the sun is most like to a star or a planet, you would be rather at a loss ; and many who have admired the brilliant evening star, Venus, often to be seen after sunset, would be surprised to learn that the evening star is in reality no star at all.
A star is a sun. Our sun is nothing more nor less than a star. Each one of the so-called " fixed stars,"
20 STORY OK THE SUN, MOON, AND STARS.
that you see shining at night in the sky, is a sun like our sun; only some of the stars are larger suns and some are smaller suns than ours.
The main reason why our sun looks so much larger and brighter than the stars is, that he is so very much nearer to us. The stars are one and all at enormous distances from the earth. By and by we will go more closely into the matter of their distance, compared with the distance of the sun.
At present it is enough to say that if many of the stars were placed just as near to us as our sun is placed, they would look just as large and bright; while there are some that would look a great deal larger and brighter. And if our sun were to travel away from us, to the distance of the very nearest of the little twinkling stars, he would dwindle down and down in size and brilliancy, till at last we should not be able to tell him apart from the rest of the stars.
I have told you that the stars are called " fixed " because they keep their places, and do not change from age to age. Though the movement of the earth makes them seem all to sweep past every night in company, yet they do not travel in and out among one another, or backwards and forwards, or from side to side. At all events, if there be such changes, they are so slow and so small as to be exceedingly difficult to find out. Each group of stars keeps its own old shape, as for hundreds of years back.
But among these fixed stars there are certain stars which do go to and fro, and backwards and forwards. Now they are to be seen in the middle of one constel-
THE EARTH ONE OF A FAMILY. 21
lation, and now in the middle of another. These rest- less stars were long a great perplexity. Men named them Planets or Wanderers.
We know now that the planets are in reality not stars at all, and also that they are not nearly so far away from us as the fixed stars. In fact, they are simply members of our own family — the Solar System. They are worlds, more or less like the world we live in; and they travel round and round the sun as we do, each more or less near to him; and they depend upon him for heat and light, in more or less the same manner as ourselves.
Therefore, just as our sun is a star, and stars are suns, so our earth or world is a planet, and planets are worlds. Earth is the name we give to that par- ticular world or planet on which we live. Planets may generally be known from stars by the fact that they do not twinkle. But the great difference be- tween the two lies in the fact that a star shines by its own radiant, burning light, whereas a planet shines merely by light reflected or borrowed from the sun.
But how were the earth and the other worlds made? Let us imagine an immense gaseous mass placed in space. Attraction is a force inherent in every atom of matter. The denser portion of this mass will insen- sibly attract towards it the other parts, and in the slow fall of the more distant molecules towards this more attractive region, a general motion is produced, in- completely directed towards this center, and soon in- volving the whole mass in the same motion of rota- tion. The simplest form of all, even in virtue of this law of attraction, is the spherical form. It is that
22 STORY OF THE SUN, MOON, AND STARS.
which a drop of water takes, and a drop of mercury if left to itself.
The laws of mechanics show that, as this gaseous mass condenses and shrinks, the motion of rotation of the nebula is accelerated. In turning, it becomes flattened at the poles, and gradually takes the form of an immense lens-shaped mass of gas. It has begun to turn so quickly as to develop at its exterior cir- cumference a centrifugal force superior to the general attraction of the mass, as when we whirl a sling. The inevitable consequence of this excess is a rupture of the equilibrium, which detaches an external ring. This gaseous ring will continue to rotate in the same time and with the same velocity; but the nebulous mother will be henceforth detached, and will continue to undergo progressive condensation and acceleration of motion. The same feat will be reproduced as often as the velocity of rotation surpasses that by which the centrifugal force remains inferior to the attraction. It may have happened also that secondary centers of condensation would be formed even in the interior of the nebula.
In our system the rings of Saturn still subsist.
The successive formation of the planets, their sit- uation near the plane of the solar equator, and their motions of translation round the same center, are ex- plained by the theory which we are discussing. The most distant known planet, Neptune, would be de- tached from the nebula at the epoch when this nebula extended as far as the planet, out to nearly three thou- sand millions of miles, and would turn in a slow revo- lution requiring a period of 165 years for its accom-
THE EARTH ONE OF A FAMILY. 23
plishment. The original ring could not remain in the state of a ring unless it was perfectly homogeneous and regular ; but such a condition is, so to say, unre- alizable, and it did not delay in condensing itself into a sphere. Successively, Uranus, Saturn, Jupiter, the army of small planets, Mars, would thus be detached or formed in the interior of this same nebula. After- wards came the earth, of which the birth goes back to the epoch when the sun had arrived at the earth's present position. Venus and Mercury would be born later. Will the sun give birth to a new world? This is not probable.
CHAPTER II.
THE HEAD OF OUR FAMILY.
PKOPLK began very early in trie history ot the world to pay close attention to the^ snn. And no wonder. We owe so much to his heat and light that the marvel would be if men had not thought much about him.
Was the sun really any larger than he looked, and if so, how much larger was he? And what was his distance from the earth? These were two of the ques- tions which puzzled our ancestors the longest. If once they could have settled exactly how far off the sun really was, they could easily have calculated his exact size; but this was just what they could not do.
So one man supposed that the sun must be quite near, and very little larger than he looked. Another thought he might be seventy-five miles in diameter. A third ventured to believe that he was larger than the country of Greece. A fourth was so bold as to imagine that he might even outweigh the earth herself.
After a while many attempts were made to measure the distance of the sun; and a great many different answers to this difficult question were given by differ- ent men, most of them very wide of the mark. It is only of late years that the matter has been clearly settled. And, indeed, it was found quite lately that a mistake of no less than three millions of miles had
24
THE HEAD OF OUR FAMILY. 25
been made, notwithstanding all the care and all the attention given. But though three millions of miles sounds a great deal, yet it is really very little — only a tiny portion of the whole.
For the distance of the sun from the earth is no less than about ninety-three millions of miles. Ninety-three millions of miles ! Can you picture that to yourself? Try to think what is meant by a thou- sand miles. Our earth is eight thousand miles in diameter. In other words, if you were to thrust a gigantic knitting-needle through her body, from the North Pole to the South Pole, it would have to be about eight thousand miles long.
To reach the thought of one million, you must pic- ture one thousand times one thousand. Our earth is about twenty-five thousand miles round. It you were to start from the mouth of the River Amazon, in South America, and journey straight round the whole earth on the equator, till you came back to the same point, you would have traveled about twenty-five thousand miles. But that would be a long way off from a million miles. You would have gone only once round the earth. Now a cord one million miles in length could be wrapped, not once only, but forty ttmesy round and round the earth. And when you have managed to reach up to the thought of one million miles, you have then to remember that the sun's distance is ninety- three times as much again. So, to picture clearly to ourselves the actual meaning of " ninety- three mil- lions of miles' ' is not so easy.
Suppose it were possible to lay a railroad from here to the sun. If you could journey thither in a per-
26 STORY OF THE SUN, MOON, AND STARS.
fectly straight line, at the rate of thirty miles an hour, never pausing for one single minute, night or day, you would reach the sun in about three hundred and forty- six years.
Thirty miles an hour is a slow train. Suppose we double the speed, and make it an express train, rush- ing along at the pace of sixty miles an hour. Then you might hope to reach the end of your journey in one hundred and seventy-three years. If you had quitted this earth early in the eighteenth century, never stopping on your way, you would be, just about now, near the end of the nineteenth, arriving at the sun.
So much for the sun's distance from us. Now as to his size.
I have already mentioned that our earth's diameter — that is, her through measure, as, for instance, the line drawn straight from England through her center to New Zealand — is about eight thousand miles. This sounds a good deal. But what do you think of the diameter of the sun being no less than eight hundred and fifty -eight thousand miles f The one is eight thou- sand miles, the other over eight hundred thousand !
Suppose you had a long slender pole which would pass through the middle of the earth, one end just showing at the North Pole and the other at the South Pole. You would need more than a hundred and eight of such poles, all joined together, to show the diameter of the sun.
The sun seems not to be made of nearly such heavy materials as the earth. He is what astronomers call less " dense," less close and compact in his make, just as wood is less dense and heavy than iron. Still, his
THE HKAD OF OUR FAMILY. 27
size is so enormous, that if you could have a pair of gigantic scales, and put the sun into one scale and the earth with every one of her brother and sister planets into the other, the sun's side would go down like lightning. He would be found to weigh seven hundred and fifty times as much as all the rest put together. And, it would take more than twelve hun- dred thousand little earths like ours, rolled into one huge ball, to make a globe as large as the sun.
In the beginning of the seventeenth century a man named Fabricius was startled by the sight of a certain black spot upon the face of the sun. He watched till too dazzled to look any longer, supposing it to be a small cloud, yet anxious to learn more. Next day the spot was there still, but it seemed to have moved on a little way. Morning after morning this move- ment was found to continue, and soon a second spot, and then a third spot, were observed creeping in like man- ner across the sun. After a while they vanished, one at a time, round his edge, as it were ; but after some days of patient waiting on the part of the lookers-on, they appeared again at the opposite edge, and once more began their journey across.
Fabricius seems to have been the first, but he was not the last, to watch sun-spots. Many astronomers have given close attention to them. Modern tele- scopes, and the modern plan of looking at the sun through darkened glass, have made this possible in a way that was not possible two or three hundred years ago.
The first important discovery made through the spots on the sun, was that the sun turns round upon
28 STORY OF THE SUN, MOON, AND STARS.
his axis, just in the same manner that the earth turns round upon hers. Instead of doing' so once in the course of each twenty-four hours, like the earth, he turns once in the course of about twenty-five days.
It must not be supposed that the spots seen now upon the sun are the same spots that Fabricius saw so long ago. There is perpetual change going on; new spots forming, old spots vanishing; one spot break- ing into two, two spots joining into one, and so on. Even in a single hour great alterations are sometimes seen to take place.
Still, many of the spots do remain long enough and keep their shapes closely enough to be watched from day to day, and to be known again as old friends when they reappear, after being about twelve days hidden on the other side of the sun. So that the turning of the sun upon his axis has become, after long and care- ful examination, a certain known fact.
For more than thirty years one astronomer kept close watch over the spots on every day that it was possible to see the sun. Much has been learned from his resolute perseverance.
Now what are these spots ?
One thing seems pretty sure, and that is that they are caused by some kind of tremendous storms or cyclones taking place on the surface of that huge ball of fire.
The first attentive observer of the sun, Scheiner, at first regarded the spots as satellites— an indefensi- ble opinion, which, however, some have attempted to revive. Galileo attributed them to clouds or vapors floating in the solar atmosphere; this was the best
THB HEAD OF OUR FAMILY.
29
conclusion which could be drawn from the observa- tions of that epoch. This opinion met for a long time with general approval ; it has even been renewed in our day. Some astronomers, and among them
SUN SPOTS.
Lalande, believed, on the contrary, that they were mountains, of which the flanks, more or less steep, might produce the aspect of the penumbra — an opin- ion irreconcilable with the proper motion which the spots sometimes possess in a very marked manner. It is not usual, in fact, to see mountains traveling.
3o
Derham attributed them to the smoke issuing from the volcanic craters of the sun, an opinion revived and maintained in recent times by Chacornac. Several savants, regarding the sun as a liquid and incandescent mass, have also explained the spots [by immense cin- ders floating on this ocean of fire. But a century had scarcely elapsed after the epoch when the spots were observed for the first time, when an English astron- omer, Wilson, showed with certainty that the spots are hollow.
We do not know with any certainty whether the sun is through and through one mass of glowing mol- ten heat, or whether he may have a solid and even cool body within the blazing covering. Some have thought the one, and some the other. We only know that he is a mighty furnace of heat and flame, beyond anything that we can possibly imagine on our quiet little earth.
It seems very sure that no such thing as " quietness " is to be found on the surface of the sun. The wildest and fiercest turmoil of rushing wind and roaring flame there prevails. The cyclones or hurricanes which take place are sometimes so rapid and so tremendous in extent, tearing open the blazing envelope of the sun, and showing glimpses of fiery though darker depths below, that we, on our far-distant earth, can actually watch their progress.
Astronomers speak of the " quivering fringe of fire " all around the edge of the sun, visible through tele- scopes. But the sun is perpetually turning on his axis, so that each hour fresh portions of his surface thus pass the edge, showing the same appearance.
THE HEAD OF OUR FAMILY. 3 1
What conclusion can we come to but that the whole enormous surface of the sun is one restless, billowy sea of fire and flame?
It sounds to us both grand and startling to hear of the mighty outbreaks from Mount Vesuvius, or to read of glowing lava from a volcano in Hawaii pouring in one unbroken stream for miles.
But what shall be thought of rosy flames mounting to a height of fifty or a hundred thousand miles above the edge of the sun? What shall be thought of a tongue of fire long enough to fold three or four times round our solid earth? What shall be thought of the awful rush of burning gases, sometimes seen, borne along at the rate of one or two or even three hundred miles in a single second across the sun's surface? What shall be thought of the huge dark rents in this raging fiery ocean, rents commonly from fifty to one hundred thousand miles across, and not seldom more?
Fifty thousand miles ! A mere speck, scarcely visible without a telescope; yet large enough to hold seven earths like ours flung in together. The largest spot measured was so enormous that eighteen earths might have been arranged in a row across the breadth of it, like huge boulders of rock in a mountain cavern; and to have filled up the entire hole about one hundred earths would have been needed.
It is well to grow familiar with certain names given by astronomers to certain parts of the sum
The round shining disk or flat surface, seen by all of us, is called the photosphere, or "light-sphere." It has a tolerably well-defined edge or "limb," and daz- zles the eye with its intense brightness.
32 STORY OF THE SUN, MOON, AND STARS.
Across the photosphere the spots move, sometimes many, sometimes few, in number. Besides the dark spots, there are spots of extreme brilliancy, standing out on even that dazzling surface, which causes a piece of white-hot iron to look black and cold by contrast. These extra-radiant spots which come and go, and at times change with great rapidity, are named faculce — a Latin word meaning " torches."
At the edge of the photosphere astronomers see what has been already mentioned, that which is some- times called the chromotosphere, which one has named "the sierra^ and which another has described as "a quivering fringe of fire." The waves of the sea, on a stormy day, seen in the distance rising and breaking the horizon-line, may serve as an illustration ; only in the sun the waves are of fire, not water. What must their height be, to be thus visible at a distance of ninety- three millions of miles ?
Outside the sierra are seen, at certain seasons, bright, "rose-colored prominences " or flames of enor- mous height. During an eclipse, when the dark body of the moon comes between the sun and us, exactly covering the photosphere, these red tips stand out distinctly beyond the edge of sun and moon. Their changes have been watched, and their height repeat- edly measured. Some are so lofty that ten little earths such as ours might be heaped up, one upon another, without reaching to their top. Whether they are in character at all like the outbursts from our own vol- canoes it is hard to say. To compare the two would be rather like comparing a small kitchen fire with a mighty iron-smelting furnace. The faculse, the
THE HEAD OE OUR FAMILY. 33
sierra, and the prominences are visible only through a telescope.
Outside these red flames or " prominences " is the corona, commonly divided into the inner and outer coronas.
Many different explanations have been offered of this beautiful crown of light round the sun, plainly visible to the naked eye during an eclipse. But here again we know little, and must be content to watch and wait. 3
CHAPTER III.
WHAT BINDS THE FAMILY TOGETHER?
What is it which binds together all the members of the Solar System? Ah, what? Why should not the sun at any moment rush away in one direction, the earth in a second, the planets in half a dozen others? What is there to hinder such a catastrophe? Nothing — except that they are all held together by a certain close family tie; or, more correctly, by the powerful influence of the head of the family.
This mysterious power which the sun has, and which all the planets have also in their smaller de- grees, is called Attraction. Sometimes it is named Gravitation or Gravity. When we speak, as we often do, of the law of attraction or gravitation, we mean simply this — that throughout the universe, in things little and great, is found a certain wonderful some- thing, in constant action, which we call a " law." What the "something" may be, man can not tell; for he knows it only by its effects. But these effects are seen everywhere, on all sides, in the earth and in the universe. It is well named in being called a "law;" for we are compelled to obey it. None but the Divine Lawgiver who made this law can for a sin- gle moment suspend its working.
What causes an apple to fall to the ground when it drops from the branch? Why should it not, instead, rise upwards? Because, of course, it is heavy, or has
34
WHAT BINDS THE FAMILY TOGETHER. 35
weight. But what is weight? Simply this- — that the earth draws or drags everything downwards towards herself by the power of attraction. Every substance, great or small, light or heavy, is made up of tiny atoms. Each one of these atoms attracts or draws all the other atoms towards itself; and the closer they are together, the more strongly they pull one another.
The atoms in a piece of iron are much closer than the atoms in a piece of. wood ; therefore the iron is called the "more dense" of the two, and its weight or " mass " is greater. The more closely the atoms are pressed together, the greater the number of them in a small space, and the more strong the drawing to- wards the earth ; for the earth draws each one of these atoms equally. That is only another way of saying that a thing is " heavier." If you drop a stone from the top of a cliff, will it rise upwards or float in the air? No, indeed. The pull of the earth's attraction, dragging and still dragging downward, makes it rush through the air, with speed quickening each instant, till it strikes the ground. Every single atom in every single body pulls every other atom, whether far or near. The nearer it is, the stronger always the pulling.
We do not always feel this, because the very much greater attraction of the earth hides — or smothers, as we may say — the lesser attraction of each small thing for another. But though you and I might stand side by side upon earth, and feel no mutual attraction, yet if we could mount up a few thousands of miles, far away from earth, and float in distant space, there we
36 STORY OF THE SUN, MOON, AND STARS.
should find ourselves drawn together, and unable to remain apart.
Now precisely as an apple falling from a tree and a stone dropping from a cliff are dragged downward to the earth, just so our earth and all the planets are dragged downwards towards the sun and towards each other. The law of the earths attraction of all objects on its surface to itself was indistinctly suspected a very long time ago; but it was the great Newton who first discovered that this same law was to be found working among the members of the whole Solar Sys- tem. The sun attracts the earth, and the earth at- tracts the sun. But the enormous size of the sun compared with our earth — like a great nine-foot globe beside a tiny one-inch ball — makes our power of at- traction to be quite lost sight of in his, which is so much greater.
The principle of gravitation is of far wider scope than we have yet indicated. We have spoken merely of the attraction of the earth, and we have stated that its attraction extends throughout space. But the law of gravitation is not so limited. Not only does the earth attract every other body, and every other body attract the earth, but each of these bodies attracts each other; so that, in its more complete shape, the law of gravitation announces that " every body in the universe attracts every other body with a force which varies inversely as the square of the distance." It is impossible for us to overestimate the importance of this law. It supplies the clue by which we can un- ravel the complicated movements of the planets. It has led to marvelous discoveries, in which the law of
WHAT BINDS THE FAMILY TOGETHER. 37
gravitation has enabled us to anticipate the telescope, and, indeed, actually to feel the existence of bodies before those bodies have even been seen.
We come now to another question. If the sun is pulling with such power at the earth and all her sis- ter planets, why do they not fall down upon him? What is to prevent their rolling some day into one of those deep rents in his fiery envelope? Did you ever tie a ball to a string, and swing it rapidly round and round your head? If you did, you must have noticed the steady outward pull of the ball. The heavier the ball, and the more rapid its whirl, the stronger the pull will be. Let the string slip, and the rush of the ball through the air to the side of the room will make this yet more plain. Did you ever carry a glass of water quickly along, and then, on suddenly turning a corner, find that the water has not turned with you? It has gone on in its former direction, leaving the glass, and spilling itself on the floor.
The cause in both cases is the same. Here is an- other "law of nature, " so-called. Though we can neither explain nor understand why and how it is so, we see it to be one of the fixed rules of God's working in every-day life throughout his universe. The law, as we see it, seems to be this : Everything which is at rest must remain at rest, until set moving by some cause outside of, or independent of itself; and every- thing which is once set moving, must continue moving in a straight line until checked.
According to this a cannon-ball lying on the ground ought to remain there until it is set in motion ; and, once set in motion by being fired from a cannon, it ought
38 STORY OF THE SUN, MOON, AND STARS.
to go on forever. Exactly so — if nothing stops it. But the earth's attraction draws the cannon-ball down- ward, and every time it strikes the ground it is partly checked. Also each particle of air that touches it helps to bring it to rest. If there were no earth and no air in the question, the cannon-ball might rush on in space for thousands of years.
Why did the water get spilled ? Because it neces- sarily continued moving in a straight line. Your sud- den change of direction compelled the solid glass to make the same change, but the liquid water was free to go straight on in its former course ; so it obeyed this law, and did go on. Why did the ball pull hard at the string as you swung it round ? Because at each in- stant it was striving to obey this same law, and to rush onward in a straight line. The pull of the string was every moment fighting against that inclination, and forcing the ball to move in a circle.
Just such is the earth's movement in her yearly journey round the sun. The string holding in the ball pictures the sun's attraction holding in the earth. The pulling of the ball outward in order to continue its course in a straight line, pictures the pulling of our earth each moment to break loose from the sun's attraction and to flee away into distant space.
For the earth is not at rest. Each tick of the clock she has sped onward over more than eighteen miles of her pathway through the sky. Every instant the sun is dragging, with the tremendous force of his at- traction, to make her fall nearer to him. Every in- stant the earth is dragging with the tremendous force of her rapid rush, to get away from him. These two
WHAT BINDS THE FAMILY TOGETHER. 39
pullings so far balance each other, or, more strictly, so far combine together, that between the two she jour- neys steadily round and round in her nearly circular orbit.
If the sun pulled a little harder she would need to travel a little faster, or she would gradually go nearer to him. If the earth went faster, and the sun's at- traction remained the same as it is now, she would gradually widen her distance. Indeed, it would only be needful for the earth to quicken her pace to about five-and-twenty miles a second, the sun's power to draw her being unchanged, and she would then wander away from him for ever. Day by day we on our earth should travel farther and farther away, leav- ing behind us all light, all heat, all life, and finding ourselves slowly lost in darkness, cold, and death.
For what should we do without the sun? All our light, all our warmth, come from him. Without the sun, life could not exist on the earth. Plants, herbage, trees, would wither ; the waters of rivers, lakes, oceans, would turn to masses of ice ; animals and men would die. Our earth would soon be one vast, cold, forsaken tomb of darkness and desolation.
We may not think so, but everything which moves, circulates, and lives on our planet is the child of the sun. The most nutritious foods come from the sun. The wood which warms us in winter is, again, the sun in fragments. Every cubic inch, every pound of wood, is formed by the power of the sun. The mill which turns under the impulse of wind or water, revolves only by the sun. And in the black night, under the rain or snow, the blind and noisy train, which darts
4-0 STORY OF THE) SUN, MOON, AND STARS.
like a flying serpent through the fields, rushes along above the valleys, is swallowed up under the mountains, goes hissing past the stations, of which the pale eyes strike silently through the mist, — in the midst of night and cold, this modern animal, produced by human in- dustry, is still a child of the sun. The coal from the earth which feeds its stomach is solar work, stored up during millions of years in the geological strata of the globe.
As it is certain that the force which sets the watch in motion is derived from the hand which has wound it, so it is certain that all terrestrial power proceeds from the sun. It is its heat which maintains the three states of bodies — -solid, liquid, and gaseous. The last two would vanish, there would be nothing but solids ; water and air itself would be in massive blocks, — if the solar heat did not maintain them in the fluid state. It is the sun which blows in the air, which flows in the water, which moans in the tempest, which sings in the unwearied throat of the nightingale. It at- taches to the sides of the mountains the sources of the rivers and glaciers, and consequently the cataracts and the avalanches are precipitated with an energy which they draw directly from him. Thunder and lightning are in their turn a manifestation of his power. Every fire which burns and every flame which shines has re- ceived its life from the sun. And when two armies are hurled together with a crash, each charge of cav- alry, each shock between two army corps, is nothing else but the misuse of mechanical force from the same star. The sun comes to us in the form of heat, he leaves us in the form of heat; but between his ar-
WHAT BINDS THE FAMILY TOGETHER. 41
rival and his departure, he has given birth to the varied powers of our globe.
I have spoken before about the old-world notion that our earth was a fixed plain, with the sun circling round her. When the truth dawned slowly upon some great minds, anxious only to know what really was the truth, others made a hard struggle for the older and pleasanter mode of thinking. It went with many sorely against the grain to give up all idea of the earth being the chief place in the universe. Also there was something bewildering and dizzying in the notion that our solid world is never for one moment still. But truth won the victory at last. Men con- sented slowly to give up the past dream, and to learn the new lesson put before them.
We still talk of the sun rising and setting, and of the stars doing the same. This is, however, merely a common form of speech, which means just the oppo- site. For instead of the sun and stars moving, it is the earth which moves.
The earth has two distinct movements. Indeed, I ought to say that she has three ; but we will leave all thought of the third for the present. First, she turns round upon her axis once in every twenty-four hours. Secondly, she travels round the sun once in about every three hundred and sixty-five days and a quarter. No wonder our ancestors were startled to learn that the world, which they had counted so immovable, was per- petually spinning like a humming-top, and rushing through space like an arrow.
You may gain some clear notions as to the daily rising and setting of our sun, with the help of an
43 STORY OF THF, SUN, MOON, AND STARS.
orange. Pass a slender knitting-needle through the orange, from end to end, and hold it about a yard dis- tant from a single candle in a room otherwise darkened. Let the needle or axis slant somewhat, and turn the orange slowly upon it.
The candle does not move ; but as the orange turns, the candle-light falls in sucession upon each portion of the yellow rind. Half of the orange is always in shade, and half is always in light ; while at either side, if a small fly were standing there, he would be passing round out of shade into candle-light, or out of candle- light into shade.
Bach spot on our earth moves round in turn into half-light, full-light, half-light, and darkness; or, in other words, has morning-dawn, midday-light, evening twilight, and night. Each spot on our earth would undergo regularly these changes every twenty-four hours throughout the year, were it not for another arrangement which so far affects this that the North and South Poles are, by turns, cut off from the light during many months together.
Thus the sun is in the center of the Solar System, turning slowly on his axis; and the earth and the planets travel round him, each spinning like a teeto- tum, so as to make the most of his bright warm rays. But for this spinning movement of the earth, our day and night, instead of being each a few hours long, would each last six months.
You may notice that, as you turn the orange steadily round, the outside surface of the skin has to move much more slowly in those parts close to the knitting- needle, than in those parts which bulge out farthest
WHAT BINDS THE FAMILY TOGETHER. 43
from it. Near trie North and South Poles the surface of our earth travels slowly round a very small circle in the course of twenty-four hours. But at the equator every piece of ground has to travel about twenty-five thousand miles in the same time ; so that it rushes along at the rate of more than one thousand miles an hour. A man standing on the earth at the equator is being carried along at this great speed, not through the air, for the whole atmosphere partakes of the same rapid motion, but with the air, round and round the earth's axis.
Now about the other movement of the earth — her yearly journey round the sun. While she moves, the sun, as seen from the earth, seems to change his place. First he is observed against a background of one group of stars, then against a second, then against a third. Not that the stars are visible in the daytime when the sun is shining, but their places are well known in the heavens; and also they can be noted very soon after he sets, or before he rises, so that the constella- tions nearest to hirn may each day be easily found out.
Of course, in old times the sun was thought to be really taking this journey among the stars, and men talked of " the sun's path " in the heavens. This path was named "the Ecliptic," and we use the word still, though we know well that the movements are not really his, but ours.
As the earth's daily movement causes day and night, so the earth's yearly movement causes spring, summer, autumn, and winter. A few pages back I mentioned, in passing, one slight yet important fact which lies at the root of this matter about the seasons. The earth,
44 STORY OF THF, SUN, MOON, AND STARS.
journeying round the sun, travels with her axis slant- ing. Put your candle in the middle of the table, and stand at one end, holding your orange. Now let the knitting-needle, with the orange upon it, so slant that one end shall point straight over the candle, towards the upper part of the wall at the farther end of the room. Call the upper end so pointing the North Pole of your orange. You will see that the candle-light falls chiefly upon the upper half of the orange ; and as you turn it slowly, to picture day and night, you will find that the North Pole has no night, and the South Pole has no day. That is summer in the northern hemisphere, and winter in the southern.
Walk round next to one side of the table, towards the right hand, taking care to let the knitting-needle point steadily still in exactly the same direction, not towards the same spot, for that would alter its direction as you move, but towards the same wall. Stop, and you will find the candle lighting up one-half of your orange, from the North to the South Poles. Turn it slowly, never altering the slope of the axis, and you will see that every part of the orange comes by turns under the light. This is the Autumnal Equinox, when days and nights all over the world are equal in length.
Walk on to the other end of the table, still letting the needle slope and point steadily as before. Now the candle-light will shine upon the lower or South Pole, and the North Pole will be entirely in the shade. This is summer in the southern hemisphere, and winter in the northern.
Pass on to the fourth side of the table, and once
WHAT BINDS THB FAMILY TOGETHER. 45
more you will find it, as at the second side, equal light from North Pole to South Pole. This will be the Spring Equinox.
It is an illustration that may be easily practiced. Bug everything depends upon keeping the slant of the needle or r.::is unchanged throughout. If it be allowed to point first to right, and then to left, first towards the ceiling, i/nd then towards the wall, the attempt will prove a failure.
CHAPTER IV.
THE LEADING MEMBERS OF OUR FAMILY— FIRST GROUP.
The chief distinction between stars and planets is, as before said, that the stars shine entirely by their own light, while the planets shine chiefly, if not entirely, by reflected light. The stars are snns; mighty globes of glowing flame. The planets simply receive the light of the snn, and shine with a brightness not their own.
A lamp shines by its own light ; bnt a looking-glass, set in the sun's rays and flashing beams in all direc- tions, shines by reflected light. In a dark room it would be dark. If there were no sun to shine upon Mars or Venus, we should see no brightness in them. The moon is like the planets in this. She has only bor- rowed light to give, and none of her own.
Any one of the planets removed to the distance of the nearest fixed star, would be invisible to us. Re- flected light will not shine nearly so far as the direct light of a burning body. There may be thousands or millions of planets circling round the stars — those great and distant suns — just as our brother-planets circle round our sun. But it is impossible for us to see them. The planets which we can see are close neighbors, compared with the stars. I do not mean that they are near in the sense in which we speak of nearness upon earth. They are only near in compari- son with what is so very much farther away.
46
LEADING MEMBERS OF OUR FAMILY. 47
For a while we must now leave alone all thought of the distant stars, and try to gain a clear idea of the chief members of our own Family Circle — that family circle of which the sun is the head, the center, the source of life and warmth and light. There are two ways in which astronomers group the planets of the Solar System. One way is to divide them into the Inferior Planets, and the Superior Planets.
As the earth travels in her pathway round the sun, two planets travel on their pathways round the sun nearer to him than ourselves. If the pathway or orbit of our earth were pictured by a hoop laid upon the table, with a ball in the center for the sun; then those two planets would have two smaller hoops of different sizes within ours; and the rest would have larger hoops of different sizes outside ours. The two within are called inferior planets, and the rest outside are called superior planets.
A round hoop would not make a good picture of an orbit. For the yearly pathway of our earth is not in shape perfectly round, but slightly oval; and the sun is not exactly in the center, but a little to one side of the center. This is more or less the case with the orbits of all the planets.
But the laying of the hoops upon the table would give no bad idea of the way in which the orbits really lie in the heavens. The orbits of all the chief planets do not slope and slant round the sun in all manner of directions. They are placed almost in the same plane as it is called — or, as we might say, in the same flat. In these orbits the planets all travel round in the same direction. One may overtake a second on a neighbor-
48 STORY OF THE SUN, MOON, AND STARS.
ing orbit, and get ahead of him, but one planet never goes back to meet another.
In speaking of the orbits, I do not mean that the planets have visible marked pathways through the heavens, any more than a swallow has a visible path- way through the sky, or a ship a marked pathway through the sea. Yet each planet has his own orbit, and each planet so distinctly keeps to his own, that astronomers can tell us precisely whereabouts in the heavens any particular planet will be, at any particu- lar time, long years beforehand.
There is also another mode of grouping the planets, besides dividing them into superior and inferior plan- ets. By this other mode we find two principal groups or quartets of planets, separated by a zone or belt of a great many very small planets.
( Mercury.
«"* G™P \ SrtK
t Mars.
The Asteroids or Planetoids. C Jupiter.
Second Group \*g^
C Neptune.
The first four are small compared with the last four, though much larger than any in the belt of tiny Asteroids.
It was believed at one time that a planet had been discovered nearer to the sun than Mercury, and the name Vulcan was given to it. But no more has been seen of Vulcan, and his existence is so doubtful that we must not count him as a member of the family without further information.
LEADING MEMBERS OE OUR FAMILY. 49
Mercury is very much smaller than our Earth. The diameter of the earth is eight thousand miles, but the diameter of Mercury is only about three thousand miles — not even half that of the earth. Being so much nearer to the sun than ourselves, the pulling of his attraction is much greater, and this has to be bal- anced by greater speed, or Mercury would soon fall down upon the sun. Our distance from the sun is ninety- three millions of miles. Mercury's distance is only about one-third of ours ; and instead of traveling, like the earth, at the rate of eighteen miles each second, Mercury dashes headlong through space at the mad pace of twenty-nine miles each second. It is a good thing the earth does not follow his example, or she would soon break loose from the sun's control alto- gether.
The earth takes more than three hundred and sixty- five days, or twelve months, to journey round the sun in her orbit. That is what we call " the length of our year." But Mercury's year is only eighty-eight days, or not quite three of our months. No wonder ! — when his pathway is so much shorter, and his speed so much greater than ours. So Mercury has four years to one year on earth; and a person who had lived on Mer- cury as long as five earthly years, would then be twenty years old. The increased number of birthdays would scarcely be welcome in large families, suppos- ing we could pay a long visit there.
The sun, as seen from Mercury, looks about four and a half times as large as from here ; the heat and glare being increased in proportion. No moon has ever been found, belonging to Mercury.
50 STORY OF the; sun, moon, and stars.
The planet Mercury is, like the earth and the moon, a globe of dark matter which only shines and is visi- ble by the illumination of the solar light. Its motion round the central star, which brings it sometimes be- tween the sun and us, sometimes in an oblique direc- tion, sometimes at right angles, and shows us a part incessantly variable, of its illuminated hemisphere, produces in its aspect, as seen in a telescope, a suc- cession of phases similar to those which the moon
PHASES OF MERCURY BEFORE INFERIOR CONJUNCTION — EVENING
STAR.
presents to us. The cut represent the apparent varia- tions of size and the succession of phases, visible in the evening after sunset; when the planet attains its most slender crescent, it is in the region of its orbit nearest to the earth, and passes between the sun and us ; then, some weeks afterwards, it emerges from the solar rays and passes again through the same series of phases in inverse order, as we see them by revers- ing the figure.
Venus, the second inferior planet, is nearly the same size as our earth. Seen from the earth, she is one of the most brilliant and beautiful of all the planets.
LEADING MEMBERS OE OUR FAMILY. 51
Her speed is three miles a second faster than ours, and her distance from the sun is about two-thirds that of our own ; so that the orbit of Venus lies half- way between the orbit of Mercury and the orbit of the earth. The day of Venus is about half an hour shorter than ours. Her year is nearly two hun- dred and twenty-five days, or seven and a half of our months. One or two astronomers have fancied that they caught glimpses of a moon near Venus ; but this is still quite doubtful, and indeed it is believed to have been a mistake.
Venus and Mercury are only visible as morning and evening planets. Venus, being farther from the sun, does not go before and follow after him quite so closely as Mercury, and she is therefore the longer within sight.
When Venus, traveling on her orbit, comes just between the sun and us, her dark side is turned to- wards the earth, and we can catch no glimpse of her. When she reaches that part of her orbit which is farthest from us, quite on the other side of the sun, her great distance from us makes her light seem less. But about half-way round on either side, she shows exceeding brilliancy, and that is the best view we can get of her.
Seen through a telescope, Venus undergoes phases like those of Mercury, or of our moon. That is to say, we really have "new Venus," "quarter Venus," "half Venus," "full Venus," and so on.
Of all the luminaries in the heavens, the sun and moon excepted, the planet Venus is the most conspic- uous and splendid. She appears like a brilliant lamp
52
amid the lesser orbs of night, and alternately antici- pates the morning dawn, and nshers in the evening twilight. When she is to the westward of the snn, in winter, she cheers our mornings with her vivid light, and is a prelude to the near approach of the break of day and the rising sun. When she is eastward of that luminary, her light bursts upon us after sunset, before any of the other radiant orbs of heaven make their appearance; and she discharges, in some measure, the functions of the absent moon. The brilliancy of this planet has been noticed in all ages, and has been fre- quently the subject of description and admiration both by shepherds and by poets. The Greek poets distin- guished it by the name of Phosphor, "light-bringer," when it rose before the sun, and Hesperus, "the west," when it appeared in the evening after the sun retired. It is now generally distinguished by the name of the Morning and Evening Star.
Next to the orbit of Venus comes the orbit of our own Earth, the third planet of the first group.
Mars, the fourth of the inner quartet, but the first of the superior planets, is a good deal smaller than Venus or the earth. The name Mars, from the heathen god of war, was given on account of his fiery reddish color. Mars is better placed than Venus for being observed from earth. When he is at the nearest point of his orbit to us, we see him full in the blaze of sun- light ; whereas Venus, at her nearest point, turns her bright face away.
The length of the day of Mars — or, in other words, the time he takes to turn upon his axis- — is only forty minutes longer than that of earth. Mars' journey
SHADING MEMBERS OF OUR FAMILY. 53
round the sun is completed in the course of six hun- dred and eighty-seven days, not much less than two of our years. His distance from the sun is about one hundred and forty millions of miles, and his speed is fourteen miles a second. We shall find, with the in- creasing distance of each planet, that the slower pace balances the lessened amount of the sun's attraction.
Passing on from Mars, the last of the first group of planets, we reach the belt of Asteroids, sometimes called Planetoids, Minor Planets, or Telescopic Planets. They are so tiny that Mercury is a giant compared with the largest among them.
The zone of space containing all these little planets is more than a hundred millions of miles broad. Their orbits do not lie flat in almost the same plane, but slant about variously in a very entangled fashion. If a neat model were made of this zone, with a slender piece of wire to represent each orbit, it would be found impossible to lift up one wire without pulling up all the rest with it. Those asteroids lying nearest to the sun take about three of our years to travel round him, and those lying farthest take about six of our years.
New members of the group are very often found. The number of asteroids now known amounts to about three hundred and twenty. Ceres is estimated by Professor Barnard, of the Yerkes Observatory, Chi- cago University, to be six hundred miles in diameter. Vesta is about two hundred and fifty miles in diameter. Meta, on the other hand, is less than seventy-five miles. There are some smaller ones that do not measure twenty miles in diameter, and it is probable
54 STORY OF THE SUN, MOON, AND STARS.
that there are many which are so small as to be ab- solutely invisible to the best telescopes, and which measure only a few hundred rods in diameter. Twenty thousand Vestas would be needed to make one globe equal to our earth in size.
Are they worlds? Why not? Is not a drop of water, shown in the microscope, peopled with a mul- titude of various beings? Does not a stone in a meadow hide a world of swarming insects? Is not the leaf of a plant a world for the species which in- habit and prey upon it? Doubtless among the mul- titude of small planets there are those which must remain desert and sterile, because the conditions of life (of any kind) are not found united. But we can not doubt that on the majority the ever-active forces of nature have produced, as in our world, creations appropriate to these minute planets. L,et us repeat, moreover, that for nature there is neither great nor little. And there is no necessity to natter ourselves with a supreme disdain for these little worlds ; for in reality the inhabitants of Jupiter would have more right to despise us than we have to despise Vesta, Ceres, Pallas, or Juno. The disparity is greater be- tween Jupiter and the earth than between the earth and these planets. A world of two, three, or four hundred miles in diameter is still a continent worthy to satisfy the ambition of a Xerxes or a Tamer- lane.
CHAPTER V.
THE LEADING MEMBERS OF OUR FAMILY— SECOND GROUP.
Leaving behind us the busy zone of planetoids, hurrying round and round the sun in company, we cross a wide gap, and come upon a very different sight.
The distance from the sun which we have now reached is little less than four hundred and fifty mil- lions of miles, or about five times as much as the earth's distance; and the sun in the heavens shows a diameter only one-fifth of that which we are accus- tomed to see. Slowly — yet not slowly — floating on- wards through space, in his far-off orbit, we find the magnificent planet Jupiter.
Is eight miles each second slow progress? Com- pared with the wild whirl of little Mercury, or even compared with the rate of our own earth's advance, we may count it so ; but certainly not, compared with our notions of speed upon earth. Bight miles each second is five hundred times as fast as the swiftest ex- press-train^ ever made by man. No mean pace that for so enormous a body. For Jupiter is the very largest of all the members of the Solar System except the sun himself — quite the eldest brother of the fam- ily. His diameter is about eighty-five thousand miles, his axis being nearly eleven times as long as that of earth. Though in proportion to his great bulk not
55
56 STORY OF THE SUN, MOON, AND STARS.
nearly so heavy as our earth, yet his bulk is so vast that more than twelve hundred earths would be needed to make one Jupiter.
It must not, however, be forgotten that there is a certain amount of uncertainty about these measure- ments of Jupiter. He seems to be so covered with a dense atmosphere and heavy clouds that it is quite impossible for us to learn the exact size of the solid body within.
Jupiter does not travel alone. Borne onwards with him, and circling steadily around him, are five moons; the smallest with a probable diameter of about one hun- dred miles ; one about the same size as our own moon, and the others all larger. The nearest of the five, though distant from the center of the planet over one hundred and twelve thousand miles, revolves about him in twelve hours ; the second, though farther from Jupiter than our moon from the earth, speeds round him in less than two of our days. The most distant, though over a million miles away, takes scarcely seven- teen days to accomplish its long journey. Jupiter and his moons make a little system by themselves — a family circle within a family circle.
Like the smaller planets, Jupiter spins upon his axis ; and he does this so rapidly that, notwithstanding his great size, his day lasts only ten hours, instead of twenty-four hours like ours. But if Jupiter's day is short, his year is not. Nearly twelve of our years pass by before Jupiter has traveled once completely round the sun. So a native of earth who had just reached his thirty -seventh year, would, on Jupiter, be only three years old.
LEADING MEMBERS OE OUR EAMIEY. 57
Passing onward from Jupiter, ever farther and farther from the sun, we leave behind us another vast and empty space — empty as we count emptiness, though it may be that there is in reality no such thing as emptiness throughout the length and breadth of the universe. The width of the gap which divides the pathway of Jupiter from the pathway of his giant brother-planet Saturn is nearly five times as much as the width of the gap separating the earth from the sun. The distance of Saturn from the sun is cot much less than double the distance of Jupiter.
With this great space in our rear, we come upon another large and radiant planet, the center, like Ju- piter, of another little system ; though it can only be called "little" in comparison with the much greater Solar System of which it forms a part.
Saturn's diameter is less than that of Jupiter, but the two come near enough to be naturally ranked to- gether. Nearly seven hundred earths would be needed to make one globe as large as Saturn. But here again the dense and cloudy envelope makes us very uncertain about the planet's actual size. Saturn is like Jupiter in being made of lighter materials than our earth; and also in his rapid whirl upon his axis, the length of his "day" being only ten and a half of our hours.
From Jupiter's speed of eight miles each second, we come down in the case of Saturn to only five miles each second. And Jupiter's long annual journey looks almost short, seen beside Saturn's long journey of thirty earthly years. A man aged sixty, according to our fashion of reckoning time, would on Saturn have just kept his second birthday.
5»
The system or family of Saturn is yet more won- derful than that of Jupiter. Not five only but eight moons travel ceaselessly round Saturn, each in its own orbit; and in addition to the eight moons, he has revolving round him three magnificent rings. These rings, as well as the moons, shine, not by their own brilliancy, for they have none, but by borrowed sun- light. The farthest of the moons wanders in his lonely pathway about two millions of miles away from Saturn. The largest of them is believed to be about the same size as the planet Mars. Of the three rings circling round Saturn, almost exactly over his equator, the inside one is dusky, purplish, and transparent ; the one outside or over that is very brilliant; and the third, outside the second, is rather grayish in hue.
Another vast gap — more enormous than the last. It is a wearisome journey. From the orbit of Jupiter to the orbit of Saturn at their nearest points, was five times as much as from the sun to the earth. But from the orbit of Saturn to the orbit of Uranus, the next member of the sun's family, we have double even that great space to cross.
Still, obedient to the pulling of the sun's attractive power, Uranus wanders onward in his wide pathway round the sun, at the rate of four miles a second. Kighty-four of our years make one year of Uranus. This planet has four moons, and thus forms a third smaller system within the Solar System ; but he may have other satellites also, as yet undiscovered. In size he is seventy-four times as large as our earth.
One more mighty chasm of nine hundred millions of miles, for the same distance which separates the
LEADING MEMBERS OE OUR FAMILY. 59
pathway of Saturn from the pathway of Uranus, sep- arates also the pathway of Uranus from the pathway of Neptune. Cold, and dark, and dreary indeed seems to us the orbit on which this banished member of our family circle creeps round the sun, in the course of one hundred and sixty-five years, at the sluggish rate of three miles a second.
On the planet Saturn, the quantity of light and heat received from the sun is not much more than a hundredth part of that which we are accustomed to receive on earth. But by the time we reach Neptune, the great sun has faded and shrunk in the distance until to our eyes he looks only like an exceedingly brilliant and dazzling star.
We know little of this far-off brother, Neptune, except that he is rather larger than Uranus, being one hundred and five times as big as the earth; that he has at least one moon; and also that, like Uranus, he is made of materials lighter than those of earth, but heavier than those of Jupiter or Saturn.
After all, it is no easy matter to gain clear ideas as to sizes and distances from mere statements of "so many miles in diameter," and "so many millions of miles away." A "million miles" carries to the mind a very dim notion of the actual reality.
Now if we can in imagination bring down all the members of the Solar System to a small size, keeping always the same proportions, we may find it a help. "Keeping the same proportions" means that all must be lessened alike, all must be altered in the same degree. Whatever the supposed size of the earth may be, Venus must be still about the same size as the
60 STORY OF THE SUN, MOON, AND STARS.
earth, Saturn seven hundred times as large, and so on, Also, whatever the distance of the earth from the sun, in miles, or yards, or inches, Mercury must still be one- third as far, Jupiter still five times as far, and thus with the rest.
First, as to size alone. Suppose the earth is repre- sented by a small globe, exactly three inches in diam- eter. It will be a very small globe. Not only men and houses, but mountains, valleys, seas, will all have to be reduced to so minute a size, as to be quite invisi- ble to the naked eye.
Fairly to picture the other members of the Solar System, in due proportion, you will have them as follows :
Mercury and Mars will be balls smaller than the earth, and Venus nearly the same size of the earth. Uranus and Neptune will be each somewhere about a foot in diameter. Saturn will be twenty-eight inches and Jupiter thirty-two inches in diameter. The sun will be a huge dazzling globe, twenty-six feet in di- ameter. No wonder he weighs seven hundred and fifty times as much as all his planets put together.
Next let us picture the system more exactly on another and smaller scale. First, think of the sun as a brilliant globe, about nine feet, or three yards, in diameter, floating in space.
About one hundred yards from the sun travels a tiny ball, not half an inch in diameter, passing slowly round the sun — slowly, because as sizes and distances are lessened, speed must in due proportion be lessened also. This is Mercury. About two hundred yards from the sun travels another tiny ball, one inch in di-
LEADING MEMBERS OF OUR FAMILY. 6l
ameter. This is Venus. Nearly a quarter of a mile from the sun travels a third tiny ball, one inch again in diameter; and at a distance of two feet and a half from it a still smaller ball, one quarter of an inch in diameter, journeys round it and with it. These are the earth and the moon. About half as far again as the last-named ball, travels another, over half an inch in diameter. This is Mars.
Then comes a wide blank space, followed by a large number of minute objects, no bigger than grains of powder, floating round the sun in company. These are the Asteroids. Another wide blank space suc- ceeds the outermost of them.
About one mile distant from the sun journeys a globe, ten inches in diameter. Round him, as he journeys, there travel five smaller balls, the largest of which is about the third of an inch in diameter. Their distances from the bigger globe vary from one and a third to twelve and a half feet. These are Jupiter and his moons.
Nearly two miles distant from the sun journeys another globe, about eight and a half inches in diam- eter. Eight tiny balls and three delicate rings circle round him as he moves. These are Saturn and his belongings. About four miles distant from the sun journeys another globe, four inches in diameter, with four tiny balls accompanying him — Uranus and his moons. Lastly, at a distance of six miles from the sun, one more globe, not much larger than the last, with one tiny companion, pursues his far-off pathway.
These proportions as to size and distance will serve to give a clear idea of the Solar System.
CHAPTER VI.
THE MOON.
Come, and let us pay a visit to the moon. We seem to feel a personal interest in her, just because she is, in so peculiar a sense, our own friend and close attendant. The sun shines for us ; but, then, he shines for all the members of the Solar System. And the stars — so many as we can see of them — shine for us too; but no doubt they shine far more brilliantly for other and nearer worlds. The moon alone seems to belong especially to ourselves.
Indeed, we are quite in the habit of speaking about her as "our moon." Rather a cold and calm friend, some may think her, sailing always serenely past, whatever may be going on beneath her beams; yet she has certainly proved herself constant and faithful in her attachment.
We have not very far to travel before reaching her, — merely about two hundred and forty thousand miles. That is nothing, compared with the weary millions of miles which we have had to cross to visit some mem- bers of our family. A rope two hundred and forty thousand miles long would fold nearly ten times round the earth at the equator. You know the earth's di- ameter— about eight thousand miles. If you had thirty poles, each eight thousand miles long, and could fasten them all together, end to end, one beyond another, you would have a rod long enough to reach from the earth to the moon.
62
THE MOON.
63
Let us take a good look at her before starting. She is very beautiful. That soft silvery light, so unlike sunlight or gaslight, or any other kind of light seen upon earth, has made her the darling of poets and the delight of all who love nature. Little children like to watch her curious markings, and to make out
APPEARANCE OF THE) FUU, MOON.
the old man with his bundle of sticks, or the eyes, nose, and mouth of the moon — not dreaming what those markings really are. And in moods of sadness, how the pure calm moonlight seems to soothe the feelings ! Who would suppose that the moon's beauty is the beauty rather of death than of life ?
The stars have not much chance of shining through her bright rays. It is well for astronomers that she is not always at the full. But when she is, how large she looks — qvtite as large as the sun, though in reality
64 STORY OF THE SUN, MOON, AND STARS.
her size, compared with, his, is only as a very small pin's head compared with a school globe two feet in diameter. Her diameter is little more than two thou- sand miles, or one quatrer that of our earth; and her whole surface, spread out flat, would scarcely equal North and South America, without any of the sur- rounding islands.
The reason she looks the same size as the sun, is that she is so very much nearer. The sun's distance from us is more than one-third as many millions of miles as the moon's distance is thousands of miles. This makes an enormous difference.
We call our friend a " moon," and say that she journeys round the earth, while the earth journeys round the sun. This is true, but it is only part of the truth. Just as certainly as the earth travels round the sun, so the moon also travels round the sun. And just as surely as the earth is a planet, so the moon also is a planet. It is a common mode of expression to talk about " the earth and her satellite." A no less correct, if not more correct, way would be to talk of ourselves as "a pair of planets," journeying round the same sun, each pulled strongly towards him, and each pulling the other with a greater or less attraction, ac- cording to her size and weight. For the sun actually does draw the moon with more force than that with which the earth draws her. Only as he draws the earth with the same sort of force, and nearly in the same degree, he does not pull them apart.
The moon, like the other planets, turns upon her axis. She does this very slowly, however; and most singularly she takes exactly the same time to turn
THK MOON. 65
once upon her axis that she does to travel once round the earth. The result of this is, that we only see one face of the moon. If she turned upon her axis, and journeyed round the earth in two different lengths of time, or if she journeyed round us and did not turn upon her axis at all, we should have views of her on all sides, as of other planets. But as her two move- ments so curiously agree, it happens that we always have one side of the moon towards us, and never catch a glimpse of the other side.
And now we are ready to start on our journey of two hundred and forty thousand miles. An express train, moving ceaselessly onward night and day, at the rate of sixty miles an hour, would take us there in about five months and a half. But no line of rails has ever yet been laid from the earth to the moon, and no " Flying Dutchman " has ever yet plied its way to and fro on that path through the heavens. Not on the wings of steam, but on the wings of imagination, we must rise aloft. Come — it will not take us long. We shall pass no planets or stars on the road, for the moon lies nearer to us than any other of the larger heavenly bodies.
Far, far behind us lies the earth, and beneath our feet, as we descend, stretch the broad tracts of moon- land. For " downward" now means towards the moon, and away from the distant earth.
What a strange place we have reached! The weird, ghastly stillness of all around, and the glaring, daz- zling, cloudless heat, strike us first and most forcibly. Nothing like this heat have we ever felt on earth. For the close of the moon's long day — on this side of its 5
66 STORY OF TH3 SUN, MOON, AND STARS.
globe — is approaching, and during a whole fortnight past the sun's fierce rays have been beating down on these shelterless plains. Talk of sweltering tropics on earth! What do you call this heat? Look at the thermometer : how the quicksilver is rising ! Well, that is not a common thermometer which we have brought with us. The mercury has stopped — three hundred degrees above boiling water!
Not a cloud to be seen overhead ; only a sky of inky blackness, with a blazing sun, and thousands of brill- iant stars, and the dark body of our own earth, large and motionless, and rimmed with light. Seen from earth, sun and moon look much the same size; but seen from the moon, the earth looks thirteen times as large as our full moon. Not even a little mistiness in the air to soften this fearful glare ! Air ! why, there is no air ; at least not enough for any human being to breathe or feel. If there were air, the sky would be blue, not black, and the stars would be invisible in the daytime. It looks strange to see them now shining beside the sun.
And then, this deadly stillness! Not a sound, not a voice, not a murmur of breeze or water. How could there be ? Sound can not be carried without air, and of air there is none. As for breeze — wind is moving air, and where we have no air we can have no wind. As for water — if there ever was any water on the moon, it has entirely disappeared. We shall walk to and fro vainly in search of it now. No rivers, no rills, no torrents in those stern mountain ramparts rising on every side. All is craggy, motionless, desolate.
How very, very slowly the sun creeps over the black
THE MOON. 6j
sky! And no marvel, since a fortnight of earth-time is here bnt one day, answering to twelve hours upon earth. Can not we find shelter somewhere from this blazing heat? Yonder tall rock will do, casting a sharp shadow of intense blackness. We never saw such shadows upon earth. There the atmosphere so breaks and bends and scatters about the light, that outlines of shadows are soft and hazy, even the clearest and darkest of them, compared with this.
When will the sun go down? But he is well worth looking at meanwhile. How magnificent he appears, with his pure radiant photosphere, fringed by a sierra of dazzling pink and white, orange and gold, purple and blue. For here no atmosphere lies between to blend all into yellow-white brightness. And how plainly stand out those prominences or tongues of tinted flame, not merely rose-colored, as seen from earth, but matching the sierra in varying hues ; while beyond spreads a gorgeous belt of pink and green, bounded by lines and streams of delicate white light, reaching far and dying slowly out against the jet back- ground. The black spots on the face of the sun are very distinct, and so also are the brilliant faculae.
We must take a look around us now at moonland, and not only sit gazing at the sun, though such a sky may well enchain attention. How unlike our earthly landscapes! No sea, no rivers, no lakes, no streams, no brooks, no trees, bushes, plants, grass, or flowers; no wind or breeze ; no cloud or mist or thought of pos- sible rain; no sound of bird or insect, of rustling leaves or trickling water. Nothing but burning, stead- fast, changeless glare, contrasting with inky shadows;
68 STORY OF THE SUN, MOON, AND STARS.
sun and earth and stars in a black heaven above; silent, desolate mountains and plains below.
For though we stand here upon a rough plain, this moon is a mountainous world. Ranges of rugged hills stretch away in the distance, with valleys lying between — not soft, green, sloping, earthly valleys, but steep gorges and precipitous hollows, all white dazzle and deep shade.
But the mountains do not commonly lie in long ranges, as on earth. The surface of the moon seems to be dented with strange round pits, or craters, of every imaginable size. We had a bird's-eye view of them as we descended at the end of our long journey moonward. In many parts the ground appears to be quite honeycombed with them. Here are small ones near at hand, and larger ones in the distance. The smaller craters are surrounded by steep ramparts of rock, the larger ones by circular mountain-ranges. We have nothing quite like them on earth.
Are they volcanoes? So it would seem; only no life, no fire, no action, remain now. All is dead, motionless, still. Is this verily a blasted world ? Has it fallen under the breath of Almighty wrath, com- ing out scorched and seared ? Is it simply passing through a certain burnt-out, chilled phase of existence, through which other planets also pass, or will pass, at some stage of their career? Who can tell?
We will move onward, and look more closely at that towering mass of rugged rocks, beyond which the sun will by and by go down. Long jetty shadows lie from them in this direction. No wonder astronomers on earth can through their telescopes plainly see these
THE MOON.
69
black shadows contrasting with the glaring brightness on the other side.
A "mass of rocks" I have said; but as, with our powers of rapid movement, we draw near, we find a range of craggy mountains sweeping round in a vast circle. Such a height in Switzerland would demand many hours of hard climbing. But on this small globe attraction
is a very differ- ent matter from what it is on earth; our weight is so lessened that we can leap the height of a tall house with- out the smallest difficulty. No chamois ever sprang from peak to peak in his native Switzerland with such amazing lightness as that with which we now ascend these mighty rocks. Ha! what a depth on the other side! We stand looking down into one of the monster craters of the moon. A sheer descent of at least eleven thousand feet would land us at the bottom. Why, Mont Blanc itself is only about fifteen thousand feet in height. And what a crater ! Fifty-six miles across in a straight line, from here to the other side, with these lofty rugged battlements circling round, while from the center of the rough plain below a sharp, cone-shaped
ONE FORM OP I,UNAR CRATER.
JO STORY OF THE SUN, MOON, AND STARS.
mountain rises to about a quarter of the height of the surrounding range.
It is a grand sight; peak piled upon peak, crag upon crag, sharp rifts or valleys breaking here and there the line of the narrow, uplifted ledge ; all wrapped in silent and desolate calm. There are many such craters as this on the moon, and some much larger.
The sun slowly nears his setting, and sinks behind the opposite range. How we shiver ! The last ray of sunlight has gone and already the ground is pouring out its heat into space, unchecked by the presence of air or clouds. The change takes place with marvelous quickness. A deadly chill creeps over all around. A whole fortnight of earth-time must pass before the sun's rays will again touch this spot. Verily the con- trasts of climate in the moon, during the twelve long days and nights which make up her year, are startling to human notions.
But though the sun is gone we are not in darkness. The stars shine with dazzling brightness, and the huge body of the earth, always seeming to hang motionless at one fixed point in the sky, gives brilliant light, though at present only half her face is lit up and half is in shadow. Still her shape is plainly to be seen, for she has ever round her a ring of light, caused by the gathered shining of stars as they pass behind her thick atmosphere. She covers a space on the sky more than a dozen times as large as that covered by the full moon in our sky.
It would be worth while to stay here and watch the half-earth grow into magnificent full-earth. But the cold is becoming fearful — too intense for even the
THE EARTH AS SEEN FROM THE MOON,
7i
72 STORY OF THE SUN, MOON, AND STARS.
imagination to endure longer. What must be the state of things on the other side of the moon, where there is no bright earth-light to take the place of the sun's shining, during the long two weeks' night of awful chill and darkness?
It seems probable that a building on the moon would remain for century after century just as it was left by the builders. There need be no glass in the windows, for there is no wind and no rain to keep out. There need not be fireplaces in the rooms, for fuel can not burn without air. Dwellers in a city in the moon would find that no dust can rise, no odors be perceived, no sounds be heard. Man is a creature adapted for life in circumstances which are very nar- rowly limited. A few degrees of temperature, more or less ; a slight variation in the composition of air, the precise suitability of food, make all the difference between health and sickness, between life and death. Looking beyond the moon, into the length and breadth of the universe, we find countless celestial globes, with every conceivable variety of temperature and of con- stitution. Amid this vast number of worlds with which space teems, are there any inhabited by living beings ? To this great question science can make no response save this: We can not tell.
Time for us to wend our way homewards from this desolate hundred-fold arctic scene. We have more to learn by and by about our friend and companion. For the present — enough.
CHAPTER VII.
VISITORS.
WE come next to the very largest members of our Solar System.
From time to time in past days — and days not very long past either — people were startled by the sight of a long-tailed star, moving quickly across the sky, called a comet. We see such long-tailed stars still, now and then; but their appearance no longer startles us.
It is hardly surprising, however, that fears were once felt. The great size and brilliancy of some of these comets naturally caused large ideas to be held as to their weight, and the general uncertainty about their movements naturally added to the mysterious notions afloat with respect to their power of doing harm.
A collision between the earth and a comet seemed no unlikely event; and if it happened — what then? Why, then, of course, the earth would be overpowered, crushed, burnt up, destroyed. So convinced were many on this point that the sight of a comet and the dread of the coming "end of the world" were fast bound together in their minds.
Even when astronomers began to understand the paths of some of the comets, and to foretell their re- turn at certain dates, the old fear was not quickly laid to rest. So late as the beginning of the present cen-
73
74 STORY OF THE SUN, MOON, AND STARS.
tury, astronomers having told of an approaching comet, other people added the tidings of an approach- ing collision. "If a collision, then the end of the world, " was the cry; and one worthy family, living and keeping a shop in a well-known town on the south coast of England, packed up and fled to Amer- ica— doubtless under full belief that the destruction of the Old World would not include the destruction of the New.
The nature of these singular bodies is somewhat better known in the present day ; yet even now, among all the members of the Solar System, they are perhaps the ones about which we have most to learn. The nucleus, or bright and star-like spot, which, with the surrounding coma or "hair," we sometimes call the "head" of the comet, is the densest and heaviest part of the whole. The comets are of immense size, some- times actually filling more space than the sun him- self, and their tails stream often for millions of miles behind them ; nevertheless, they appear to be among the lightest of the members of the Solar System.
This excessive lightness greatly lessens the comet's power of harm-doing. In the rebound from all the old exaggerated fears, men laughed at the notion of so light and delicate a substance working any injury whatever, and even declared that a collision might take place without people on earth being aware of the fact. It is now felt that we really know too little about the nature of the said substance to be able to say what might or might not be the result of a col- lision. A certain amount of injury to the surface of the earth might possibly take place. But of the
visitors. 75
" end of the world," as likely to be brought about by any comet in existence, we may safely banish all idea.
The word "comet" means "a hairy body," the name having been given from the hairy appearance of the light around the nucleus. About seventeen hundred different comets have been seen at different times by men — some large, some small ; some visible to the naked eye, but most of them only visible through telescopes. These hundreds are, there is no doubt, but a very small number out of the myriads ranging through the heavens.
If you were seated in a little boat in mid-ocean, counting the number of fishes which in one hour passed near enough in the clear water for your sight to reach them, you might fairly conclude, even if you did not know the fact, that for every single fish which you could see, there were tens of thousands which you could not see.
Reasoning thus about the comets, as we watch them from our earth-boat in the ocean of space, we feel little doubt that for each one which we can see, millions pass to and fro beyond reach of our vision. Indeed, so long ago as the days of Kepler, that great astronomer gave it as his belief that the comets in the Solar System, large and small, were as plentiful as the fishes in the sea. And all that modern as- tronomers can discover only tends to strengthen this view.
Why should the comets be called "visitors?" I call them so simply because many of them are visitors. Some, it is true, belong to the Solar System. But
76 STORY OF THE SUN, MOON, AND STARS.
even in their case, strong donbts are felt whether they were not once visitors from a distance, caught in the first instance by the attraction of one of the larger planets, and retained thenceforward, for a time at least, by the strong attraction of the sun.
Every comet, like every planet, has his own orbit or pathway in the heavens, though the kind of orbit
PASSAGE OF THE EARTH AND THE MOON THROUGH THE TAII, OF A
COMET.
varies with different comets. There are, first, those comets which travel round and round the sun in "closed orbits" — that is, in a ring with joined ends. Only the ring is always oval, not round. There are, secondly, those which travel in an orbit which may be closed; but if so, the oval is so long and narrow, and the farther closed end is at so great a distance, that we can not speak certainly. There are, thirdly, those which decidedly are mere visitors. They come from the far-off star-depths, flash once with their brilliant trains of light through our busy Solar System, causing
VISITORS. J7
some little excitement by the way, and go off in an- other direction, never to return.
Only a small part of the orbits of these comets can be seen from earth ; but by careful attention astrono- mers learn something of the shape of the curve in which they travel. It is in that way possible to cal- culate, sometimes certainly, and sometimes uncer- tainly, whether a comet may be expected to return, or whether we have seen him for the first and the last time. By looking at part of a curve, the rest of which is hidden from us, we are able to judge whether that part belongs to a circle or an oval, or whether the two ends pass away in different direc- tions, and do not join.
The comets, whether members of our family circle or visitors from a distance, are altogether very perplex- ing. They are often extremely large, yet they are al- ways extremely light. They reflect the sun's bright- ness like a planet, yet in some measure they seem to shine by their own light, like a star. They obey the attraction of the sun, yet he appears to have a singu- lar power of driving the comets' tails away from himself.
For, however rapidly the comet may be rushing round the sun, and however long the tail may be, it is almost always found to stream in an opposite direction from the sun. An exception to this rule was seen in the case of a certain comet with two tails, one of which did actually point towards the sun ; but the in- ner tail may have been only a " jet" of unusual length, like in kind to the smaller jets often thus poured out from the nucleus.
yS STORY OF THE SUN, MOON, AND STARS.
Very curious changes take place in comets as they journey, especially as they come near the sun. One was seen in the course of a few days to lose all his hair, and also his tail. Another was seen to break into two pieces, both of which pieces at last disap- peared. Sometimes the one tail divides into two tails.
Traveling, as the comets do, from intense cold into burning heat, they are very much affected by the vio- lent change of climate. For the paths of the comets are such long ovals, or ellipses, that, while they ap- proach the sun very closely in one part of their "year," they travel to enormous distances in the other part.
" Halley's Comet," which takes seventy-six of our years to journey round the sun, comes nearer to him than Venus, and goes farther away from him than Neptune. As this comet draws gradually closer, he has to make up for the added pull of the sun's in- creasing attraction by rushing onward with greater and greater rapidity, till he whirls madly past the sun, and then, with slowly slackening speed, journeys far- ther and farther away, creeps at length lazily round the farther end of his orbit in the chill, dark, neigh- borhood of Neptune, and once more travels towards the sun with growing haste.
"Encke's Comet" has a year of only three and a half of our years, so he may be said to live quite in our midst. But many comets travel much farther away than the one named after Halley. It is calcu- lated of some that, if they ever return at all, it can not be for many hundreds of years.
11 Newton's Comet," seen about two centuries ago, has a journey to perform of such length that he is
VISITORS.
79
not expected again to appear for several thousand years. Yet, at the nearest point in his orbit, he ap- proached the sun so closely, that the heat which he
PASSAGE OF THE COMET OF 1843 CLOSE TO THE SUN (FEBRUARY 27TH, IO HOURS, 29 MINUTES.)
endured was about two thousand times that of red- hot iron. Changes were seen to be taking place in his shape, as he drew near to the sun, and disappeared. Four days he was hidden in the sun's rays. He van- ished, with a tail streaming millions of miles behind
80 STORY OF THE SUN, MOON, AND STARS.
him. He made his appearance again with a tail streaming millions of miles in front of him. Bnt how this wonderful movement took place is beyond man's power to explain.
The comet of 1843 was one of the most attractive seen during the present century. It was first observed in March, and it appeared with a suddenness which had quite a startling effect. It was an imposing object in the southern regions. The comet was seen in Italy on the 28th of February; at Washington, on the 6th of March ; at Oporto, on the 14th ; but owing to unfa- vorable weather, it was not visible in England, or any of the northern countries of Europe, previous to the 17th. A little after sunset on that day the tail was observed in the western sky, but the head had already sunk below the horizon. The whole of the comet ap- peared on the following evenings for a short time, for it was traveling away from the sun with great veloc- ity, having doubled the solar orb before it became visible; and about the beginning of April it finally disappeared.
The appearance of this startling stranger, as ob- served at Washington, is thus described by Lieuten- ant Maury, of the Hydrographical Office in that city: uOn Monday morning, March 6th, our attention was called to a paragraph in the newspapers, stating that a comet was visible near the sun at midday with the naked eye. The sky was clear; but not being able to discover any thing with the unassisted eye, recourse was had to the telescope, but with no better success. About sunset in the evening, the examination was re- newed with great diligence, but to no purpose. The
VISITORS. 8l
last faint streak of day gilded the west; beautiful and delicate fleeces of cloud curtained the bed of the sun; the upper sky was studded with stars, and all hopes of seeing the comet that evening had vanished. Soon after we had retired, the officer of the watch announced its appearance in the west. The phenomenon was sublime and beautiful. The needle was greatly agitated, and a strongly marked pencil of light was streaming up from the path of the sun in an oblique direction to the southward and eastward; its edges were parallel. It was 300 long. Stars could be seen twinkling through it, and no doubt was at first entertained that this was the tail of the comet.,,
The tail, as seen in northerly countries, spread over an arc of the heavens of about 400; but in southern latitudes it extended to from 6o° to 700. It had an ab- solute length of two hundred millions of miles; so that, had it been coiled around the earth like a serpent, it would have girdled it eight thousand times at the equator. This comet approached still nearer the sun than that of Newton, and must therefore have been exposed to a heat of greater intensity. Its center is computed to have been within a hundred thousand miles of the solar surface ; and according to Sir John Herschel's calculations, it was then exposed to a heat equal to that which would be received by an equal portion of the earth's service, if it were subject to the influence of forty-seven thousand suns, placed at the common distance of the actual sun. It is difficult to conceive how a flimsy substance in such circumstances could escape being entirely dissipated. But such was 6
82 STORY OF THE SUN, MOON, AND STARS.
its velocity that it wheeled round the sun in less than two hours.
The general question of the probability and the consequences of a collision with a comet may be legit- imately entertained. With reference to the first point, it can not be denied that collision is possible ; but, at the same time, it is so extremely improbable that it may be safely dismissed from apprehension. The fact of such an event not having been experienced in the known course of terrestrial history is surely some guarantee against its occurrence. Another may be found in the small volume of the earth and of comets when compared with the immensity of space in which they move. According to the well-understood prin- ciples of probabilities, Arago has calculated that, upon the appearance of a new comet, the odds are as 281,- 000,000 to 1, that it will not strike against our globe. But even supposing collision to occur, all that we know of the constitution of comets justifies the con- clusion that the encounter would involve no terrestrial convulsion, nor any result incompatible with full se- curity to life and happiness.
So much for the largest members of our circle — largest, though lightest; members some, visitors oth- ers. Now we turn to the smallest.
CHAPTER VIII.
LITTLE SERVANTS.
If you walk out any night after dark, and watch the bright stars shining in a clear sky — shining as they have done for ages past — you will probably see, now and then, a bright point of light suddenly appear, dart along a little distance, and as suddenly vanish. That which you have seen was not the beginning of a story, but in ninety-nine cases out of a hundred it was the end of a story. The little shooting-star was in existence tlong before you saw him, whirling through space with millions of little companions. But he has left them all, and dropped to earth. He is a shooting-star no longer.
If such a journey to the moon as the one described two chapters back were indeed possible, the voyage aloft would hardly be so easily and safely performed as is there taken for granted. Putting aside the thought of other difficulties, such as lack of convey- ance and lack of air, there would be the danger of passing through a very considerable storm of mis- siles— a kind of " celestial cannonade" — which, to say the least, would prove very far from agreeable.
These " starlets" and " meteor planets," as they have been called, are not visible in a normal condition, because of their minuteness. But on entering our at- mosphere they are rendered luminous, owing to the heat evolved by the sudden and violent compression
83
84 STORY OF THE SUN, MOON, AND STARS.
of the air in front of the moving body. According to this view, shooting-stars, which simply dart across the heavens, may be regarded as coming within the limits of the atmosphere, and carried out of it again, by their immense velocity, passing on in space. Meteoric
METEOR EMERGING FROM BEHIND A CI^OUD (NOV. 23, 1877).
showers may result from an encounter with a group of these bodies, while aerolites are those which come so far within the sphere of the earth's attraction as to fall to its surface. More than two thousand years ago the Greeks venerated a famous stone which fell from the heavens on the river iBgos.
It will scarcely be believed what numbers of these shooting-stars or meteorites constantly fall to the earth. As she travels on her orbit, hurrying along at the rate of nineteen miles each second, she meets them by
LITTLE SERVANTS. 85
tens of thousands. They too, like the earth, are jour- neying round the great center of our family. But they are so tiny, and the earth by comparison is so immense, that her strong attraction overpowers one after another, drags it from its pathway, and draws it to herself.
And then it falls, flashing like a bright star across the sky, and the little meteorite has come to his end. His myriads of companions, hastening still along their heavenly track — for the meteorites seem to travel com- monly in vast flocks or companies — might, had they sense, mourn in vain for the lost members of their family.
Any one taking the trouble to watch carefully some portion of the sky after dark, may expect to see each hour about four to eight of these shooting-stars — ex- cept in the months of August and November, when the number is much larger. About six in an hour does not sound a great deal. But that merely means that there have been six in one direction, and near enough for you to see. Somebody else, watching, may have seen six in another direction; and some- body else, a few miles away, may have seen six more. It is calculated that, in the course of every twenty- four hours, about four hundred millions of meteorites fall to earth, including those visible only through telescopes.
This is rather startling. What if you or I should some day be struck by one of these solid, hard little bodies, darting as they do towards earth with speed swifter than that of a cannon-ball? True, they are not really stars, neither are they really planets. But
86 STORY OF THE SUN, MOON, AND STARS.
they are, to say the least, often much larger than a cannon-ball, and a cannon-ball can destroy life.
Four hundred millions every twenty-four hours! Does it not seem singular that we do not see them constantly dropping to the ground? The truth is, we should see them, and feel them too, and dire would be the danger to human life, but for a certain pro- tecting something folded round this earth of ours to ward off the peril. That "something" is the earth's atmosphere. But for the thick, soft, strong, elastic air through which the meteorites have to pass, they would fall with fearful violence, often doing terrible mischief. As it is, we are guarded. The shooting- star, drawn by the earth's attraction, drops into her atmosphere, darting with tremendous speed. In con- sequence of this speed and the resistance of the air, it catches fire. That is when we first see it. The meteorites are believed to appear at a height of about seventy miles, and to disappear at a height of about fifty miles. So that, in one instant's flash, the shoot- ing-star has traveled some twenty miles toward us. Then the light goes out. The little meteorite is burnt. It falls to earth still; but only as fine dust, sinking harmlessly downward.
The meteorites do not always vanish so quickly. Now and then a larger one — too large to be rapidly burnt — does actually reach the ground. If any man were struck by such a stone he would undoubtedly be killed.
When meteorites thus fall to earth they are usually called aerolites. Some are found no bigger than a man's fist, while others much exceed this size. There
LITTLE SERVANTS. 87
is one, kept carefully in the British Museum, which weighs three tons and a half; and we hear of another, lying in South America, between seven and eight feet in length. Such a sky-visitant would be very unwel- come in any of our towns.
We must remember that, whatever size an aerolite may be when it reaches the earth, it must have been far greater when journeying round the sun, since a good part of it has been burnt away during its rush downward through the earth's atmosphere.
Meteors, or bolides, or fireballs, are of much the same nature as meteorites; but they are larger, longer to be seen, and slower in movement. Also, it is not uncommon for them to burst with a loud explosion. Early in the present century such a meteor visited Normandy. It exploded with a noise like the roll of musketry, scattering thousands of hot stones over a distance of several miles. A great number of them were collected, still smoking. The largest of these stones weighed no less than twenty pounds. Hap- pily no one seems to have been injured. Other such falls have taken place from time to time. Sometimes bright, slowly-moving meteors have been seen, looking as large as the moon.
A remarkable fireball appeared in England on November 6, 1869. This fireball was extensively seen from different parts of the island, and by com- bining and comparing these observations, we obtain accurate information as to the height of the object and the velocity with which it traveled. It appears that this meteor commenced to be visible at a point ninety miles above Frome, in Somersetshire, and that
88 STORY OF THE SUN, MOON, AND STARS.
it disappeared at a point twenty-seven miles over the sea, near St. Ives, in Cornwall. The whole length of its course was about 170 miles, which was performed in a period of five seconds, thus giving an average ve- locity of thirty-four miles a second. A remarkable feature in the appearance which this fireball pre- sented was the long, persistent streak of luminous cloud, about fifty miles long and four miles wide, which remained in sight for fully fifty minutes. We have in this example an illustration of the chief fea- tures of the phenomena of a shooting-star presented on a very grand scale. It is, however, to be observed that the persistent luminous streak is not a universal, nor, indeed, a very common characteristic of a shoot- ing-star.
If we may liken comets to the fishes of the Solar System — and in their number, their speed, their vary- ing sizes, their diverse motions, they may be fairly so likened — we may perhaps speak of the meteorites as the animalcula of the Solar System. For, in com- parison with the planets, they are, in the matter of size, as the animalcula of our ponds in comparison with human beings. In point of numbers they are countless.
Take a single drop of water from some long-stag- nant pond, and place it under a powerful microscope. You will find it to be full of life, teeming with tiny ani- mals, darting briskly to and fro. The drop of water is in itself a world of living creatures, though the naked eye of man could never discover their existence. So with the meteorites. There is good reason to be- lieve that the Solar System fairly teems with them.
LITTLE SERVANTS. 89
We talk of "wide gaps of empty space," between the planets; bnt how do we know that there is any snch thing as empty space to be found throughout all the sun's domain?
Not only are the meteorites themselves countless, a matter easily realized, but the families or systems of meteorites appear to be countless also. They, like the systems of Jupiter and Saturn, are each a family within a family — a part of the Solar System, and yet a complete system by themselves. Each circles round the sun, and each consists of millions of tiny meteor- ites. When I say "tiny," I mean it of course only by comparison with other -heavenly bodies. Many among them may possibly be hundreds of feet and even more in diameter, but the greater proportion appear to be much smaller. It is not impossible that multitudes beyond imagination exist, so small in size that it is impossible we should ever see them, since their dying flash in the upper regions of our atmosphere would be too faint to reach our sight.
The earth, traveling on her narrow orbit round the sun, crosses the track of about one hundred of these systems, or rings. Sometimes she merely touches the edge of a ring, and sometimes she goes into the very thick of a dense shower of meteorites. Twice every year, for instance, on the 10th of August and the nth of November, the earth passes through such a ring, and very many falling stars may be seen on those nights. Numbers of little meteorites, dragged from their orbits and entangled in the earth's atmosphere, like a fly caught in a spider's web, give their dying flash, and vanish. It used to be supposed that the
9o
STORY OF THE SUN, MOON, AND STARS.
August and November meteorites belonged to one single system ; but now they are believed to be two entirely distinct systems.
The comet discovered on February 27, 1827, by Biela, and ten days later at Marseilles by Gambart, who recognized that it was the same as that of 1772
THE GREAT SHOWER OF SHOOTING-STARS, NOVEMBER 27, 1872.
and 1805, returned six and a half years later, in 1832. In fact it crossed, as we have seen, the plane of the terrestrial orbit at the respectable distance of fifty millions of miles from the earth; but if there was any danger in this meeting, it was rather for it than for us; for it was certainly strongly disturbed in its course. It returned in 1839, but under conditions too unfavorable to enable it to be observed — in the month of July, in the long days, and too near the sun. It was seen again in 1845, on November
LITTLK SERVANTS. 91
25th, near the place assigned to it by calculation, and its course was duly followed. Everything went on to the general satisfaction, when — unexpected spectacle! — on January 13, 1846, the comet split into two! What had passed in its bosom? Why this separation? What was the cause of such a celestial cataclysm? We do not know; but the fact is, that instead of one comet, two were henceforth seen, which continued to move in space like two twin-sisters — two veritable comets, each having its nucleus, its head, its coma, and its tail, slowly separating from each other. On February 10th there was already a hundred and fifty thousand miles of space between the two. They would seem, however, to have parted with regret, and during sev- eral days a sort of bridge was seen thrown from one to the other. The cometary couple, departing from the earth, soon disappeared in the infinite night.
They returned within view of the earth in the month of September, 1852. On the 26th of this month the twins reappeared, but much farther apart, separated by an interval of twelve hundred and fifty thousand miles.
But this is not the strangest peculiarity which this curious body presented to the attention of astronomers. The catastrophe which was observed in 1846 was only a presage of the fate which awaited it; for now its ex- istence is merely imagined, the truth being that this comet is lost. Since 1852 all attempts to find it again have been unavailing.
To be lost is interesting, especially for a comet. But this, doubtless, was not enough; for it reserved for us a still more complete surprise. Its orbit inter-
92 STORY OF THE SUN, MOON, AND STARS.
sects the terrestrial orbit at a point which the earth passes on November 27th. Well, nothing more was thought about it — it was given up as hopeless, when, on the evening of November 27, 1872, there fell from the sky a veritable rain of shooting stars. The ex- pression is not exaggerated. They fell in great flakes. Lines of fire glided almost vertically in swarms and showers — here, with dazzling globes of light; there, with silent explosions, recalling to mind those of rock- ets; and this rain lasted from seven o'clock in the evening till one o'clock next morning, the maximum being attained about nine o'clock. At the observatory of the Roman College, 13,892 were counted; at Mont- calieri, 33,400; in England a single observer counted 10,579, etc. The total number seen was estimated at a hundred and sixty thousand. They all came from the same point of the sky, situated near the beautiful star Gamma of Andromeda.
On that evening I happened to be at Rome, in the quarter of the Villa Medicis, and was favored with a balcony looking towards the south. This wonderful rain of stars fell almost before my eyes, so to say, and I shall never cease regretting not having seen it. Convalescent from a fever caught in the Pontine Marshes, I was obliged to go into the house immedi- ately after the setting of the sun, which on that even- ing appeared from the top of the Coliseum to sleep in a bed of purple and gold: My readers will understand what disappointment I felt next morning when, on go- ing to the observatory, Father Secchi informed me of that event! How had he observed it himself? By the most fortunate chance : A friend of his, seeing the
LITTLE SERVANTS. 93
stars fall, went to him to ask an explanation of such a phenomenon. It was then half-past seven. The spec- tacle had commenced; but it was far from being fin- ished, and the illustrious astronomer was enabled to view the marvelous shower of nearly fourteen thousand meteors.
This event made a considerable stir in Rome, and the pope himself did not remain indifferent ; for, some days afterwards, having had the honor of being re- ceived at the Vatican, the first words that Pius IX ad- dressed to me were these: " Have you seen the shower of Danae?" I had admired, some days before in Rome, some admirable "Danaes," painted by the great masters of the Italian school in a manner which left nothing to be desired; but I had not had the privilege of finding myself under the cupola of the sky during this new celestial shower, more beautiful even than that of Jupiter.
What was this shower of stars? Evidently — and this is not doubtful — the encounter with the earth of myriads of small particles of matter moving in space along the orbit of Biela's comet. The comet itself, if it still existed, would have passed twelve weeks be- fore. It was not, then, to speak correctly, the comet itself which we encountered, but perhaps a fraction of its decomposed parts, which, since the breaking-up of the comet in 1846, would be dispersed along its orbit behind the head of the comet.*
* No doubt can remain of the identity of this swarm of shoot- ing-stars with the cotfiet of Biela. On November 27, 1885, the same encounter occurred. A magnificent shower of stars was ob- served all over Europe just at the moment when the earth crossed the comet's orbit.
94 STORY OF THE SUN, MOON, AND STARS.
Once in every thirty-three years we have a grand display of meteorites in November ; tens of thousands being visible in one single night. The meteorites in that ring have their "year" of thirty-three earthly years, and once in the course of that long year our earth's orbit carries her deep into their midst. In this single November ring there are myriads upon myriads of meteorites, spreading through millions of miles of space.
Yet this system is but one among many. There is no reason whatever to suppose that the streams of me- teorites cluster more thickly about the orbit of the earth, than in other parts of the Solar System. No doubt the rest of the planets come across quite as many. Indeed, the wonderful rings of Saturn are probably formed entirely of meteorites — millions upon millions of them whirling round the planet in a reg- ular orbit-belt, lit up by the rays of the sun. Also it is believed that the meteorite families cluster more and more closely in the near neighborhood of the sun, rushing wildly round him, and falling by millions into the ocean of flame upon his surface. It has even been guessed that they may serve in part as fuel to keep up his mighty furnace heat.
There is a curious cone-shaped light seen some- times in the west after sunset. It is called the "Zo- diacal L,ight," and men have often been much puzzled to account for it. The shining is soft and dim, only to be seen when the sky is clear, and only to be seen in the neighborhood of the sun. This, too, may be caused by reflected light from countless myriads of meteorites gathering thickly round the sun.
CHAPTER IX.
NEIGHBORING FAMILIES.
WE have now to take flight in thought far, far be- yond the outskirts of our little Solar System. Yes, our great Solar System, with its mighty sun, its planets, its moons, its comets and meteorites, its ceaseless motions, its vast distances, — even all this sinks to littleness beside the wider reaches of space which now have to be pictured to our minds. For our sun, in all his greatness, is only a single star — - only one star among other stars — and not by any means one of the largest of the stars.
How many stars are there in the sky? I^ook over- head some cloudless night, and try to count the brill- iant points of light. " Millions," you would most likely give as your idea of their number. Yet you would be wrong; for you do not really perceive so many. The stars visible to man's naked eye have been mapped and numbered. It is found that from two to three thousand are, as a rule, the utmost ever seen at once, even on a favorable night, and with par- ticularly good sight.
But what is actually the full number of the stars? Two or three thousand overhead. Five or six thou- sand round the whole world. So much visible to man's unaided eyes. Ah, but take a telescope, and see through it the opening fields of stars beyond stars. Take a stronger telescope, and note how, as you pierce
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96 STORY OF THE SUN, MOON, AND STARS.
deeper into space, fresh stars beyond fresh stars shine faintly in the measnreless distance. Take the most powerful telescope ever made, and again it will be the same story.
There has been a chart or map drawn of known stars in the northern hemisphere — including those visible in telescopes down to a certain magnitude — containing over three hundred thousand. But that is only a part of even what man can see. Sir William Herschel calculated roughly that the number of stars within reach of his powerful telescope, round the whole earth, amounted probably to something like twenty millions.
Twenty millions of suns ! For that is what it really means. Twenty millions of radiant, burning, heav- enly bodies — some the same size as our sun; some larger, perhaps very much larger ; some smaller, per- haps very much smaller; but all suns. And any number of these suns may have, just like our own, families of planets traveling round them, enjoying their light and their heat.
We talk about stars of the first, second, and other magnitudes. Stars can be seen without a telescope as low down as the sixth magnitude ; after that they become invisible to the naked eye. This word " mag- nitude " is rather misleading. "Magnitude" means size, and whatever the real size of the stars may be, they have to our sight no seeming size at all. So when we speak of different magnitudes, we really mean different brightnesses. The brightest stars are those of the first magnitude, the next brightest those of the second magnitude, and so on. No doubt many
NEIGHBORING FAMILIES. 97
a star of the third or fourth magnitude is really much larger than many a star of the first or second magni- tude, only being farther away it shines more dimly, or the higher-magnitude star may in itself possess greater natural brilliancy.
Of first-magnitude stars there are altogether about twenty; of second-magnitude stars about sixty-five; of third-magnitude stars about two hundred; and so the numbers increase till of the sixth-magnitude stars we find more than three thousand. These are all that can be commonly seen with the naked eye, amounting to five or six thousand. With telescopes the numbers rise rapidly to tens of thousands, hundreds of thou- sands, and even millions.
For a long while it was found quite impossible to measure the distances of the stars. To this day the distances of not over two dozen, among all those tens of thousands, have been discovered. The difficulty of finding out the distance of the sun was as nothing compared with the difficulty of finding out the dis- tances of the stars.
No base-line sufficient for the purpose could for years be obtained. I must explain slightly what is meant by a " base-line. " Suppose you were on the brink of a wide river, which you had no means of crossing, though you wished to discover its breadth. Suppose there were on the opposite brink a small tree, standing alone. As you stood, you would see the tree seeming to lie against a certain part of the country beyond. Then, if you moved along your bank some fifty paces, the tree would seem to lie against quite a different part of the country beyond. 7
98 STORY OF THE SUN, MOON, AND STARS.
Now if you had a long piece of string to lay down along the fifty paces yon walked, and if two more pieces of string were tied, one from each end of the fifty paces, both meeting at the tree, then the three pieces of string would make one large triangle, and the " fifty paces" would be the "base" of your tri- angle.
If you could not cross the river, you could not of course tie strings to the tree. But having found your base-line, and measured its exact length, and having also found the shape of the two angles at its two ends, by noting the seeming change of the tree's position, it would then be quite easy to find out the distance of the tree. The exact manner in which this calcula- tion is made can hardly be understood without some slight knowledge of a science called trigonometry. The tree's distance being found, the breadth of the river would be known.
This mode of measuring distance was found com- paratively easy in the case of the moon. But in the case of the sun there was more difficulty, on account of the sun's greater distance. No base-line of ordinary length would make the sun seem to change his posi- tion in the sky in the slightest degree. Nor till the very longest base-line on the earth was tried could the difficulty be overcome. That base-line is no less than eight thousand miles long. One man standing in England looking at the sun, and another man stand- ing in Australia looking at the sun, have such a base- line lying between them, straight through the center of the earth.
In the case of the stars this plan was found useless.
NEIGHBORING FAMILIES. 99
So closely has the sky been mapped out, and so ex- actly is the place of each star known, that the tiniest change would have been at once noticed. Not a star showed the smallest movement. The eight thousand miles of the earth's diameter was a mere point with regard to them.
A bright idea came up. Here was our earth trav- eling round the sun, in an orbit so wide that in the middle of summer she is over one hundred and eighty millions of miles away from where she is in the mid- dle of winter. Would not that make a magnificent base-line? Why not observe a star in summer and observe the same star again in winter, and then calcu- late its distance.
This, too, was done. For a long while in vain! The stars showed no signs of change, beyond those due to causes already known. Astronomers persevered, however, and with close and earnest care and improved instruments, success at last rewarded their efforts. A few — only a few, but still a few — of those distant suns have submitted to the little measuring-line of earth, and their distance has been roughly calculated.
Now, what is their distance? Alpha Centauri, the second star which was attempted with success, is the nearest of all whose distance we know. You have heard how far the sun is from the earth. The dis- tance of Alpha Centauri is two hundred and seventy-five thousand times as much. Can you picture to yourself that vast reach of space — a line ninety-three millions of miles long, repeated over and over again two hun- dred and seventy-five thousand times ?
But Alpha Centauri is one of the very nearest.
IOO STORY OF THE SUN, MOON, AND STARS.
The brilliant Sirius is at least twice as far away. Others utterly refuse to show the smallest change of position. It is with them, as had been said, much the same as if a man were to look at a church- steeple, twenty miles distant, out of one pane in a window, and then were to look at it out of the next pane. With the utmost attention he would find no change of position in the steeple. And like the base- line of two glass panes to that steeple, so is the base- line formed by our whole yearly journey to thousands of distant stars. We might measure how far away they are, only the longest base-line within our reach is too short for our purpose.
The planet Neptune has a wider orbit than ours. But even his orbit, seen from the greater number of the stars, would shrink to a single point. After all, how useless to talk of two hundred and seventy-five thousand times ninety-three millions of miles ! What does it mean? We can not grasp the thought.
Let us look at the matter from another view. Do you know how fast light travels — this bright light shining round us all day long? Light, so far as we know, does not exist everywhere. It travels to and fro, from the sun to his planets, from the planets to one another ; from the sun to the moon, from the moon to the earth, and from the earth to the moon again.
Light takes time to travel. This sounds singular, but it is true. Light can not pass from place to place in no time. Light, journeying through space, is invis- ible. Only when it strikes upon something, whether a solid body or water or air, does it become visible to
NEIGHBORING FAMILIES. IOI
our eyes. The shining all round us in the day-time is caused by the sunlight being reflected, not only from the ground, but from each separate particle of air. If we had no atmosphere, we should see still the bright rays falling on the ground, but the sky above would be black. Yet that black sky would be full of mil- lions of light-rays, journeying hither and thither from sun and stars, invisible except where they alight upon something.
The speed of light is far beyond that of an express train, far beyond that of the swiftest planet. In one tick of the clock, Mercury has rushed onward twenty- nine miles. In one tick of the clock, storm-flames upon the surface of the sun will sweep over two or three hundred miles. But in one tick of the clock a ray of light flashes through one hundred and eighty- six thousand three hundred and thirty-seven miles.
One hundred and eighty-six thousand miles ! That is the same as to say that, during one single instant, a ray of light can journey a distance equal to about eight times round and round our whole earth at the Equator.
By using this wonderful light-speed as a measure- ment, we gain clearer ideas about the distances of the stars. A ray of light takes more than eight minutes to pass from the sun to the earth. L,ook at your watch, and note the exact time. See the hand moving slowly through the minutes, and imagine one single ray of light, which has left the sun when first you looked, flashing onward and onward through space, one hun- dred and eighty-six thousand miles each second. Eight minutes and a half are over. The ray falls upon your
102 STORY OF THE SUN, MOON, AND STARS.
hand. In those few minntes it has journeyed ninety- three millions of miles.
So much for the sun's distance. How about the stars? Alpha Centauri, a bright star seen in the southern hemisphere, is one of our nearest neighbors. Yet each light-gleam which reaches the eye of man from that star, left Alpha Centauri four years and a third before. During four years and a third, from the moment when first it quitted the surface of the blazing sun, it has flashed ceaselessly onward, one hundred and eighty-six thousand miles each second, dwindling down with its bright companion-rays from a glare of brilliancy to a slender glimmer of light till it reaches the eye of man. Four years and a third sounds much, side by side with the eight minutes' journey from the sun. Sound would take more than three millions of years to cross the same abyss. At the constant ve- locity of thirty-seven miles an hour, an express-train starting from the sun Alpha Centauri would not reach the earth until after an uninterrupted course of nearly seventy-five millions of years.
This is our neighbor star. The second, the near- est after it, is nearly double as far, and is found in quite another region of space, in the constellation of Cygnus, the Swan, always visible in our northern hemisphere. If we wish to understand the relative situation of our sun and the nearest two, let us take a celestial globe, and draw a plane through the center of the globe and through Alpha Centauri and 61 Cygni. We shall thus have before us the relation which exists between our position in infinitude and those of these two suns. The angular distance which
NEIGHBORING FAMILIES. IO3
separates them on the celestial sphere is 1250. Let us make this drawing, and we shall discover certain rather curious particulars. In the first place, these two nearest stars are in the plane of the Milky Way, so that we can also represent the Milky Way on our drawing; again, this celestial river is divided into two branches, precisely in the positions occupied by these two nearest stars, the division remaining marked along the whole interval which separates them. This drawing shows us, further, that if we wish to trace the curve of the Milky Way with reference to the distance of our two stars, it will be nearer to us in the con- stellation of the Centaur than in that of the Swan ; and, in fact, it is probable that the stars of that region of the sky are nearer than those of the opposite re- gion. Another very curious fact is, that both the nearest stars are double.
But look at Sirius, that beautiful star so familiar to us all. The light which reaches you to-night, left his surface from nine to ten years ago. Look at the Little Bear, with the Pole-star shining at the end of his tail. That ray of soft light quitted the Pole-star some forty years ago. Almost half a century it has been speed- ing onward and ever onward, with ceaseless rapidity, till its vast journey is so far accomplished that it has reached the earth. Look at Capella, another fair star of the first magnitnde. The light which reaches you from her has taken over thirty years to perform its voyage. Ten, thirty, forty years — at the rate of 186,000 miles per second!
These stars are among the few whose distance can be roughly measured. Others lie at incalculable dis-
104 STORY OF THE SUN, MOON, AND STARS.
tances beyond. There are stars whose light must, it is believed, have started hundreds or even thousands of years before the soft, faint ray at length reaches the astronomer's upturned eye through the telescope.
Look at Capella, how gently and steadily she shines! You see Capella, not as she is now, but as she was thirty years ago. Capella may have ceased to exist meantime. The fires of that mighty sun may have gone out. If so, we shall by and by learn the fact — more than thirty years after it happened. Look at the Pole-star. Is there any Pole-star now? I can not tell you. I only know there was one, forty years ago, when that ray of light started on its long journey. Stars have ceased to shine before now. What may have happened in those forty years, who can say? Look at that dim star, shining through a powerful telescope with faint and glimmering light. We are told that in all probability the tiny ray left its home long before the time of Adam.
There is a strange solemnity in the thought. Hun- dreds of years ago — thousands of years ago — -some say, even tens or hundreds of thousands of years ago ! It carries us out of the little present into the unknown ages of a past eternity.
If the neighboring stars are placed at tens and hundreds of trillions of miles from us, it is at quad- rillions, at quintillions of miles that most of the stars lie which are visible in the sky in telescopic fields. What suns! what splendors! Their light comes from such distances ! And it is these distant suns which human pride would like to make revolve round our atom ; and it was for our eyes that ancient theology
< NEIGHBORING FAMILIES. 105
declared these lights, invisible without a telescope, were created ! No contemplation expands the thought, elevates the mind, and spreads the wings of the soul like that of the sidereal immensities illuminated by the suns of infinitude. We are already learning that there is in the stellar world a diversity no less great than that which we noticed in the planetary world. As in our own Solar System the globes already studied range from 6 miles in diameter (satellites of Mars) up to 88,ooo miles (Jupiter) — that is to say, in the proportion of I to 14,000 — so in the sidereal system the suns present the most enormous differences of volume and brightness: 61 Cygni, the stars numbered 2,398 in the catalogue of Lalande, and 9,352 in the catalogue of L,acaille, and others of the eighth or ninth magnitude, are incomparably smaller or less luminous than Sirius, Arcturus, Capella, Canopus, Rigel, and the other brilliants of the firmament.
CHAPTER X.
OUR NEIGHBORS' MOVEMENTS.
How high ! how distant ! how mighty ! How little we know about them, yet how overwhelming the little we know, and how wonderful that we do know it!
We have now to consider the movements of these distant neighbors — first, their seeming movements; secondly, their real movements.
I have already spoken about the seeming motions of the stars as a whole, once believed to be real, and now known to be only caused by the motions of our earth. For just as the turning of the earth upon her axis makes the sun seem to rise every morning in the east, and to set every evening in the west, so that same continued turning makes the stars seem to rise every evening in the east and to set every morning in the west.
When we speak of the stars as rising in the east, we do not mean that they all rise at one point in the east, but that all rise, more or less, in an easterly di- rection— northeast, east, and southeast. So also with respect to the west. It is to the east and west of the earth as a whole that they rise and set — not merely to the east and west of that particular spot on earth where one man may be standing. All night long fresh stars are rising, and others are setting, and if it were not for the veil of light made by the sunshine in our atmosphere, we should see the same going on all day long as well.
106
our neighbors' movements. 107
There are some constellations, or groups of stars, always visible at night in our northern hemisphere ; and there are some constellations never visible to us, but only seen by people living in the southern hemi- sphere— in Australia, for instance. There are other constellations which appear in summer and disappear in winter, or which appear in winter and disappear in summer. This change is caused by our earth's jour- ney round the sun. It is not that the constellations have altered their place in the heavens with respect to the other constellations, it is merely that the earth has so altered its position in the heavens that the groups of stars which a short time ago were above the horizon with the sun by day are now above the hori- zon without him by night.
Mention has been a good many times made of the axis of the earth ending in the North and South Poles. If this axis were carried straight onward through space, a long, slender pole passing upwards into the sky without any bend, from the North Pole in one direction and from the South Pole in the other, — this would be the pole of the heavens. The places of the stars in the sky are counted as "so many degrees" from the North and South Celestial Poles, just as the places of towns on earth are counted as "so many degrees" from the North and South Poles of earth. There are atlases of the sky made as well as atlases of the earth.
The constellation of the Great Bear is known to all who have ever used their eyes at all to watch the heavens. Almost equally well known are the two bright stars in this constellation named the Pointers,
108 STORY OF THE SUN, MOON, AND STARS.
because, taken together, they point in nearly a straight line to a certain important star in the end of the Little Bear's tail, not very distant.
This star, important less from its brightness than from its position, lies close to that very spot in the heavens where the celestial North Pole passes. It is called the Pole-star. Night after night, through the year, it there remains, all but motionless, never going below the horizon for us in the northern hemisphere, or northern half of the earth ; never rising above the
CONSTEIXATION OF THE GREAT BEAR.
horizon for those in the southern hemisphere. It shines ever softly and steadily in its fixed position. If you travel further south, the Pole-star sinks down- ward towards the horizon. If you travel further north, the Pole-star rises higher above the horizon. If you were at the North Pole, you would see the Pole- star exactly overhead.
Very near the Pole-star is the constellation of the Great Bear, with Cassiopeia nearly opposite on the other side of the Little Bear, and other groups be- tween the two, completing the circle. These con- stellations do not, to us who live in the northern hemisphere, rise or set; for they simply move in a
OUR neighbors' movements.
109
circle round and round the Pole-star, never going be- low the horizon. All day and all night long this circling movement continues, though only visible at
THE GREAT BEAR 50,000 YEARS AGO.
night. It is caused entirely by the earth's own motion on her axis.
Lower down, or rather further off from the Pole- star, comes another ring of constellations. These in
THE GREAT BEAR 50,000 YEARS HENCE.
just the same manner appear to travel round and round the Pole-star. But being further away, each dips in turn below the horizon — or, as we call it, each sets and rises again. And by the time we come to yet another circle of leading constellations, we reach
IIO STORY OF THE SUN, MOON, AND STARS.
those which are so far affected by the earth's yearly journey as to be only visible through certain months, and to be hidden during other months.
If we could stand exactly at the North Pole, during part of its six months' night, we should see the Pole- star just overhead, and all the constellations circling round it once in every twenty-four hours. Those
CONSTKIXATION OF ORION, AS IT APPEARS NOW.
nearest would move slowly, in a small ring. Those furthest, and lowest down, would in the same length of time sweep round the whole horizon. But the stars would not there seem to rise or set. If we were standing at the South Pole, we should see exactly the same kind of seeming movement, only with altogether a different set of stars. If we were standing on the Equator at night, we should see the rising and set- ting very plainly. The whole mass of stars would appear to rise regularly and evenly in an easterly di- rection, to pass steadily across the sky, each taking
OUR neighbors' movements.
Ill
its own straightforward path, and to set in a westerly direction.
We who are placed midway between the Pole and the Equator, see a mixture of these two motions. Some stars seem to circle round and round, as all would do if we stood at the North Pole. Some stars seem to rise and set, as all would do if we stood at the Equator. So much for the seeming movements of the stars.
But now, about their real movements. Are the stars fixed, or are they not? These seeming daily and yearly motions do not af- fect the question, being merely caused by our own motions. Trees and hedg- es may appear to move as we rush past them in a train, yet they are really fixed.
During a long while, conspiration of orion 50,000
. . . . ° , YEARS FROM NOW.
after it was found out that
the quick, daily movements of all the stars in com- pany were merely apparent, men believed that they really had no ''proper motions" — that is, no move- ments of their own. For century after century the constellations remain the same. Hundreds of years ago the seven chief stars of the Great Bear shone in company as they shine now. Who could suppose that each one of those seven stars is hurrying on its path through space with a speed exceeding far that of the
BETELGEUSE..-0
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ALDEBARANq
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112 STORY OF THE SUN, MOON, AND STARS.
swiftest express-train? Yet so it is. Hundreds of years ago trie grand group of Orion, with belt and sword, gleamed brilliantly night by night as it gleams in these days ; and Cassiopeia had her W form, and Hercules and Draco and Andromeda were shaped as they are shaped still. Who would imagine that through those hundreds of years each star of these different constellations was hastening with more or less of speed along its heavenly road ? Yet so it is.
Cases have been decisively ascertained of stars changing their places among the other stars by a slow and gradual motion. Three of the most conspicuous of them — Sirius, Arcturus, and Aldebaran — have been proved, by the comparison of modern with some an- cient observations, to have experienced a change of place to the southward, to the extent of more than the breadth of the moon in all the three. And during the period of accurate modern measurement, other instances have been ascertained of steady change of place by the effect of proper motion.
But if the stars are thus rapidly moving in all di- rections, how is it that we do not see them move ? How is it that, night after night, year after year, century after century, even thousand years after thousand years, the shapes of the constellations remain un- altered?
Suppose you and I were standing on the sea- shore together, watching the movements of scores of sea-craft, little boats and large boats, steamers, yachts, and ships. Suppose we stood through a full quarter of an hour looking on. Some might move, it is true, very slowly ; yet their movements in every case would
our neighbors' movements. 113
plainly be seen. There could be no possibility of mistaking the fact, or of supposing them to be "fixed." Just so we see the nearer planets move. Ivittle danger of our supposing them to be "fixed stars."
In the matter of the stars themselves, we must carry our illustration further. Come with me up to the top of that lofty hill on the border of the sea, and let us look from the cliff. We see still the move- ments among boats and smacks, yachts and steamers, only the increased distance makes the movements seem slower. But our view is widened. Look on the far horizon and see three distant dots, which we know to be ships — one and two close together, and a third a little way off, making a small constellation of vessels. Watch them steadily for a quarter of an hour. You will detect no movement, no increased distance or nearness between any two of the three. The group remains unchanged.
Are they really moving? Of course they are, more or less rapidly, probably with differing speed and in different directions. But at so great a distance, one quarter of an hour is not long enough for their mo- tions to become visible to the naked eye. If we could watch longer — say, for two or three hours — ah, that would make all the difference ! If only we could watch longer ! But the hundreds, and even thousands of years during which men have watched the stars, sink, at our vast distance, into no more than one quar- ter of an hour spent in watching the far-off ships from the high hilltop. The motions can not be detected. In ten thousand years you might see something. In
114 STORY OF THE SUN, MOON, AND STARS.
fifty thousand years you might see much. But four or five thousand years are not sufficient.
One other mode there is, by means of which the movements of the ships on the horizon might be made plain. Suppose you had no more than the quarter of an hour to spare, but suppose you had at your com- mand a powerful telescope. Then you may practically bring the ships nearer, and by magnifying the small, slow, distant motions, you may make them, as it were, larger, quicker, more easy to see.
Telescopes will do this for us, likewise, in the mat- ter of the stars. By means of telescopes, with the as- sistance of careful watching and of close calculation it has been found that the stars are really moving quickly, each one in his own pathway. The very speed of some of them has been measured.
Arcturus is one of those stars, the motions of which are most plainly to be seen. In the course of about one thousand years he changes visibly his place in the sky by a space equal to the apparent diameter of the moon. The seeming movement of Arcturus in one thousand years is the same as the seeming width of the round moon that we see.
But the actual speed with which Arcturus rushes through space is said to be no less than fifty-four miles each second, or not far from two hundred thou- sand miles an hour. That is nearly three times as fast as our own earth's motion round the sun. How enormous the distance must be which can shrink such speed to such seeming slowness !
Another beautiful star, Capella, is believed to travel at the rate of thirty miles each second. The speed
our neighbors' movements. 115
of Sirius is slower, being only fourteen miles a second. The Pole-star creeps along at the rate of only one mile and a half each second.
So also with the rest of the stars. There seems good reason to believe that every star we see shining in the heavens, every star visible in powerful tele- scopes, is perpetually hastening onward. But hasten- ing whither? God knows ! We do not.
In all probability not one of the tens of millions of stars which may be seen through telescopes is in repose. This is a matter of conjecture, of reasoning from analogy, and of reasoning also from the working of known laws. We know, as a consequence of direct observation, apart from the new spectroscopic method, that at least hundreds are upon the wing. We assume, as a matter of the greatest possible likelihood, that all the millions besides, which can not be actually seen to stir, are equally on the move. Knowing what we do know of the laws by which the universe of stars is governed, it seems to us an absolute impossibility that any single star, amid the whole vast host, can be or could be permanently at rest.
If by any means a star were brought to repose — what then would happen? It would inevitably start off again, drawn by the attraction of other stars. From whatever direction the strongest pull came, the impulse would be given. Lengthened repose would be out of the question. And this, it seems to us, must be true, not of one star only, here or there, but of every star in the enormous host of radiant suns which make up the mighty Stellar System.
Our forefathers, one thousand years ago, could not
n6 story of the; sun, moon, and stars.
measure the precise positions of individual stars, as astronomers now are able to do. They had no modern observatories, no telescopes, no spectroscopes, no pho- tographic appliances. These methods of observation we shall explain in another chapter. Their measure- ments at best were rough, their scientific knowledge was crude. Had we any such accurate observations handed down from one thousand years ago as are made in these days, we should no doubt see clearly many slight differences in the positions of many stars which are not now apparent. But even then we should see no changes sufficient in amount to affect the general outlines of the leading constellations.
A star, which in the course of a century makes visible advance over a space in the sky equal to only a small portion of the breadth of the full moon, is looked upon as a fast voyager. One hundred times this degree of movement, if it took place in a con- siderable number of stars in our sky, would not in centuries very materially change the face of our mid- night heavens.
And all motions which would in the remotest de- gree affect the shapes of constellations, must be side- way motions. Those line-of-sight motions, of which the spectroscope alone tells us, could never have been discovered by simple observation of the sky. Until the new method came to light we had no means whatever of perceiving such movements among the stars.
Suppose you are looking at two men in the dis- tance, upon a wide, flat plain. One of the two is walking very slowly across your line of vision. The
OUR NEIGHBORS* MOVEMENTS. I17
second man is moving very slowly straight towards you. If you watch with care you may find out both the movements. The sideway walking will be ap- parent first and most easily, because, as the man moves, he has constantly a fresh part of the horizon behind him. But in time the advance of the second man towards you will also become apparent; for al- though he is seen still against precisely the same spot on the horizon, he slowly occupies a larger spot on the retina of your eye, — in other words, he seems to grow bigger. And that, as you know from long ex- perience, can only mean increasing nearness.
If a star seemed to grow larger as it drew nearer, we should then be able to perceive that movement also. But no star in the sky ever does seem to grow any larger. Every star is to us but one point of light. It may be rushing towards us at an enormous rate of speed, yet still as a single point it remains, always at the same point in our sky. Therefore we have no chance of perceiving its movement ; or rather, we had no chance until the discovery of this new method. In fact, the very nearest known star is at so enor- mous a distance that, supposing it to be coming to- wards us at the rate of one hundred miles each second, it would still gain, in the course of a century, only one-fortieth part more of brightness than it has now. It would not increase at all in apparent size.
When we leave behind us the thought of starry motions, as we faintly detect them at this great dis- tance, and picture to ourselves the actual far-off whirl of all those glorious suns, the effect upon the mind is overwhelming. Stars are found to be rushing hither
Il8 STORY OF The sun, moon, and stars.
and thither, at every degree of speed, in every imag- inable direction : stars to right, and stars to left ; stars towards us, and stars away from us ; stars alone, and stars in company, — all this, and more, deciphered out of the tiny gleam of quivering light, which streams through the vast abyss of space from each distant orb to earth. So real star-motions were known — first, through telescopic observation; secondly, through spectroscopic observation; and now, lastly, photog- raphy has stepped in, bringing with it much increase of exactitude.
But if all the stars are moving, what of our sun? Our sun is a star. And our sun also is moving. He is pressing onward, in a wide sweep through space, bearing along with him his whole vast family — planets, satellites, comets, meteorites — round or towards some far distant center. For aught we know, every star in the heavens may have a like family traveling with him.
In infinite space the stars are strewn in immense clusters, like archipelagoes of islands in the ocean of the heavens. To go from one star to another in the same archipelago light takes years; to pass from one archipelago to another it takes thousands of years. Each of these stars is a sun similar to ours, sur- rounded, doubtless, at least for the most part, by worlds gravitating in its light; each of these planets possesses, sooner or later, a natural history adapted to its constitution, and serves for many ages as the abode of a multitude of living beings of different species. Attempt to count the number of stars which people the universe, the number of living beings who are born and die in all these worlds, the pleasures and
OUR NEIGHBORS' MOVEMENTS. 1 19
pains, the smiles and tears, the virtues and vices ! Im- agination, stop thy flight!
The sun is not one of the most quickly-moving stars. His rate of speed has not been found out with any certainty, but it is believed to be about four or five miles a second.
And where are we going? This has been in part discovered. If you and I were driving through a forest of trees, we should see the trees on each side of us seeming to move backward, while behind they would close together, and in front they would open out.
Astronomers — and first among them, William Her- schel — reasoned that if our Solar System were really in motion, we ought to be able to see these changes among the stars. And some such changes have be- come visible through careful watching — not so much those ahead and behind as those at the sides.
It is not actually so simple a matter as looking at the trees in a forest, because the trees would be at rest, whereas each star has his own particular real motion, as well as his seeming change of place caused by our sun's motion. It is more like moving in a small steamer at sea, among hundreds of other craft, each of which is going on its own way, at the same time that all on either side seem to move backward because we are moving forward.
So each movement had to be noted, and the real motions had to be separated from the seeming back- ward drift of stars to the right and left of the sun's pathway. The result of all this is that the sun, with his planets, is found to be hastening towards a certain far-off constellation named Hercules.
120 STORY OF THE SUN, MOON, AND STARS.
It is a strange and unexpected fact, but absolutely true, that each sun of space is carried along with a velocity so rapid that a cannon-ball represents rest in comparison ; it is at neither a hundred, nor three hun- dred, nor five hundred yards per second that the earth, the sun, Sirius, Vega, Arcturus, and all the systems of infinitude travel: it is at ten, twenty, thirty, a hundred thousand yards a second ; all run, fly, fall, roll, rush through the void — and still, seen as a whole, all seems in repose.
The immense distance which isolates us from all the stars reduces them to the state of motionless lights apparently fixed on the vault of the firmament. All human eyes, since humanity freed its wings from the animal chrysalis, all minds since minds have been, have contemplated these distant stars lost in the ethe- real depths ; our ancestors of Central Asia, the Chal- deans of Babylon, the Egyptians of the Pyramids, the Argonauts of the Golden Fleece, the Hebrews sung by Job, the Greeks sung by Homer, the Romans sung by Virgil, — all these earthly eyes, for so long dull and closed, have been fixed, from age to age, on these eyes of the sky, always open, animated, and living. Ter- restrial generations, nations and their glories, thrones and altars have vanished : the sky of Homer is always there. Is it astonishing that the heavens were con- templated, loved, venerated, questioned, and admired, even before anything was known of their true beauties and their unfathomable grandeur ?
Better than the spectacle of the sea, calm or agi- tated, grander than the spectacle of mountains adorned with forests or crowned with perpetual snow, the spec-
OUR NEIGHBORS' MOVEMENTS. 121
tacle of the sky attracts us, envelops us, speaks to us of the Infinite. " I have ascended into the heavens, which receive most of His light, and I have seen things which he who descends from on high knows not, neither can repeat," wrote Dante in the first canto of his poem on " Paradise." Let us, like him, rise to- wards the celestial heights, no longer on the trembling wings of faith, but on the stronger wings of science. What the stars would teach us is incomparably more beautiful, more marvelous, and more splendid than anything we can dream of.
How do such contemplations enlarge and transfigure the vulgar idea which is generally entertained of the world! Should not the knowledge of these truths form the first basis of all instruction which aims at being serious ? Is it not strange to see the immense majority of human beings living and dying without suspecting these grandeurs, without thinking of learn- ing something of the magnificent reality which sur- rounds them?
Where the sun and his planets will journey in fu- ture ages no living man can say. Indeed, though it is a question which does not lack interest to a thought- ful mind, yet there are numberless other questions about centuries near at hand which concern man far more nearly. The history of the Universe, and the history of this Earth of ours, must have advanced many broad stages before our sun and his attendant planets can have traveled so far that any change will be apparent -in the shape of the star-constellations which spangle our sky.
CHAPTER XI.
MORE ABOUT THE SOLAR SYSTEM.
We have now reached a point where it ought not to be difficult for us to picture to ourselves, with something of vividness, the general outlines of the Solar System. Awhile ago this Solar System was a very simple matter in the eyes of astronomers. There was the great sun fixed in the center, with seven planets cir- cling round him — seven of course, it was said, since seven was the perfect number — and a few moons keep- ing pace with some of the planets, and an occasional comet, and a vast amount of black, empty space. But astronomers now begin to understand better the won- derful richness of the system as a whole; the immense variety of the bodies contained in it; the perpetual rush and stir and whirl of life in every part. Cer- tainly there is no such thing as dull stagnation throughout the family.
First, we have the great, blazing, central sun ; not a sun at rest, as regards the stars, but practically at rest as regards his own system, of which he is always head and center. Then come the four smaller plan- ets, rapidly whirling round him, all journeying in the same direction, and all having their oval pathways ly- ing on nearly the same flat plane in space. Then the broad belt of busy little planetoids. Then the four giant planets, — Jupiter nearly five times as far as our earth from the sun ; Saturn nearly twice as far as Ju-
122
MORE ABOUT THE SOLAR SYSTEM.
123
piter; Uranus nearly twice as far as Saturn; Neptune
as far from Uranus as Uranus from Saturn, — all keeping
on very nearly the same level as the four inner planets.
And between and about these principal members of
POSITION OF PLANETS INFERIOR TO JUPITER— SHOWING THE ZONE OF THE ASTEROIDS.
the system, with their accompanying moons, we have thousands of comets flashing hither and thither, with long, radiant trains ; and myriads of meteorites, gathered often into dense, vast herds or families, but also scat- tered thickly throughout every part of the system,
124 STORY OF TH£ SUN, MOON, AND STARS.
each tiny ball reflecting the sun's rays with its little glimmer of light.
Broad reaches of black and empty space ! Where are they? Perhaps nowhere. We are very apt, in our ignorance, to imagine that where we see nothing, there must of necessity be nothing. But, for aught we know, the whole Solar System, not to speak of sky-depths lying beyond, may be bright with reflect- ing bodies great and small, from the mighty Jupiter down to the fine diamond-dust of countless meteorites. In this earth of ours we find no emptiness. Closer and closer examination with the microscope only shows tinier and yet tinier wonders of form and life, each perfect in finish. Not of form only, but of life. How about that matter as regards the Solar System? Is our little world the one only spot in God's great uni- verse which teems with life? Are all other worlds mere barren, empty wastes? Surely not. We may safely conclude that life of one kind or another has been, is, or will be, upon our brother and sister worlds.
The same reasoning may be used for the distant stars — those millions of suns lying beyond reach of man's unassisted eyes. Are they formed in vain? Do their beams pour uselessly into space, carrying light, warmth, and life-giving power to nothing? Surely around many of them, as around our sun, must journey worlds ; and not only worlds, but worlds containing life.
We shall have to speak of this matter again as we go on. Whether men and women like ourselves could live on the other planets is another question. In some
MORE ABOUT THE SOLAR SYSTEM. 1 25
cases it looks doubtful, in some it would seem to be impossible. But the endless variety of life on this earth — life on land, life in the air, life in water, life underground, life in tropical heat, life in arctic cold — forbids us in anywise to be positive as to what may or may not be.
If no animals that we know could exist there, ani- mals that we do not know might be found instead. Any one of the planets may, and very likely does, abound with life. Nay, the very meteorites them- selves, before they catch fire and burn in our air, may be the homes of tiny animalcula, altogether different from anything we see on earth. We can not fancy life without air, but neither could we fancy life in water, if we had not seen and known it to be possible.
I have spoken of the probable brightness of the Solar System as a whole. We are so apt to think of things merely as we see them with our short sight, that it is well sometimes to try to realize them as they actually are. Picture to yourself the great cen- tral sun pouring out in every direction his burning rays of light. A goodly abundance of them fall on our earth, yet the whole amount of light and heat re- ceived over the whole surface of this world is only the two-thousand-millionth part of the enormous amount which he lavishly pours into space. How much of that whole is wasted? None, though God gives his gifts with a kingly profusion which knows no bounds. Each ray has its own work to do. Millions of rays are needed for the lighting and nourishing and warm- ing of our companion-planets, while others are caught up by passing comets, and myriads flash upon swift,
126 STORY OF THE SUN, MOON, AND STARS.
tiny meteorites. Of the rays not so nsed, many pass onwards into the vast depths beyond onr system, and dwindle down into dim, starlike shining till they reach the far-off brother-stars of our sun.
Have they work to do there? We can not tell. We do not know how far the sun's influence reaches. As head and center, he reigns only in his own sys- tem. As a star among stars, a peer among his equals, he may, for aught we can tell, have other work to do.
In an early chapter, mention was made of the earth's three motions, two only being explained. First, she spins ceaselessly upon her axis. So does the sun, and so do the planets. Secondly, she travels ceaselessly round and round the sun in her fixed orbit. So does each one of the planets. Thirdly, she jour- neys ceaselessly onward through space with the sun. So also do the rest of the planets. These last two movements, thought of together, make the earths pathway rather perplexing at first sight. We talk of her orbit being an ellipse or oval; but how can it be an ellipse, if she is always advancing in one direction?
The truth is, the earth's orbit is and is not an ellipse. As regards her yearly journey round the sun, roughly speaking, we may call it an ellipse. As re- gards her movement in space, it certainly is not an ellipse.
Think of the Solar System, with the orbits of all the planets, as lying nearly flat — in the manner that hoops might be laid upon a table, one within another. The asteroids, comets, and meteorites do not keep to the same level ; but their light weight makes the mat- ter of small importance.
MOR£ ABOUT THE SOLAR SYSTEM. 12/
Having imagined the sun thus in the center of a large table — a small ball, with several tiny tails trav- eling round him on the table at different distances — suppose the sun to rise slowly upwards, not directly up, but in a sharp slant, the whole body of planets continuing to travel round, and at the same time rising steadily with him.
By carefully considering this double movement, you will see that the real motion of the earth — as also of each of the planets — is not a going round on a flat surface to the same point from which she started, but is a corkscrew-like winding round and round up- wards through space. Yet as regards the central sun, the shape of the orbit comes very near being an el- lipse, if calculated simply by the earth's distance from him at each point in turn of her pathway through the year.
An illustration may help to explain this. On the deck of a moving vessel, you see a little boy walking steadily round and round the mast. Now is that child moving in a circle, or is he not? Yes, he is. No, he is not. He walks in a circle as regards the position of the mast, which remains always the center of his pathway. But his movement in space is never a circle, since he constantly advances, and does not once return to his starting-point. You see how the two facts are possible side by side. Being carried forward by the ship, with no effort of his own, the forward motion does not interfere with the circling motion. Each is performed independently of the other.
It is the same with the earth and the planets.
128 STORY OF THE SUN, MOON, AND STARS.
The sun, by force of his mighty attraction, bears them along wherever he goes — no exertion on their part, so to speak, being needed. That motion does not in the least interfere with their steady circling round the sun.
Just as — to use another illustration — the earth, turning on her axis, bears through space a man stand- ing on the Equator at the rate of one thousand miles an hour. But this uniform movement, unfelt by him- self, does not prevent his walking backwards, or for- wards, or in circles, as much as he will.
So, also, a bird in the air is unconsciously borne along with the atmosphere, yet his freedom to wheel in circles for any length of time is untouched.
A few words about the orbits of the planets. I have more than once remarked that these pathways are, in shape, not circles, but ellipses. A circle is a line drawn in the shape of a ring, every part of which is at exactly the same distance from the center-point or focus. But an ellipse, instead of being, like a circle, perfectly round, is oval in shape ; and instead of hav- ing only one focus, it has two foci, neither being ex- actly in the center. Foci is the plural word for focus. If an ellipse is only slightly oval — or slightly elliptical — the two foci are near together. The more oval or eccentric the ellipse, the farther apart are the tv/o foci.
You may draw a circle in this manner. Lay a sheet of white paper on a board, and fix a nail through the paper into the board. Then pass a loop of thread — say an inch or an inch and a half in length — round the nail, and also round a pencil, which you hold Trace a line with the pencil, keeping the loop tight,
MORE ABOUT THE SOLAR SYSTEM. 1 29
so that the distance of your line from the nail will be always equal, and when it joins you have a circle. The nail in the center is the focus of the circle.
To draw an ellipse, you must fix two nails. Let them be about half an inch apart; pass a loop over both of them, and again placing a pencil point within the loop, again trace a line carefully all round, keep- ing the thread drawn tight. This time an oval instead of a circle will appear. By putting the nails nearer together or farther apart, you may vary as you will the shape of the ellipse-.
In the orbits of the earth and the planets, all of which are ellipses in shape, the sun is not placed in the exact center, but in one of the two foci, the sec- ond being empty. So at one time of the year the planet is nearer to the sun than at another time. Our earth is no less than three millions of miles nearer in winter than she is in summer — speaking of the winter and summer of the northern hemisphere. Three mill- ions of miles is so tiny a piece out of ninety-three millions of miles, that it makes little or' no difference in our feelings of heat or cold.
The orbits of the comets are ellipses also, but ellip- ses often so enormously lengthened out, that the two foci are almost — if one may so speak — at the two ends of the oval. To draw a good comet orbit, you must fix the two nails on your paper some five or six inches apart, with a loop of thread just large enough to slip over them both, and to allow the pencil to pass round them. When your ellipse is drawn, you must picture the sun in the place of one of the two nails, and you will see how, in their pathways, the comets 9
130 story of th£ Sun, moon, and stars.
at one time pass very near the sun, and at another time travel very far away from him.
COMPARATIVE SIZE OF THE PLANETARY WORLDS.
It is generally found in families, not only that the parent or head of the family has great influence over all the members, but that each member has influence
more: about the solar system. 131
over each other member. Brother influences brother, and sister influences sister.
This, too, we find in the Solar System. Not only does the sun, by his powerful attraction, bind the whole family together, but each member of the fam- ily attracts each other member. True, the force of the sun's attraction is overpowering in amount com- pared with others. The sun attracts the planets, and the planets attract the sun ; but their feeble pulling is quite lost in the display of his tremendous strength.
Among themselves we see the power more plainly. The earth attracts the moon, keeping her in constant close attendance; and the moon attracts the earth, caus- ing a slight movement on her part, and also causing the tides of the sea. Each planet has more or less power to hinder or help forward his nearest brother-planet. For instance, when Jupiter on his orbit draws near the slower Saturn on his orbit, Saturn's attraction pulls him on, and makes him move faster than usual; but as soon as he gets ahead of Saturn then the same attraction pulls him back, and makes him go more slowly than usual. Jupiter has the same influence over Saturn ; and so also have Saturn and Uranus over one another, or Uranus and Neptune.
In early days astronomers were often greatly puz- zled by these quickened and slackened movements, which could not be explained. Now the " perturba- tions" of the planets, as they are called, are under- stood and allowed for in all calculations. Indeed, it is by means of this very attraction that Neptune was discovered, and the planets have actually been weighed. What a wonderful difference we find in this picture
132 STORY OF THE SUN, MOON, AND STARS.
of the Solar System, as we now know it to be, from the old-world notion of our earth as the center of the universe !
When we think of all the planets, and of the mag- nificent sun; when we pass onward in imagination through space, and find our sun himself merely one twinkling star amid the myriads of twinkling stars scattered broadcast through the heavens, while plan- ets and comets have sunk to nothing in the far dis- tance,— then indeed we begin to realize the unuttera- ble might of God's power! Why, our earth and all that it contains may be regarded as but one grain of dust in the wide universe.
CHAPTER XII.
MORE ABOUT THE SUN.
Not among the least of the wondrous things of creation are the tremendous disturbances taking place upon the surface of the sun — that raging, roaring sea of name.
A good many explanations have been from time to time offered as to the dark spots seen to move across the face of the sun. Some one or more of these ex- planations may be true; but we know little about the matter. A sun-spot does not commonly consist of merely one black patch. There is the dark center, called the umbra — plural, umbrcz. There is the gray- ish part surrounding the umbra, called the penumbra. Also, in the center of the umbra there is sometimes observable an intensely black spot, called the nucleus. Sometimes a spot is made up of nucleus and umbra alone, without any penumbra. Sometimes it is made of penumbra alone, without any umbra. Sometimes in one spot there are several umbrae, with the gray penumbra round the whole, and gray bridges dividing the umbrae.
The enormous size of these spots has been already described in an earlier chapter. Fifty thousand to one hundred thousand miles across is nothing unusual. In the year 1839 a spot was seen which measured no less than one hundred and eighty-six thousand miles in diameter.
133
134 STORY OF THE SUN, MOON, AND STARS.
One explanation proposed was, that trie sun might be a cool body, covered over with different envelopes or dense layers of cloudy form, one above another. The inside envelope — or, as some say, the inside at- mosphere— would then be thick and dull-colored, protecting the solid globe within and reflecting light, but having none of its own. The next envelope would be one mass of raging, burning gases — the photosphere, in fact. The outer envelope would be a transparent, surrounding atmosphere, lighted up by the sea of fire within. A sun-spot would then consist of the tearing open of one or more of these envelopes, so as to give glimpses of the gray, inner atmosphere, or even of the dark, cool globe at the center.
There may be some truth in this explanation ; but the notion of a cool and dark body within is now pretty well given up. The apparent blackness of a spot-nucleus does not prove actual blackness or ab- sence of heat. A piece of white-hot iron, held up against the sun, looks black; and it may be merely the contrast of the glowing photosphere which makes the nucleus seem so dark. It is even believed that the blackest parts may be the most intensely hot of all.
Another proposed explanation was of dark clouds floating in the sun's atmosphere. There, again, are found difficulties, particularly in the fact that, as the spots move across the sun, the changes which regu- larly take place in their appearance make it pretty clear that their shape is not flat, but hollow and cave- like. The changes here spoken of are seeming changes of shape, caused by change of position.
MORE ABOUT THE SUN.
135
There are also real changes constantly taking place. Although the spots often keep their general outlines long enough to be watched across the face of the sun, and even to be known again after spending nearly a
A TYPICAL SUN-SPOT.
fortnight hidden on the other side, still they are far from being fixed in form.
The alterations are at times not only very great, but very rapid. Sometimes in a single hour of watch- ing, an astronomer can see marked movement going
136 STORY OF THE SUN, MOON, AND STARS.
on — as you or I might in an hour observe movements slowly taking place in a high layer of clouds. For movement to show at all in one hour, at so immense a distance, proves that the actual rate of motion must be very great.
The first great fact which was got from the study of these spots was this, that this great sun is very much like our own earth, in so far as it rotates on an axis in exactly the same way that our earth does. Not only do the spots change their position on the face of the sun, in consequence of the sun's rotation on its axis, but they change very much from day to day, and even from hour to hour; so that we have evidence not only that the sun is rotating like our earth, but that the atmosphere of the sun is subjected to most tre- mendous storms — storms so tremendous, in fact, that the fiercest cyclones on our own earth are not for one moment to be compared with them. The fact that the spots do really move with the sun, and are really indentations, saucer-like hollows, in the photosphere, is shown by the appearance, which is always presented by a spot when it is near the edge of the sun. You know if you take a dinner-plate, and look it full in the face, it is round ; but if you look at it edgeways, it is not round. Take two different views of the same spot : In one, you look the sun-spot straight in the face, and you see into it and can learn all about it ; but in the other, when it has nearly gone round the corner, and is disappearing on the sun's edge, you see it in the same way that you would see a plate looked at edgeways.
These sun-cyclones must indeed be of terrific force
MORE ABOUT THE SUN. 137
and extent, compared with anything we see on earth. It was calculated that the speed of movement per- ceived in one spot was about three hundred and sixty- three miles each second.
And still all this is nothing, or almost nothing, in comparison with the real power of the sun! The liquid state of the ocean ; the gaseous state of the at- mosphere; the currents of the sea; the raising of the clouds, the rains, storms, streams, rivers; the calorific value of all the forests of the globe and all the coal- mines of the earth; the motion of all living beings; the heat of all humanity; the stored-up power in all human muscles, in all the manufactories, in all the guns, — all that is almost nothing compared with that of which the sun is capable. Do we think that we have measured the solar power by enumerating the effects which it produces on the earth? Error! profound, tremendous, foolish error ! This would be to believe still that this star has been created on purpose to illuminate terrestrial hu- manity. In reality, what an infinitesimal fraction of the sun's total radiation the earth receives and utilizes! In order to appreciate it, let us consider the distance of ninety-three millions of miles which separates us from the central star, and at this distance let us see what effect our little globe produces, what heat it in- tercepts. Let us imagine an immense sphere traced at this distance from the sun, and entirely surrounding it. Well, on this gigantic sphere, the spot intercepted by our little earth is only equivalent to the fraction 2,138,000,000 ; that is to say, that the dazzling solar hearth radiates all round it through immensity a quantity of
138 STORY OF THE SUN, MOON, AND STARS.
light and heat two thousand one hundred and thirty- eight million times more than that which we receive, and of which we have just now estimated the stupen- dous effects. The earth only stops in its passage the two thousand millionth part of the total radiation.
Sometimes the storms or outbursts come in the shape of a bright spot instead of a dark one.
A SOI,AR ERUPTION.
Two astronomers were one day watching the sun from two different observatories, when they saw such an event take place. An intense and dazzling spot of light burst out upon the surface of the sun — so in- tense, so dazzling, as to stand quite apart from the radiant photosphere. To one astronomer it looked like a single spot, while the other saw two spots close together. In about a minute the light grew more dim, and in five minutes all was over. But in those five minutes the spot or spots had traveled a distance of thirty-five thousand miles.
MORE ABOUT THK SUN. 139
It was a very remarkable thing that the magnets on earth — those delicate little needles which point so steadily yet perseveringly towards the North Pole — seemed to be strongly agitated by the distant solar outburst. This brings us to another interesting fact.
The spots on the sun are not always the same in number. Sometimes they are many, sometimes they are few. Long and close watching has made it clear that they pass through a regular order of changes: some years of many spots being followed by other years of less and less spots; then some years of very few spots being followed by other years of more and more spots, — decrease and increase being seemingly regular and alternate. <
This turn or cycle of changes — from more to less, and then from less to more again — is found to run its course about once in every eleven years, with some variations.
Now, it has long been known that the magnetic- needle goes through curious variations. Though we speak of it as pointing always north, yet it does not always so point exactly. Every day the needle is found to make certain tiny, delicate motions, as if faintly struggling to follow the daily movements of the sun — just a little towards the east, or just a little towards the west. These tiny motions, having been long watched and measured, were found to go through a regular course of changes — some years more, and some years less, waxing and waning by turns. It was discovered that the course of changes from more to less, and from less to more again, took place in about eleven years.
140 STORY OF THE) SUN, MOON, AND STARS.
These two things, you see, were quite independent of one another. Those who watched the sun-spots were not thinking of the magnets, and those who watched the magnets were not thinking of the sun- spots. But somebody did at last happen to think of both together. He was laughed at, yet he took the trouble carefully to compare the two. And, strange to say, he found that these two periods in the main agreed — the eleven years of alternate changes in the number of sun-spots, and the eleven years of alternate changes in the movements of the magnetic-needle. When the spots are most, the needle moves most. When the spots are least, the needle moves least. So much we know. But to explain the why and the wherefore is beyond our power.
This study of the magnetism of our wandering planet is very interesting, and one which is still very little known. Here is a weak needle, a slip of mag- netic iron, which, with its restless and agitated finger, incessantly seeks a region near the north. Carry this needle in a balloon up to the higher aerial regions, where human life begins to be extinguished ; shut it up in a tomb closely separated from the light of day ; take it down into the pit of a mine, to more than a thousand yards in depth, — and incessantly, day and night, without fatigue and without rest, it watches, trembles, throbs, seeks the point which attracts it across the sky, through the earth, and through the night. Now — and here is a coincidence truly filled with notes of interrogation — ■ the years when the oscillation of this innocent little steel wire is strongest are the years when there are more spots, more eruptions, more tempests in the sun ;
MORH ABOUT THE SUN. 141
and the years when its daily fluctuations are weakest are those when we see in the day-star neither spots, eruptions, nor storms. Does there exist, then, a mag- netic bond between the immense solar globe and our wandering abode? Is the sun magnetic? But the magnetic currents disappear at the temperature of red- hot iron, and the incandescent focus of light is at a temperature incomparably higher still. Is it an elec- trical influx which is transmitted from the sun to the earth across a space of ninety-three millions of miles? On September 1, 1859, two astronomers — Carring- ton and Hodgson— were observing the sun, independ- ently of each other; the first on a screen which received the image ; the second directly through a tele- scope,— when, in a moment, a dazzling flash blazed out in the midst of a group of spots. This light sparkled for five minutes above the spots without modifying their form, as if it were completely independent, and yet it must have been the effect of a terrible confla- gration occurring in the solar atmosphere. Each ob- server ascertained the fact separately, and was for an instant dazzled. Now, here is a surprising coincidence : at the very moment when the sun appeared inflamed in this region the magnetic instruments of the Kew Observatory, near London, where they were observ- ing, manifested a strange agitation; the magnetic needle jumped for more than an hour as if infatuated. Moreover, a part of the world was on that day and the following one enveloped in the fires of an aurora borealis, in Europe as well as in America. It was seen almost everywhere, — at Rome, at Calcutta, in Cuba, in Australia, and in South America. Violent
142 STORY OF THE SUN, MOON, AND STARS.
magnetic perturbations were manifested, and at sev- eral points the telegraph-lines ceased to act. Why should these two curious events not be associated with each other? A similar coincidence was observed on August 3, 1872, by Professor Charles A. Young, of Princeton, N. J. : a paroxysm in the solar chromo- sphere, magnetic disturbances everywhere.
There is a very singular appearance seen upon the sun which must not be passed over without mention. Some astronomers speak of the whole surface as being mottled all over with a curious rough look when exam- ined through a powerful telescope. This "mottling" is described by various observers in various ways. One speaks of "luminous spots shaped like rice- grains." Another, of "luminous spots resembling strokes made with a camePs-hair pencil." Another, of "luminous objects or granules." Others, of "mul- titudes of leaves," "nodules," "crystalline shapes," "leaves or scales, crossing one another in all direc- tions, like what are called spills in the game of spilli- kens." They have also been pictured as "certain luminous objects of an exceedingly definite shape and general uniformity of size, whose form is that of the oblong leaves of a willow- tree." These cover the whole disk of the sun, excepting the space occupied by the spots, in countless millions, and lie crossing each other in every imaginable direction.
In size they are said to be about one thousand miles long, by two or three hundred broad, but they vary a good deal. Where there is a spot, the willow-leaves at its edge are said to point pretty regularly towards the center. Whether they are, as they seem to be,
MORE ABOUT THE SUN.
143
solid in form ; whether they are, as some suppose, the chief source of the sun's light and heat ; whether they lie on his surface or float in his atmosphere; what is their real nature, and what is their real use, — about these questions we are at present quite in the dark.
We have next to think a little more about the edge or limb of the sun, and the stormy flames and out- burst there seen. Until quite lately the only time for observing such ap- pearances was dur- ing a total eclipse of the sun. Lately, by means of the new instrument called the " spectro- scope," it has been found possible to take observations when no eclipse is going on.
A few words of explanation as to eclipses of the sun seem needful, before going further. An eclipse of the sun is caused simply by the round body of the moon passing exactly between the sun and the earth, so as to hide the sun from us.
Let there be a candle on the table, while you stand near. The rays of light from the candle fall upon your face. Now move slowly, to and fro, a round ball
SUN-FLAMES, MAY 3, 1892.
144 story of the: sun, moon, and stars.
between you and the candle. So long as it is not pre- cisely in the line between — so long as it is a little higher, or a little lower, or a little to one side — then yon can still see the flame. Once let the ball come just between the light and your eyes, and you see it no more. In other words the candle-flame is eclipsed — hidden, veiled, cut off — by the ball.
It may seem curious at first sight that the moon, which is very small compared with the sun, should have power to cover the sun. But remember the dif- ference of the distance. The sun is very far, and the moon is very near. Any small object very near will easily hide from your sight a large object at a con- siderable distance. You may hold up a shilling-piece at arm's length, and make it cover from sight a man, or even a house, if the latter be far enough away. The sun at a distance of ninety-three millions of miles, and the moon at a distance of two hundred and forty thousand miles, have to our vision the same seeming size. So, when the moon glides between, her round face just about covers the sun's round face.
If the moon were traveling exactly in the same plane as the plane of the earth's orbit, an eclipse would be a very common affair indeed. But the plane of the moon's orbit being not quite the same as the plane of the earth's orbit, she passes sometimes a little above, and sometimes a little below, the exact spot where she would hide the sun's rays from us. Now and then, at certain intervals, she goes just between. And so well is the moon's path in the heavens understood that astronomers can tell us, long years beforehand, the day and the hour an eclipse will take place.
MORE ABOUT THE SUN. 145
An eclipse of the sun is sometimes partial, some- times total, sometimes annular. In a partial eclipse, the moon does indeed pass between, but only so as to hide from us part of the sun. She is a little too low, or a little too high, to cover his face. In a total eclipse, the moon covers the sun completely, so that for a few minutes the bright photosphere seems blot- ted out from the heavens, a black round body, sur- rounded by light, taking its place. In an annular eclipse, the moon in like manner crosses the sun, but does not succeed in covering him entirely, a rim of bright photosphere showing round the black moon. For in an annular eclipse, the moon, being a little farther away from the earth than at the time of a total eclipse, has too small a disk quite to hide the sun's disk.
The blackness of the moon during an eclipse is caused by the fact that her bright side is turned to- wards the sun, and her dark side toward us. An eclipse of the sun can take place only at new moon, never at full moon. At her full, the moon is outside the earth's orbit, away from the sun, and can not by any possibility pass between.
Eclipses, like comets, have always been inter- preted as the indication of inevitable calamities. Human vanity sees the finger of God making signs to us on the least pretext, as if we were the end and aim of universal creation. Let us mention, for ex- ample, what passed even in France, with reference to the announcement of an eclipse of the sun, on August 21, 1560. For one, it presaged a great overthrow of States and the ruin of Rome; for another, it implied
I46 STORY OF THK SUN, MOON, AND STARS.
another universal deluge; for a third, nothing less would result than a conflagration of the globe ; finally, for the less excited, it would infect the air. The be- lief in these terrible effects was so general that, by the express order of the doctors, a multitude of fright- ened people shut themselves up in very close cellars, well heated and perfumed, in order to shelter them- selves from these evil influences. Petit relates that the decisive moment approached, that the consterna- tion was at its height, and that a parish priest of the country, being no longer able to confess his parish- ioners, who believed their last hour had come, was obliged to tell them in a sermon " not to be so much hurried, seeing that, on account of the wealth of the penitents, the eclipse had been postponed for a fort- night." These good parishioners found no more diffi- culty in believing in the postponement of the eclipse than they had in believing in its unlucky influence.
History relates a crowd of memorable acts on which eclipses have had the greatest influence. Alexander, before the battle of Arbela, expected to see his army routed by the appearance of a phenomenon of this kind. The death of the Athenian general Nicias and the ruin of his army in Sicily, with which the decline of the Athenians commenced, had for their cause an eclipse of the moon. We know how Christopher Co- lumbus, with his little army, threatened with death by famine at Jamaica, found means of procuring provis- ions from the natives by depriving them in the evening of the light of the moon. The eclipse had scarcely commenced when they supplied him with food. This was the eclipse of March 1, 1504. We need not relate
MORE ABOUT THE SUN. 147
other facts of this nature, in which history abounds, and which are known to every one.
Eclipses no longer cause terror to any one, since we know that they are a natural and inevitable conse- quence of the combined motions of the three great celestial bodies — the sun, the earth, and the moon; especially since we know that these motions are reg- ular and permanent, and that we can predict, by means of calculation, the eclipses which will be produced in the future as well as recognize those which have oc- curred in the past.
The following description of the total eclipse of i860 will be found interesting. Mr. Lowe, who ob- served it at Santander, Spain, thus writes :
" Before totality commenced, the colors in the sky and on the hills were magnificent beyond all descrip- tion. The clear sky in the north assumed a deep indigo color, while in the west the horizon was first black like night. In the east the clear sky was very pale blue, with orange and red, like sunrise. On the shadow creeping across, the deep blue in the north changed, like magic, to pale, sunrise tints of orange and red, while the sunrise appearance in the east had changed to indigo. The darkness was great; the countenances of men were of a livid pink. The Spaniards lay down, and their children screamed with fear; fowls hastened to roost, ducks clustered to- gether, pigeons dashed against the houses; flowers closed; many butterflies flew as if drunk, and at last disappeared. The air became very humid, so much so that the grass felt to one of the observers as if re- cently rained upon."
CHAPTER XIII.
YET MORE ABOUT THE SUN.
Having seen something of storms taking place on the sun's photosphere, we must next give our atten- tion to storms taking place at his edge. But it should be remembered that the said edge, far from being a mere rim to a flat surface, is a kind of horizon-line— is, in fact, just that part of the photosphere which is passing out of or coming under our sight. The sur- face there is, in kind, the same as the surface of the broad disk facing us. In watching outbursts at the edge of the sun, we have a side view instead of a bird's-eye view.
In the year 187 1, Professor Charles A. Young, of Princeton, was looking at a large hydrogen cloud on the edge of the sun. When I speak of a "cloud," it must not be supposed that anything like a damp, foggy, earthly cloud is meant. This solar cloud was a huge mass of red-hot gas, about one hundred thou- sand miles long, rising to a height of fifty thousand miles from the sun's surface, and appearing to rest on glowing pillars of fire.
The professor, while watching, was called away for half an hour. He came back, expecting to find things much as he had left them. Instead of this, a start- ling change had taken place. The whole mass of glowing fire seemed to have been actually " blown to shreds" by some tremendous outburst from below.
148
YET MORE ABOUT THE SUN. 1 49
In place of the motionless cloud were masses of scat- tered fire, each from about four thousand to fourteen thousand miles long, and a thousand miles wide.
As the professor gazed, these "bits" of broken cloud rose rapidly upwards, away from the surface of the sun. When I say "rapidly," I mean that the real movement, which the professor could calculate, was rapid. The seeming movements were of course slow, and over a small space. The actual motions were not tardy, for in ten minutes these huge, fiery cloud-pieces rushed upwards to a height of two hundred thousand miles from the edge of the sun, moving at a rate of at least one hundred and sixty-seven miles each second. Gradually they faded away.
But what caused this sudden change? Just before the professor was interrupted, he had noticed a curi- ous little brilliant lump — a sort of suspicious thunder- cloud appearance — below the quiet, bright cloud. And after this tremendous shattering, the little bright lump rose upwards into a huge mass of rolling flame, reach- ing like a pyramid to a height of fifty thousand miles. In the course of a few minutes these enormous flames could be seen to move and bend, and to curl over their gigantic tips. But they did not last long. At half- past twelve the professor had been called away; by half-past two the rolling flames completely vanished.
Now, whatever may be the full explanation of this sight, there is no doubt that on that day was observed from earth a tremendous outburst, compared with which our mightiest volcanoes are like the sputtering of a farthing dip beside a roaring furnace. The aw- ful force and greatness of such a solar eruption are
150 STORY OF THE SUN, MOON, AND STARS.
more than we can possibly picture to ourselves. At our distance we may catch a faint glimpse of what is going on, and calculate speed of movement. But vividly to realize the actual terrific grandeur of what took place is past our power.
Possibly this was much the same kind of outburst as that seen by the two English astronomers; only theirs was a bird's-eye view, as it were, looking down on the top of the sight, while the professor had a side- view, certainly much the best for observation.
It does not follow from what he saw that the erup- tion must have taken place exactly at the "edge" of the sun. Probably it happened near the edge. All he could say, was that the flames rose fifty thousand miles, and the pieces of cloud were carried two hun- dred thousand miles, away from the edge. The erup- tion may have begun on the other side of the sun, at any distance from the horizon-edge where it first be- came visible to earthly eyes.
Also, while the professor found that the shattered cloudlets moved at a rate of about one hundred and sixty-seven miles each second, it is calculated that the first fearful outburst must have caused movement, near the surface of the sun, at a rate of at least three hundred miles each second. Probably the hydrogen cloud was borne upwards along with a vast mass of fragments flung out from the sun. We are here upon doubtful ground; but this tremendous power of erup- tion in the sun, and of driving matter out of and away from his surface, should not be forgotten.
Though such a sun-storm as that just described is not often to be seen, yet there are at all times certain
YET MORE ABOUT THE SUN. 151
strange red prominences, or glowing flames, rising up here and there from the sun's " limb." Doubtless they rise also from other parts of the photosphere, though they are only visible to us when near enough to the edge to stand out beyond it.
Seen during an eclipse, these prominences have clear, sharp outlines, and are usually bright rose-red in color. They are described as sometimes wide and low, sometimes tall and slender; sometimes jagged, sometimes regular; sometimes keeping long the same shape, sometimes changing quickly in a few minutes. They are said to be like flames, like mountains, like the teeth of a saw, like icebergs, like floating cloud- lets.
As to their height, from fifty to eighty thousand miles is nothing unusual. We must not speak of Mont Blanc or Mount Everest here. Jupiter placed bodily on the surface of the sun, beside such a fire- mountain, would not far overtop it. The earth, Venus, Mars, and Mercury, would lie like little toy-balls at its foot. And these are common-sized sun-flames. One was measured which reached to the enormous height of two hundred thousand miles. The spectroscope shows these solar prominences or jets to be made — at least in part — of burning hydrogen gas.
Beyond the sierra or chromatosphere — that border of rippling, crimson flame-billows round the edge of the sun, with red flame-mountains rising out of it here and there — beyond these, stretches the corona. The corona, as seen from earth, is a bright, far-reach- ing glory of light, shining round the sun in a total eclipse. The moon then comes between he sun and
152 STORY OK THE) SUN, MOON, AND STARS.
the earth, her dark, round body creeping over the face of the sun till the bright photosphere is completely covered. But the sierra and the tall, red flames stand out from behind the black moon, and the beautiful, soft corona-light stretches far beyond.
SOLAR CORONA AND PROMINENCE.
It was long doubted whether the corona really be- longed to the sun or to the moon. There seems now no doubt that it is a part of the sun.
Various descriptions of the corona have been given at different times, as observed during different
YET MORE ABOUT THE SUN. 1 53
eclipses. It has been seen as a steady, beamy, white cloud behind the moon, showing no flickering. It has been seen marked with bright lines of light, and seem- ing to move rapidly round and round. It has been seen silvery white, sending off long streams of bright- ness. It has been seen in the form of white light, with bluish rays running over it. It has been seen with entangled jets of light, like "a hank of thread in disorder." It has been seen silvery- white again, with a faint tinge of greenish-violet about the outer edge. It has been seen from a high mountain-top as a mass of soft, bright light, "through which shot out, as if from the circumference of the moon, straight, massive, silvery rays, seeming distinct and separate from each other, to a distance of two or three diameters of the lunar disk, the whole spectacle showing as upon a background of diffused, rose-colored light."
Majestic, indeed, are the proportions of some of those mighty flames which leap from the surface of the sun, yet these flames nicker, as do our terrestrial flames, when we allow them time comparable to their gigantic dimensions. Drawings of the same promi- nence often show great changes in a few hours, or even less. The magnitude of the changes could not be less than many thousands of miles, and the actual velocity with which such masses move is often not less than one hundred miles a second. Still more violent are the solar convulsions, which some observers have been so fortunate as to behold, when from the sun's surface, as from a mighty furnace, vast incandescent masses are projected upwards. All indications point to the surface of the sun as the seat of the most frightful
154 STORY OF THE SUN, MOON, AND STARS.
storms and tempests, in which the winds sweep along incandescent vapors.
The corona consists of two parts — the inner and brighter corona, the onter and fainter corona. The shape of the whole seems to change much at different times. The outer edge is usually blurred and indis- tinct, fading gently away.
Many explanations have been suggested. At one time the corona was supposed to be a solar atmos- phere, reflecting light like our own atmosphere. Some have thought the light might be caused by countless myriads of meteorite systems, revolving in the close neighborhood of the sun. Some suppose it may be owing, in part at least, to solar eruptions, and the pouring outward of burning gas and matter. But our knowledge of the true nature of the corona is yet in its infancy.
A few closing words as to the size and weight of the sun. In diameter, eight hundred and fifty-eight thousand miles, and in bulk equal to one million two hundred and eighty thousand earths, his weight is in proportion less. Our earth is about four times as dense as the sun. If her size were increased to the sun's size, her density being the same as now, she would be very much heavier than the sun, and would attract much more strongly. Still, though the sun is of lighter materials than the earth, his immense size gives him weight equal to seven hundred and fifty times as much as all the planets put together.
The attraction on the surface of the sun is also very great — so great that we can hardly picture it to ourselves. If life exists there at all — supposing it
YET MORE ABOUT THE SUN. 1 55
possible that any kind of life can be in such a fiery atmosphere — it must be life very different from any known in this world. A man who on earth weighs one hundred and sixty pounds, and walks lightly erect, would, on the sun, lie helplessly bound to the ground, crushed by his own overpowering weight. It is said that a cannon-ball, reposing on the sun, if lifted one
COMPARATIVE SIZE OF THE EARTH AND SUN.
inch and allowed to fall, would dash against the ground with a speed three times greater than that of our fastest express-trains. For weight on earth is merely caused by the amount of force with which the earth draws downward a body towards herself — a force greater or less according to the density of that body. So weight on the sun would be immensely increased by his immensely greater power of at- traction.
I56 STORY OF THE SUN, MOON, AND STARS.
It is an interesting question how far the sun's at- tractive influence reaches effectually through space. The nearer a body is to the sun, the greater the at- traction which he exercises over it. At the distance of the planet Mercury, a speed of twenty-nine miles each second is needful to overcome or balance it suffi- ciently for the planet to remain in his orbit. At the distance of the planet Neptune, about three miles each second is enough. If a planet were journeying at four times the distance of Neptune, the speed would need to be not over two miles each second, lest the planet should break loose and wander away. But even two miles a second is no mean speed — more than seven thousand miles an hour. If we come to speak of that which we on earth call rapid motion, we shall gain a clearer idea as to the extent of the sun's power.
Suppose a planet were traveling through space at the rate of one of our fastest express-trains — sixty miles an hour. It has been calculated that, unless the sun's attraction were interfered with and over- powered by some nearer sun, the said planet, though placed at a distance ten or twelve times as great as that of the far-off star Alpha Centauri, would still be forced by the sun's attraction to journey round him in a closed orbit. At such a speed it would not be free to wander off into the depths of space.
CHAPTER XIV.
MORE ABOUT THE MOON.
From a globe all fire, all energy, all action, we come to a globe silent, voiceless, changeless, lifeless. So, at least, the moon seems to us. But it will not do to speak too confidently.
True, we can find no trace of an atmosphere in the moon. If there is any atmosphere at all, it must be so thin as to be less than that which we on earth count as actually none. We pump away the air from a glass inclosure in an air-pump, and say the glass is empty. Only it is not quite empty. There is al- ways just a very little air remaining, though so little that fire would not burn and animals could not live in it. Some believe that air, up to that amount, may be found in the moon. But this is much the same as to .say there is none at all. For, of course, with either no air or so very little air, life can not possibly exist on the moon. We can not imagine such a thing for a moment. That is just how the matter stands. We " can not imagine," and therefore we conclude it to be an impossibility. As if we knew a hundredth part of the possibilities in any one corner of God's great uni- verse! As if our being unable to picture a thing proves that thing not to exist !
Suppose we had always lived in tropical heat, and had never seen, known, or heard of such a fact as life in Arctic snows. Should we consider it a thing pos- • 157
I58 STORY OF THE SUN, MOON, AND STARS.
sible ? Suppose we had always lived on dry land, with never a sight of sea or river or pond, and never a proof that animal life could exist under water — aye, and that some living animals may be suffocated by air, just as other living animals are suffocated by water. Should we not, in our wisdom, reason out such a state of affairs to be utterly impossible?
There may be no life on the moon. Jt may be that she is now passing through a dead, cold, blasted stage, either at the close of some past history, or in prepara- tion for some future history — or both. But, on the other hand, it may be that the moon is no less full of life than the earth; only the life must be different in kind, must be something which we do not know any thing at all about.
The moon is very much smaller than the earth. Her diameter is about two-sevenths of the earth's di- ameter; her entire surface is about two twenty-sev- enths of the earth's surface ; her size is about two ninety-ninths of the earth's size ; and her whole weight is about one-eightieth of the earth's weight. Attrac- tion or gravitation on the surface of the moon is very different from what it is on the earth. Her much smaller bulk greatly lessens her power of attraction. While a man from earth would, on the surface of the sun — supposing he could exist there at all— lie helpless, motionless, and crushed by his own weight, he would on the moon find himself astonishingly light and active. A leap over a tall house would be noth- ing to him.
The moon, unlike the sun, has no light or heat of her own to give out. She shines merely by reflected
MORE ABOUT THE MOON.
159
light. Rays of sunlight falling upon her, rebound thence, and find their way earthward. This giving of
THE MOON — AN EXPIRED PLANET.
reflected light is not a matter all on one side. We yield to the moon a great deal more than she yields to us. Full earth, seen from the moon, covers a
l6o STORY OF THE SUN, MOON, AND STARS.
space thirteen times as large as full moon seen from earth.
Perhaps you may have noticed, soon after new moon, when a delicate crescent of silver light shows in the sky, that within the said crescent seems to lie the body of a round, dark moon, only not perfectly dark. It shows a faint glimmer. That glimmer is called earth-shine. The bright crescent shines with reflected sunlight. The dim portion shines with re- flected earth-light. What a journey those rays have had! First, leaving the sun, flashing through ninety- three millions of miles to earth, rebounding from earth and flashing over two hundred and forty thousand miles to the dark shaded part of the moon, then once more rebounding and coming back, much wasted and enfeebled, across the same two hundred and forty thousand miles, to shine dimly in your eyes and mine. The popular description of this particular view of the moon is " the old moon in the arms of the new."
Now about the phases of the moon ; that is, her changes from "new" to "full," and back again to "new." If the moon were a starlike body, shining by her own light, she would always appear to be round. But as she shines by reflected sunlight, and as part of her bright side is often turned away from us, the size and shape of the bright part seem to vary. For, of, course, only that half of the moon which is turned directly towards the sun is bright. The other half turned away is dark, and can give out no light at all, unless it has a little earth-shine to reflect.
As the moon travels round the earth, she changes gradually from new to full moon, and then back to
MORE ABOUT THE MOON. l6l
new again. "New moon" is when the moon, in her orbit, comes between the sun and the earth. The half of her upon which the sun shines is turned away from us, and only her dark side is towards us. So at new moon she is quite invisible. It is at new moon that an eclipse of the sun takes place, when the moon's orbit carries her in a line precisely between sun and earth.
Passing onwards round the earth, the moon, as we get a little glimpse of her shining side, first shows a slender sickle of light, which widens more and more till she reaches her first quarter. She is then neither between earth and sun, nor outside the earth away from the sun, but just at one side of us, passing over the earth's own orbit. Still, as before, half her body is lighted up by the sun. By this time half the bright part and half the dark part are turned towards us; so that, seeing the bright quarter, we name it the ' ' first quarter."
On and on round us moves the moon, showing more light at every step. Now she passes quite out- side the earth's orbit, away from the sun. Not the slightest chance here of an eclipse of the sun, though an eclipse of the moon herself is quite possible. But more of that presently. As she reaches a point in a line with earth and sun — only generally a little higher or lower than the plane of the earth's orbit — her round, bright face, shining in the sun's rays, is turned exactly towards us. Then we have "full moon."
Still she goes on. Once more her light narrows and wanes, as part of her bright half turns away. Again at the "last quarter," as at the first, she occu-
1 62 STORY OF THE SUN, MOON, AND STARS.
pies a "sideways" position, turning towards us half her bright side and half her dark side. Then she journeys on, with lessening rim of light, till it van- ishes, and once more we have the dark, invisible "new moon."
It was these phases and aspects of the moon which formerly gave birth to the custom of measuring time by months, and by weeks of seven days, on account of the return of the moon's phases in a month, and be- cause the moon appears about every seven days, so to say, under a new form. Such was the first measure of time ; there was not in the sky any signal of which the differences, the alternations, and the epochs were more remarkable. Families met together at a time fixed by some lunar phase.
The new moons served to regulate assemblies, sac- rifices, and public functions. The ancients counted the moon from the day they first perceived it. In or- der to discover it easily, they assembled at evening upon the heights. The first appearance of the lunar crescent was watched with care, reported by the high priest, and announced to the people by the sound of trumpets. The new moons which correspond with the renewal of the four seasons were the most solemn ; we find here the origin of the "ember weeks" of the Church, as we find that of most of our festivals in the ceremonies of the ancients. The Orientals, the Chal- deans, Egyptians, and Jews religiously observed this custom.
An eclipse of the sun has already been described. An eclipse of the moon is an equally simple matter. An eclipse of the sun is caused by the dark, solid
MORE ABOUT THE MOON. 163
body of the moon passing just between earth and sun, hiding the sun from us, and casting its shadow upon the earth. An eclipse of the moon is also caused by a shadow — the shadow of our own earth — falling upon the moon.
Here again, if the plane of the moon's orbit were the same as ours, eclipses of the moon would be very common. As it is, her orbit carries her often just a little too high or too low to be eclipsed, and it is only now and then, at regular intervals, that she passes through the shadow of the earth.
If a large, solid ball is hung up in the air, with bright sunlight shining on it, the sunlight will cast a cone of shadow behind the ball. It will throw, in a direction just away from the sun, a long, round shadow, the same as the ball at first, but tapering gradually off to a point. If the ball is near the ground, a round shadow will rest there, almost as large as the ball. The higher the ball is placed, the smaller will be the round shadow, till at length, if the ball be taken far enough upwards, the shadow will not reach the ground at all. Our earth and all the planets cast just such tapering cones of dark shadow behind them into space. The cone always lies in a direction away from the sun.
It is when the moon comes into this shadow that an "eclipse of the moon" takes place. Sometimes she only dips half-way into it, or just grazes along the edge of it, and that is called a "partial eclipse." Sometimes she goes in altogether, straight through the midst of the shadow, so that the whole of her bright face for a short time grows quite dark. Then we have a "total lunar eclipse."
CHAPTER XV.
YET MORE ABOUT THE MOON.
There are two ways of thinking abont the moon. One way is to consider her as merely the earth's attendant satellite. The other wTay is to consider her as our sister-planet, traveling with us round the central sun.
The first is the more common view ; but the second is just as true as the first.
For the sun does actually pull the moon towards himself, with a very much stronger pulling than that of the earth. The attraction of the sun for the moon is more than double the attraction of the earth for the moon. If it were not that he pulls the earth quite as hard as he pulls the moon, he would soon overpower the earth's attraction, and drag the moon away from us altogether.
People are often puzzled about the orbit or path- way of the moon through the heavens. For in one sense they have to think of her as traveling round and round in a fixed orbit, with the earth in the center. In another sense they have to think of her as always journeying onwards with the earth in her journey round the sun, and thus never returning to the same point.
There are two ways of meeting this difficulty. First of all, remember that the one movement does not interfere with the other. Just as in the case of
164
YET MORE ABOUT THE MOON. 165
the earth traveling round the sun, and also traveling onward with him through space ; just as in the case of a boy walking round and round a mast, and also being borne onwards by the moving vessel, — so it is here. The two movements are quite separate and independent of each other. As regards the earth alone, the moon journeys round and round perpet- ually, not in a circle, but in a pathway which comes near being an ellipse. As regards the actual line which the moon's movements may be supposed to draw in space, it has nothing elliptical about it, since no one point of it is ever reached a second time by the moon.
But according to this last view of the question, no- body ever can or will walk in a circle or an oval. Take a walk round your grass-plot, measuring your distance carefully at all points from the center. Is that a circle ? All the while you moved, the surface of the earth was rushing along and bearing you with it, and the whole earth was hurrying round the sun, and was being also carried by him in a third direc- tion. Whatever point in space you occupied when you started, you can never fill that particular part of space again. The two ends of your so-called circle can never be joined.
But then you may come back to the same point on the grass, as that from which you started. And this is all that really signifies. Practically you have walked in a circle. Though not a circle as regards space generally, it is a circle as regards the earth. So also the moon comes back to the same point in her orbit round the earth. Letting alone the question
1 66 STORY OF the: sun, moon, and stars.
of space, and considering only the earth, the moon has — roughly speaking — journeyed in an ellipse. You may, however, look at this matter in quite an- other light. Forget about the moon being the earth's satellite, and think of earth and moon as two sister- planets going round the sun in company.
The earth, it is true, attracts the moon. So, also, the moon attracts the earth ; though the far greater weight of the earth makes her attraction to be far greater. If earth and moon were of the same size, they would puil each other with equal force.
But though the pull of the earth upon the moon is strong, the pull of the sun upon the moon is more than twice as strong. And greatly as the earth influ- ences the moon, yet the actual center of the moon's orbit is the sun, and not the earth. Just as the earth travels round the sun, so also the moon travels round the sun.
The earth travels steadily in her path, being only a little swayed and disturbed by the attraction of the moon. The moon on the contrary, while traveling in her orbit, is very much swayed and disturbed in- deed by the earth's attraction. In fact, instead of being able to journey straight onwards like the earth, her orbit is made up of a succession of delicate curves or scallops, passing alternately backwards and forwards over the orbit of the earth. Now she is behind the earth ; now in front of the earth ; now between earth and sun; now outside the earth away from the sun. The order of positions is not as here given, but each is occupied by her in turn. Sometimes she moves quickly, sometimes she moves slowly, just according
YET MORE ABOUT THE MOON. 167
to whether the earth is pulling her on or holding her back. Two hundred and forty thousand miles sounds a good deal. That is the distance between earth and moon. But it is, after all, a mere nothing, compared with the ninety-three millions of miles which separate the sun from the earth and moon.
If we made a small model, with the sun in the center, and the earth and moon traveling a few inches off, only one slender piece of wire would be needed to represent the path of earth and moon together. For not only would the earth and the moon be so small as to be quite invisible, but the whole of the moon's orbit would have disappeared into the thick- ness of the single wire. This question of the moon's motions is in its nature intricate, and in its details quite beyond the grasp of any beginner in astronomy. But so much at least may be understood, that though the earth's attraction powerfully affects the moon, and causes in her motions pertnrbatio7is, such as have been already spoken about as taking place among the planets, yet that in reality the great controlling power over the moon is the attraction of the sun.
The tides of the ocean are chiefly brought about by the moon's attraction. The sun has something to do with the matter, but the moon is the chief agent. This action of the moon can best be seen in the south- ern hemisphere, where there is less land. As the moon travels slowly round the earth, her attraction draws up the yielding waters of the ocean in a vast wave which travels slowly along with her. The same pulling which thus lifts a wave on the side of the earth towards the moon, also pulls the earth gently
l68 STORY OF THE SUN, MOON, AND STARS.
away from the water on the opposite side, and causes a second wave there. The parts of the ocean between these two huge waves are depressed, or lower in level. These two waves on the opposite sides of the earth sweep steadily onwards, following the moon's move- ments,— not real, but seeming movements, caused by the turning of the earth upon her axis.
Once in every twenty-four hours these wide waves sweep round the whole earth in the southern ocean. They can not do the same in the north, on account of the large continents, but offshoots from the south waves travel northwards, bringing high-tide into every sea and ocean inlet. If there were only one wave, there would be only one tide in each twenty-four hours. As there are two waves, there are two tides, one twelve hours after the other. In the space be- tween these two high-tides we have low-tide.
Twice every month we have very high and very low tides. Twice every month we have tides not so high or so low. The highest are called " spring- tides," and the lowest "neap-tides." When the moon is between us and the sun, or when she is "new moon," there are spring-tides; for the pull or attraction of sun and moon upon the ocean act exactly together. It is the same at full moon, when once more the moon is in a straight line with earth and sun. But at the first and last quarters, when the moon has her sideways posi- tion, and when the sun pulls in one direction and the moon pulls in another, each undoes a little of the other's work. Then we only have neap-tides ; for the wave raised is smaller, and the water does not flow so high upon our shores.
YET MORE ABOUT THE MOON. 169
In speaking of the surface of the moon, we are able only to speak about one side. The other is entirely hidden from us. This is caused by the curious fact that the moon turns on her axis and travels round the earth in exactly the same length of time. One-half of the moon is thus always turned to- wards us, though of that half we can only see so much as is receiving the light of the *sun. But the half turned in our direction is always the same half. One part of the moon — not quite so much as half, though always the same portion — is turned away from us. A small border on each side of that part becomes now and then visible to us, owing to certain move- ments of the earth and the moon.
What sort of a landscape may lie in the unknown district, it is idle to imagine. Many guesses have been made. Some have supposed it possible that air might be found there ; that water might exist there ; that something like earthly animals might live there. It is difficult to say what may not be, in a place about which we know nothing whatever. But judging from our earthly experience, nothing seems more unlikely than that air, water, clouds, should be entirely ban- ished from over one-half of a globe, and collected to- gether in the space remaining.
We are on safer ground when we speak about that part of the moon which is turned towards us. For we can say with confidence that if any atmosphere exist there, it must be in thickness less than the two-thou- sandth part of our earthly atmosphere. It seems equally clear that water also must be entirely wanting. The tremendous heat of the long lunar day would
170 STORY OF THE SUN, MOON, AND STARS.
raise clouds of vapor, which could not fail to be visible. But no such mistiness ever disturbs the sharply-defined outline of the moon, and no signs of water action are seen in the craggy mountains and deep craters.
The craters which honeycomb the surface of the
THE EUNAR CRATER COPERNICUS.
moon are various in size. Many of the larger ones are from fifty to a hundred miles in diameter. These huge craters — or, as we may call them, deep circular plains — are surrounded by mighty mountain ram- parts, rising to the height of thousands of feet. Usually they have in their center a sugar-loaf or
YET MORE ABOUT THE MOON. 171
cone-shape mountain, or even two or more such mountains, somewhat lower in height than the sur- rounding range. The sunset-lights upon certain of these distant mountain-peaks were first watched by Galileo through his telescope, and have since been seen by many an observer — intense brightness con- trasting with intense blackness of shadow.
In addition to her great craters, the moon seems to be thickly covered with little ones, many of them being as small as can be seen at all through a telescope. Whether these are all volcano-craters remains to be discovered. It is not supposed that any of them are now active. From time to time, signs of faint changes on the moon's surface have been noticed, which it was thought might be owing to volcanic outbursts. Such an outburst as the worst eruptions of Mount Vesuvius would be invisible at this distance. But the said changes may be quite as well accounted for by the startling fortnightly variations of climate which the moon has to endure. The general belief now in- clines to the idea that the moon-volcanoes are extinct, though no doubt there was in the past great volcanic activity there.
A description has been given earlier of the rain of meteorites constantly falling to our earth, and only prevented by the atmosphere from becoming serious. But the moon has no such protecting atmosphere, and the amount of cannonading which she has to endure must be by no means small. Perhaps in past times, when her slowly-cooling crust was yet soft, these ce- lestial missiles showering upon her may have occa- sionally made deep round holes in her surface.
172 STORY OF THE SUN, MOON, AND STARS.
This is another guess, which time may prove to be true. Guesses at possible explanations of mysteries do no harm, so long as we do not accept them for truth without ample reason.
The origin of the lunar craters must be referred to some ancient epoch in the moon's history. How ancient that epoch is we have no means of knowing;
I,UNAR ERUPTION — BRISK ACTION.
but in all probability the antiquity of the lunar craters is enormously great. At the time when the moon was sufficiently heated to have these vast volcanic eruptions, of which the mighty craters are the sur- vivals, the earth must have been ver}' much hotter than it is at present. It is not, indeed, at all unrea- sonable to believe that when the moon was hot enough for its volcanoes to be active, the earth was so hot that life was impossible on its surface. This supposition
YET MORE ABOUT THE MOON.
173
would point to an antiquity for the moon's craters far too great to be estimated by the centuries and the thousands of years which are adequate for the lapse of time as recognized by the history of human events. It seems not unlikely that millions of years may have elapsed since the mighty craters of Plato or of Coper- nicus consolidated into their present form.
LUNAR ERUPTION— FEEBLE ACTION.
It will now be possible for us to attempt to ac- count for the formation of the lunar craters. The most probable views on the subject are certainly those adopted by Mr. Nasmyth, as represented in the cuts, though it must be admitted that they are by no means free from difficulty. We can explain the way in which the rampart around the lunar crater is formed, and the great mountain which so often adorns the center of the plain. The first of these cuts contains an im-
174 STORY OF THE SUN, MOON, AND STARS.
aginary sketch of a volcanic vent on the moon in the days when the craters were active. The eruption is here in the full flush of its energy, when the internal forces are hurling forth a fountain of ashes or stones, which fall at a considerable distance from the vent ; and these accumulations constitute the rampart surround- ing the crater. The second cut depicts the crater in a later stage of its history. The prodigious explosive power has now been exhausted, and perhaps has been intermitted for some time. A feeble jet issues from the vent, and deposits the materials close around the orifice, and thus gradually raises a mountain in the center.
Besides the craters and their surrounding barriers, there are ranges of mountains on the moon, and flat plains which were once named "seas," before it was found that water did not exist there. Astronomers also see bright ridges, or lines, or cracks of light, hard to explain.
One of the chief craters is called " Ptolemy," and in size it is roughly calculated to be no less than one hundred and fourteen miles across. Another, "Co- pernicus," is about fifty-six miles; and another, "Tycho," about fifty-four miles. The central cone- mountain of Tycho is five thousand feet high. The crater of "Schickard" is supposed to be as much as one hundred and thirty-three miles in diameter.
Astronomers have agreed to name these craters after the great discoverers who enlarged our knowl^ edge of the solar and sidereal systems. It is fitting that these great names are suggested every time the moon is seen through a telescope. To Ptolemy we
YET MORE ABOUT THE MOON. 1 75
are indebted for what is known as "The Ptolemaic System of the Universe," which makes the earth the center aronnd which the snn, moon, planets, and stars all revolve, and explains the apparently erratic move- ments of the planets by supposing their orbits to be epicycles; that is, curves returning upon themselves and forming loops. Tycho Brahe was willing to allow, with Copernicus, that the planets all revolved around the sun; but he taught that both sun and planets turned around the earth.
The system known as "The Copernican,, is now known to be the only true one, and it is universally accepted. It is so called after Nicolaus Copernicus, who was born in Thorn, Prussia, February 19, 1473. He was educated for the Church, and studied medi- cine, but devoted himself especially to astronomy.
Without being precisely a great genius, this quiet and thoughtful monk seems to have been wise far beyond the age in which he lived, and remarkable for his independence of mind. He had a "profound sagacity," and a wide general grasp of scientific subjects.
The extremely complicated and cumbrous nature of the Ptolemaic system appeared to his judgment hardly compatible with the harmony and simplicity elsewhere characteristic of nature. Moreover, he was impressed and perplexed by the very marked changes in the brilliancy of the planets at different seasons. These changes now are no difficulty at all. Venus, Mars, Jupiter, when on the same side of the sun as ourselves, are comparatively near to us, and naturally look much more bright in consequence of that near-
176 STORY OF THE SUN, MOON, AND STARS.
ness than when they are on the opposite side of the sun from ourselves. But under the Ptolemaic system, each planet was supposed to revolve round our earth, and to be always at about the same distance from us; therefore, why such variations in their brilliancy?
NICOI^AUS COPERNICUS.
During thirty-six long years he patiently worked out this theory, and during part of those thirty-six years he wrote the one great book of his lifetime, ex- plaining the newer view of the Solar System which
YET MORE ABOUT THE MOON. 1 77
had taken hold of his reason and imagination. This book, named De Revolutionibus Orbium Ccelestium, or, " Concerning the Revolutions of the Celestial Spheres," which came out only a few hours before his death, was dedicated to the Bishop of Rome — a little touch of worldly wisdom which doubtless staved off for a while the opposition of the Vatican.
Copernicus was not the first who thought of in- terpreting the celestial motions by the theory of the earth's motion. That immortal astronomer has taken care to give, with rare sincerity, the passages in the ancient writers from which he derived the first idea of the probability of this motion — especially Cicero, who attributed this opinion to Nicetas of Syracuse; Plu- tarch, who puts forward the names of Philolaus, He- raclides of Pontus, and Ecphantus the Pythagorean; Martianus Capella, who adopted, with the Egyptians, the motion of Mercury and Venus around the sun, etc. Even a hundred years before the publication of the work of Copernicus, Cardinal Nicolas of Cusa, in 1444, in his great theological and scientific encyclopedia, had also spoken in favor of the idea of the earth's motion and the plurality of worlds. From ancient times to the age of Copernicus, the system of the earth's immobility had been doubted by clear-sighted minds, and that of the earth's motion was proposed under different forms. But all these attempts still leave to Copernicus the glory of establishing it defi- nitely.
Not content with merely admitting the idea of the earth's motion as a simple arbitrary hypothesis, which Several astronomers had done before him, he wished —
178 story o^ The: Sun, moon, and stars.
and this is his glory — to demonstrate it to himself by- acquiring the conviction by study, and wrote his book to prove it. The true prophet of a creed, the apostle of a doctrine, the author of a theory, is the man who, by his works, demonstrates the theory, makes the creed believed in, and spreads the doctrine. He is not the creator. "There is nothing new under the sun," says an ancient proverb. We may rather say, Nothing which succeeds is entirely new. The new- born is unformed and incapable. The greatest things are born from a state of germ, so to say, and increase unperceived. Ideas fertilize each other. The sciences help each other; progress marches. Men often feel a truth, sympathize with an opinion, touch a discovery, without knowing it. The day arrives when a syn- thetical mind feels in some way an idea, almost ripe, becoming incarnate in his brain. He becomes enam- ored of it, he fondles it, he contemplates it. It grows as he regards it. He sees, grouping round it, a mul- titude of elements which help to support it. To him the idea becomes a doctrine. Then, like the apostles of good tidings, he becomes an evangelist, announces the truth, proves it by his works, and all recognize in him the author of the new contemplation of nature, although all know perfectly well that he has not in- vented the idea, and that many others before him have foreseen its grandeur.
Such is the position of Copernicus in the history of astronomy. The hypothesis of the earth's motion had been suggested long before his birth on this planet. This theory counted partisans in his time But he — he did his work. He examined it with the patience
YET MORE ABOUT THE MOON. 179
of an astronomer, the rigor of a mathematician, the sincerity of a sage, and the mind of a philosopher. He demonstrated it in his works. Then he died with- out seeing it understood, and it was not till a century after his death that astronomy adopted it, and popular- ized it by teaching it. However, Copernicus is really the author of the true system of the world, and his name will remain respected to the end of time.
The so-called " seas' ' on the moon are those large dark spots to be seen on its surface, in the shape of "eyes, nose, and mouth," or of the famous old man with his bundle of sticks. The brighter parts are the more mountainous parts.
The chief ranges of lunar mountains have been named by astronomers after mountains on earth, such as the Apennines, the Alps, the Caucasian range, the Carpathian and the Altai Mountains.
CHAPTER XVI.
MERCURY, VENUS, AND MARS.
Once again we have to journey through the high- roads of the Solar System, paying a brief visit to each in turn of our seven chief brother-and-sister planets, and learning a few more leading facts about them. Having gone the same way before, it will not now seem quite so far.
Busy, hurrying Mercury! we must meet him first in his wild rush through space. If he were to slacken speed for a single instant, he would begin to fall with fearful rapidity towards the sun. And if Mercury were to drop into one of those huge black chasms of rent furnace-flame on the sun's surface, there would be a speedy end to his life as a planet.
Mercury's day is about the same length as our day, and his year is about one quarter the length of our year. If Mercury has spring, summer, autumn, and winter, each season must be extremely short; but this depends upon whether Mercury's axis slopes like the earth's axis — a matter difficult to find out. Mercury is always so near to the sun, that it is by no means easy to observe him well.
We know more about his orbit than his axis. The earth's orbit, as before explained, is not a circle, but an ellipse or oval. Mercury's orbit is an ellipse also, and a much longer — or, as it is called, a more eccen- tric— ellipse. The earth is three millions of miles
t8o
MERCURY, VENUS, AND MARS. l8l
nearer to the sun at one time of the year, than six months before or after. Mercury is no less than fif- teen millons of miles nearer at one time than another, which must make a marked difference in the amount of heat received.
Even when the distance is greatest, the sun as seen from Mercury looks four and a half times as large as the sun we see. What a blazing splendor of light! It is not easy to imagine human beings living there, in such heat and glare, and with either no changes of season at all, or such very short seasons rapidly fol- lowing one another. Mercury may, and very likely does, abound with living creatures, as much as the earth abounds with them ; only one fancies they must be altogether a different kind of living creatures from any ever seen on earth. And yet we do not know. Man can so wonderfully adapt himself or be adapted to dif- ferent climates on earth, from extreme heat to extreme cold, that we can not tell how far this adapting power may reach.
Both Mercury and Venus seem to be enfolded in dense, cloud-laden atmospheres, rarely parting so as to allow us to get even a glimpse of the real planets within the thick, light-reflecting covering. Some have thought that a heavy, moist, protecting atmos- phere may help to ward off the intense heat, and to make Mercury a more habitable place. Our earthly atmosphere is rather of a kind to store up heat, and to make us warmer than we should be without it; but there might be vapors differently constituted which might act in some other way. At all events, we know how easily God can have adapted either the planet
l82 STORY OF THE SUN, MOON, AND STARS.
to the creatures he meant to place there, or the crea- tures to the climate. "All things are possible" to him. The how and the what are interesting questions for us, but we must often be content to wait for an answer.
A thick, gray ring or belt has been noticed round the small, black disk of Mercury, while it has passed between us and the sun. The edge of Mercury, seen against the bright photosphere beyond, would, if there were no atmosphere, be sharp and clear as the edge of the airless moon. This surrounding haze seems to show that Mercury has an atmosphere. The sunlight reflected from Mercury's envelope of clouds shines at least as brightly as if it were reflected from his solid body.
The small size of Mercury makes attraction on his surface much less than on earth. A lump of iron weighing on earth one pound, would weigh on Mer- cury only about seven ounces, or less than half as much. So a man would be a very light leaper indeed there, and an elephant might be quite a frolicsome animal. If there are star-gazers in Mercury, and if the cloud-laden atmosphere allows many clear views of the sky, the earth and Venus must both be beau- tiful to look upon. Each of the two would shine far more brightly than Jupiter, as seen at his best from earth.
Like Mercury, Venus, the next planet, has an orbit lying inside our orbit. Mercury and Venus are al- ways nearer to the sun than we are ; and if Mercury and Venus traveled round the sun in orbits, the planes of which were exactly the same as the plane of the
MERCURY, VENUS, AND MARS. 183
earth's orbit, we should very often see them creeping over the surface of the sun. Not that they really " creep over " it ; only, as they journey between the sun and us, we can see them pass like little black dots across the sun's disk. This is the same thing as when the moon passes across the sun's disk and eclipses it. But Mercury and Venus are too far away from us to cause any eclipse of the sun's light.
Mercury has given more trouble to astronomers than any other member of the system; for, owing to his proximity to the sun, he is usually lost in the solar glory, and is never seen in a dark part of the heavens, even at the time of his greatest distance. This circumstance, together with a small mass and an immense velocity, renders it difficult to catch and watch him. In high latitudes, where the twilight is strong and lengthened, while mists often overhang the hori- zon, the planet can seldom be seen with the naked eye. Hence an old astro-meteorologist contemptuously de- scribes him as "a squirting lacquey of the sun, who seldom shows his head in these parts, as if he was in debt." Copernicus lamented that he had never been able to obtain a sight of Mercury ; and the French as- tronomer Delambre saw him not more than twice with the naked eye.
The most favorable times for making observations are about an hour and three-quarters before sunrise in autumn, and after sunset in spring; but very clear weather and a good eye are required. At certain pe- riods, when between the earth and the sun, on a line joining the centers of the two bodies, Mercury ap- pears projected on the solar disk as a small, round, dark
184 STORY OF THE SUN, MOON, AND STARS.
spot. This is called a transit, and would occur during every revolution if the plane of his orbit coincided with that of the orbit of the earth. But as one-half of his orbit is a little above that of the earth, and the other half a little below it, he passes above or below the sun to the terrestial spectator, except at those in- tervals, when, being between us and the sun, he is also at one of the two opposite points where the planes of the respective orbits intersect each other. Then, stripped of all luster, the planet passes over the face of the great luminary as a black circular speck, af- fording evidence of his shining by reflected light, and of his spherical form.
The first transit of Mercury recorded in history was predicted by Kepler, and witnessed by Gassendi, at Paris, on the morning of a cloudy day, the 7th of November, 1631. It was toward nine o'clock when he saw the planet; but owing to its extreme smallness, he was at first inclined to think it was a minute solar spot. It was then going off the sun; and made its final egress toward half-past ten. The observed time of the transit was nearly five hours in advance of the computed time. This was a very satisfactory accord- ance for that age between theory and observation ; but it was the effect of a fortuitous combination of circum- stances, rather than of computations founded upon well-established data. " The crafty god," wrote Gas- sendi, in the peculiar style of his day, "had sought to deceive astronomers by passing over the sun a little earlier than was expected, and had drawn a veil of dark clouds over the earth in order to make his escape more effectual. But Apollo, knowing his knavish
i85
tricks from his infancy, would not allow him to pass altogether unnoticed. To be brief, I have been more fortunate than those hunters after Mercury who have sought the cunning god in the sun. I found him out, and saw him where no one else had hitherto seen him." Since Gassendi's time a number of transits have been observed.
These crossings of the sun's face, or " transits," as they are called, have been important matters. The transit of Venus especially was once eagerly looked for by astronomers, since, by close observations of Ve- nus's movements and positions, the distance of the sun could at that time be better calculated than in any other way. Other methods are now coming into vogue.
The transits of Venus are rare. Two come near together, separated by only eight years, and then for more than one hundred years the little dark body of Venus is never seen from earth to glide over the sun's photosphere. There was a transit of Venus in the year 1761, and another in the year 1769. There was a transit of Venus in 1874, and another in 1882. At the last transits it was found that the sun, instead of being ninety-five millions of miles away, as astrono- mers thought, was only ninety- three millions of miles away. The reason why these transits happen so seldom, is that the orbits of Mercury and Venus lie in rather a different plane or level from the earth's orbit. So, like the moon, though often passing between us and the sun, they generally go just a little higher or just a little lower than his bright face.
Mercury and Venus show phases like the moon, al- though they do not circle round the earth as the moon
l86 STORY OF THK SUN, MOON, AND STARS.
does. These " phases," or changes of shape, are prob- ably never visible except through a telescope. It will be easier to think about the phases of Venus alone, than to consider both together. Her orbit lies within the earth's orbit, and the earth and Venus travel round the sun — as do all the planets — in the same direction. But as Venus' s pathway is shorter than ours, and as her speed is greater, she is much the quickest about her yearly journey, and she overtakes us again and again at different points of our orbit in turn.
At one time she comes be- tween us and the sun. That is her nearest position to us, and she is then only about twenty-five mill-
PHASES OF VENVS. iotlS of DlileS dis-
tant. A beautiful sight she would be, but unfortu- nately her bright side is entirely turned away, and only her dark side is turned towards us. So then she is "new Venus," and is invisible.
At another time she is completely beyond the sun, and at her farthest position away from us. Her shin- ing is quite lost in the sun's rays coming between. And though we get a good view of her as " full Ve- nus," at a little to one side or the other, yet so great is her distance — as much as one hundred and fifty- seven millions of miles — that her size and brightness are very much lessened.
MERCURY, VENUS, AND MARS. 1 87
Between these two nearest and farthest points, she occupies two middle distances, one on each side of the sun. Then, like the moon at her " quarters," she turns to us only half of her bright side. But this is the best view of Venus that we have, as a brilliant, untwinkling, starlike form, — the Evening Star of an- cients and of poets. Between these four leading posi- tions Venus is always traveling gradually from one to another — always either waxing or waning in size and in brightness. Mercury passes through the same seeming changes.
Inhabitants of Venus must have a glorious view of the earth, with her attendant moon. For just at the time when the two planets are nearest together, and when she is only "new Venus" to us, a dark and in- visible body, the earth is " full earth " to Venus. The very best sight we ever have of Venus can not come near that sight. But if Mercury and Venus really are so often covered with heavy clouds as astronomers be- lieve, this must greatly interfere with any habits of star-gazing.
Venus and the earth have often been called twin- sister planets. There are many points of likeness be- tween them. In size they differ little, and in length of day they are within an hour of being the same. Earth certainly has a companion-moon, and Venus, it is believed, has not. At one time several astronomers were pretty certain that they had caught glimpses of a moon ; but the supposed moon has of late quite van- ished, and nobody can say whether it ever really ex- isted. Venus travels in an ellipse which comes nearer to being a circle than the orbit of any other planet.
1 88 STORY OF THK SUN, MOON, AND STARS.
Mountain-shadows have been watched through the telescope, in Venus, as in the moon. Some astrono- mers have believed that they saw signs of very lofty mountains — as much as twenty-eight miles, or four times the height of our highest earthly mountains, but this requires confirmation.
There is a good deal of uncertainty about the climate of Venus. The heat there must greatly sur- pass heat ever felt on earth — the sun being about double the apparent size of our sun, and pouring out nearly double the amount of light and heat that we receive.
This difference may be met, as already stated, by a sheltering, cloudy atmosphere, or the inhabitants may have frames and eyesight suited to the increased glare and warmth.
An atmosphere and water exist there as here. From what we have seen above of the rapid and vio- lent seasons of this planet, we might think that the agitations of the winds, the rains, and the storms would surpass everything which we see and experi- ence here, and that its atmosphere and its seas would be subject to a continual evaporation and precipitation in torrential rains — an hypothesis confirmed by its light, due, doubtless, to reflection from its upper clouds, and to the multiplicity of the clouds them- selves. To judge by our own impressions, we should be much less pleased with this country than with our own, and it is even very probable that our physical organization, accommodating and complaisant as it is, could not become acclimatized to such variations of temperature. But it is not necessary to conclude from
MERCURY, VENUS, AND MARS. 189
this that Venus is uninhabitable and uninhabited. We may even suppose, without exaggeration, that its inhabitants, organized to live in the midst of these conditions, find themselves at their ease, like a fish in water, and think that our earth is too monotonous and too cold to serve as an abode for active and intelligent beings.
Of what nature are the inhabitants of Venus? Do they resemble us in physical form? Are they endowed with an intelligence analogous to ours? Do they pass their life in pleasure, as Bernardin de St. Pierre said ; or, rather, are they so tormented by the inclemency of their seasons that they have no delicate perception, and are incapable of any scientific or artistic atten- tion? These are interesting questions, to which we have no reply. All that we can say is, that organized life on Venus must be little different from terrestrial life, and that this world is one of those which resemble ours most. It should, then, be inhabited by vegetable, animal, and human races but little different from those which people our planet. As to imagining it desert or sterile — this is an hypothesis which could not arise in the brain of any naturalist. The action of the di- vine sun must be there, as in Mercury, still more fer- tile than his terrestrial work, already so wonderful. We may add that Venus and Mercury, having been formed after the earth, are relatively younger than our planet.
It is believed also that the axis of Venus, instead of being slanted only as much as the earth's axis, is tilted much more. Even if the tilting is less than some have supposed, it is probably very considerable.
190 STORY OF THE SUN, MOON, AND STARS.
If Venus really does "lie over" in such a manner, certain startling changes of climate on its surface — unpleasant changes, according to our ideas — would take place.
Like earth, Venus would have her two arctic re- gions, where a burning summer's day would succeed a bitter winter's night, each half a year in length. She would have also her tropical region — only in that region intense cold would alternate with intense heat, brief seasons of each in turn. And between the trop- ics and the arctic regions would lie wide belts, by turns entirely tropical and entirely arctic. The rapidity and severity of these changes, following one another in a year about as long as eight of our months, would seem to be too much for any human frame to endure. But it all rests upon an if And we may be quite sure that if there are any manner of human beings in Venus, their frames are well suited to the climate of their world.
Though Mars is one of the inner group of four small planets, divided by the zone of asteroids from the outer group of four great planets, yet he belongs to the outside set of Superior Planets. His orbit sur- rounds ours, being at all points farther off from the sun. Very slight "phases" have been seen in Mars. He turns to us, from time to time, just enough of his dark side to prove that he has a dark side, and that he does not shine like a star by his own light. But the phases on that planet are by no means marked as they are with Venus.
Until lately it was believed that Mars possessed no moons. Two very small ones have, however, been
MERCURY, VENUS, AND MARS. 19I
lately found circling round him.* They have been named Deimos and Phobos, after the "sons of Mars" in Greek mythology. Deimos travels round Mars in thirty-nine hours, while Phobos performs the same journey in the astonishingly short period of seven hours and a half!
We have here, then, a system very different from that of the earth and moon. But the most curious point is the rapidity with which the inner satellite of
MARS AND THE PATH OF ITS SATEUJTES.
Mars revolves round its planet. This revolution is performed in seven hours, thirty-nine minutes, fifteen seconds, although the world of Mars rotates on itself in twenty-four hours, thirty-seven minutes — that is to
* The discovery of the two moons is due to the agency of a woman. Professor Asaph Hall, of Washington City, was searching by the aid of the most powerful telescope which had yet been di- rected to Mars, and at the very moment when the planet was in the most favorable condition for observation. Having searched in vain during several evenings in August, 1877, he was ahout to give up, when Mrs. Hall begged him to search a little more. He did so, and on the night of the nth he discovered the first of the satellites, and then on the 17th the second.
1 92 STORY OF THE SUN, MOON, AND STARS.
say, this moon turns much more quickly than the planet itself. This fact is inconsistent with all the ideas we have had up to the present on the law of formation of the celestial bodies. Thus, while the sun appears to revolve in the Martian sky in a slow journey of more than twenty-four hours, the inner moon performs its entire revolution in a third of a day. It follows that it rises in the west and it sets in the east! It passes the second moon, eclipses it from time to time, and goes through all its phases in eleven hours, each quarter not lasting even three hours. What a singular world!
These satellites are quite small — they are the smallest celestial bodies we know. The brightness of the planet prevents us from measuring them ex- actly. It seems, however, that the nearer is the larger, and shows the brightness of a star of the tenth magnitude, and that the second shines as a star of the twelfth magnitude. According to the most trust- worthy photometric measures, the first satellite may have a diameter of 7.45 miles, and the second a diameter of 6.2 miles. The larger of these two worlds is scarcely larger than Paris. Should we honor them with the title of worlds? They are not even terrestrial continents, nor empires, nor kingdoms, nor provinces, nor departments. Alexander, Caesar, Charlemagne, or Napoleon, might care but little to receive the scepter of such worlds. Gulliver might juggle with them. Who knows, however? The vanity ot men being generally in the direct ratio of their mediocrity, the microscopical reasoning mites which doubtless swarm on their surface have also, perhaps,
MERCURY, VENUS, AND MARS. 193
permanent armies, which mutilate each other for the possession of a grain of sand.
These two little moons received from their dis- coverer the names of Deimos (Terror) and P hobos (Flight), suggested by the two verses of Homer's ' ' Iliad' ' which represent Mars descending on the earth to avenge the death of his son Ascalaphus :
"He ordered Terror and Flight to yoke his steeds, And he himself put on his glittering arms."
Phobos is the name of the nearer satellite ; Deimos, that of the more distant.
The existence of these little globes had already been suspected from analogy, and thinkers had fre- quently suggested that, since the earth has one satel- lite, Mars should have two, Jupiter four, Saturn eight ; and this is indeed the fact — though as Jupiter is now found to have Jive satellites, this arithmetical progres- sion is upset. But as we experience too often in practice the insufficiency of these reasonings of purely human logic, we can not give them more value than they really possess. We might suppose in the same way now that Uranus has sixteen satellites, and Nep- tune thirty-two. This is possible ; but we know noth- ing of them, and have not even the right to consider this proportion as probable. It is not the less curious to read the following passage, written by Voltaire in 1750 in his masterpiece, the "Micromegas:"
" On leaving Jupiter, our travelers crossed a space
of about a hundred millions of leagues, and reached
the planet Mars. They saw two moons, which wait on
this planet, and which have escaped the gaze of as-
13
194 STORY OF THE SUN, MOON, AND STARS.
tronomers. I know well that Father Castel wrote against the existence of these two moons ; but I agree with those who reason from analogy. These good philosophers know how difficult it would be for Mars, which is so far from the sun, to get on with less than two moons. However this may be, our people found it so small that they feared they might not find any- thing to lie upon, and went on their way."
Here we have unquestionably a very clear proph- ecy, a rare quality in this kind of writing. The astro- nomico-philosophical romance of "Micromegas" has been considered as an imitation of Gulliver. L,et us open the masterpiece of Swift himself, composed about 1720, and we read, word for word, in Chapter III of the "Voyage to L,aputa:"
" Certain astronomers . . . spend the greatest part of their lives in observing the celestial bodies, which they do by the assistance of glasses far excel- ling ours in goodness. For this advantage hath en- abled them to extend the discoveries much farther than our astronomers in Europe ; for they have made a catalogue of ten thousand fixed stars, whereas the largest of ours do not contain above one-third part of that number. They have likewise discovered two lesser stars, or satellites, which revolve about Mars, whereof the innermost is distant from the center of the primary planet exactly three of his diameters, and the outermost five. The former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near in the same proportion with the cubes of their distance from the center of Mars, which evidently
MERCURY, VENUS, AND MARS. 1 95
shows them to be governed by the same law of gravi- tation that influences the other heavenly bodies."
What are we to think of this double prediction of the two satellites of Mars? Indeed, the prophecies which have been made so much of in certain doc- trinal arguments have not always been as clear, nor the coincidences so striking. However, it is evident that no one had ever seen these satellites before 1877, and that there was in this hit merely the capricious work of chance. We may even remark that both the English and French authors have only spoken ironically against the mathematicians, and that in 1610, Kepler, on receiving the news of the discovery of the satel- lites of Jupiter, wrote to his friend Wachenfals that "not only the existence of these satellites appeared to him probable, but that doubtless there might yet be found two to Mars, six or eight to Saturn, and perhaps one to Venus and Mercury." We can not, assuredly, help noticing that reasoning from analogy is here found on the right road. However this may be, this discovery truly constitutes one of the most interesting facts of contemporary astronomy.
Mars is not only much smaller than th<* earth, but a good deal less dense in his "make." His material is only about three-quarters as heavy as an equal amount of the earth's material. A very heavy man on earth would be a most light and active individual on Mars. Gold taken from earth to Mars would weigh there no more than tin weighs upon earth.
Mars has, it seems, an atmosphere, even as earth has. Of all the planets Mars, is the only one whose actual surface is discernible in the telescope. Mer-
196 STORY OF THE SUN, MOON, AND STARS.
cury and Venus are so hidden by dense envelopes of clouds that the real planets within are only now and then to be dimly caught sight of. Jupiter and Saturn are so completely enwrapped in mighty masses of vapor, that we can not even be certain whether there are any solid bodies at all inside.
But Mars can be studied. Here and there, it is true, clouds sweep over the landscape, hiding from view for a little while one continent or another, one sea or another, growing, changing, melting away, as do the clouds of earth. Still, though these clouds come and go, there are other markings on the surface of Mars which do not change. Or, rather, they only change so much as the continents and oceans of earth would seem to vary, if watched from another planet, as the daily movement of earth carried them from west to east, or as they might be hidden for a while by cloud-layers coming between. It has been curi- ously noted that these clouds over Mars form often in the morning and evening, and are afterwards dis- persed by the heat of midday. Also there seems every reason to believe that rainfalls take place in Mars as upon earth.
The red color of Mars is well known. This does not vanish in the telescope, but it is found that parts only have the red or orange hue, while other parts are dark and greenish. These are the markings which remain always the same, and they have been so closely examined that more is known about the geog- raphy of Mars than of any other world outside our own.
Mars, at his nearest point, does not draw closer to
MERCURY, VENUS, AND MARS. I97
us than forty millions of miles. At such a distance one must not speak too confidently. There are, how- ever, many reasons for believing that the red portions are continents and that the green portions are oceans.
The spectroscope has lately shown us that water does really exist in the atmosphere of Mars — unlike the dreary, waterless moon. So we no longer doubt that the cloudlike appearances are clouds, and that rain sometimes falls on Mars. If there is rain, and if there are clouds and vapor, there are probably oceans also.
Two singular white spots are to be seen at the north and south poles, which we believe to be polar ice and snow. Somebody looking at our earth in like manner from a distance, would doubtless perceive two such white snow-spots. These two polar caps are seen to vary with the seasons. When the north pole of Mars is turned towards the sun, the white spot there grows smaller ; and at the same time, the south pole of Mars being turned away from the sun, the white spot there grows larger. Again, when the south pole is towards the sun, and the north pole away from the sun, the white spot at the south is seen to be the smallest, and the white spot at the north is seen to be the largest. This is exactly what takes place in the summers and winters of our north and south poles.
The markings of Mars have been so carefully stud- ied, that at last a map has been made of the planet — a map of a world, never less than forty millions of miles away! Names have been given to the conti- nents and oceans — such as Dawes Continent, Herschel Continent, De La Rue Ocean, Airy Sea, Huggins Inlet, and so on.
I98 STORY OF THE SUN, MOON, AND STARS.
Land and water seem to be very differently ar- ranged on Mars from what they are on earth. Here we have about three times as much water as land, and to get from one continent to another without crossing the sea is in some cases impossible. But a traveler there might go most conveniently to and fro, hither and thither, to all parts of his world, either on land or on water, without any change. If he preferred water, he would never need to set foot on land; and if he preferred land, he would never need to enter a boat. The two are so curiously mingled together, narrow necks of land running side by side with long, narrow sea-inlets, that Atlantic and Pacific Oceans are un- known.
Some have wondered whether the reddish color of the land may be caused by grass and trees being red instead of green. Very strange if so it were. But in that case, no doubt the inhabitants of Mars would find green just as trying to their eyesight, as we should find red trying to ours.
CHAPTER XVII.
JUPITER.
Passing at one leap over the belt of tiny asteroids, about which we know little beyond their general move- ment, and the size and weight of a few among them, we reach at once the giant planet Jupiter: Mighty Jupiter, hurrying ever onward, with a speed, not indeed equal to that of Mercury or of our earth, yet eighty times as rapid as the speed of a cannon-ball ! Think of a huge body, equal in bulk to twelve hundred earths, equal in weight to three hundred earths, rush- ing ceaselessly through space, at the rate of seven hundred thousand miles a day!
Jupiter's shape is greatly flattened at the poles. He spins rapidly on his axis, once in nearly ten hours, and has therefore a five hours' day and a five hours* night. As the slope of his axis is exceedingly slight, he can boast little or no changes of season. The cli- mate near the poles has never much of the sun's heat. In fact, all the year round the sun must shine upon Jupiter much as he shines on the earth at the equi- noxes.
But the amount of light and heat received by Ju- piter from the sun is only about one twenty-fifth part of that which we receive on earth; and the sun, as seen from Jupiter, can have but a small, round surface, not even one-quarter the diameter of the sun we see in the sky.
199
200 STORY OK THE SUN, MOON, AND STARS.
When looked at with magnifying power, the bright, starlike Jupiter grows into a broad, softly-shining disk or plate, with flattened top and bottom, and five tiny, bright moons close at hand. Sometimes one moon is on one side, and four are on the other; sometimes
GENERAL ASPECT OF JUPITER— SATELLITE AND ITS SHADOW.
two are one side and three on the other; sometimes one or more are either hidden behind Jupiter or pass- ing in front of him. Jupiter has also curious mark- ings on his surface, visible through a telescope. These markings often undergo changes; for Jupiter is no chill, fixed, dead world, such as the moon seems to be. There are dark belts and bright belts, usually run- ning in a line with the equator, from east to west.
JUPITER. 20I
Across the regions of the equator lies commonly a band of pearly white, with a dark band on either side of " coppery, ruddy, or even purplish" hue. Light and dark belts follow one after another, up to the north pole and down to the south pole.
When we talk of " north and south poles" in the other planets, we merely mean those poles which point towards those portions of the starry heavens which we have chosen to call " northern " and "south- ern." You know that all the chief planets travel round the sun in very nearly the same plane or flat surface that we do ourselves. That plane is called the "plane of the ecliptic." Suppose that you had an enormous sheet of cardboard, and that in the middle of this cardboard the sun were fixed, half his body being above and half below. At a little distance, fixed in like manner in the card, would be the small body of the earth, half above and half below, her axis being in a slanting position. The piece of cardboard repre- sents what is called in the heavens the plane of the ecliptic — an imaginary flat surface, cutting exactly through the middle of the sun and of the earth.
If the planets all traveled in the same precise plane, they would all be fixed in the cardboard just like the earth, half the body of each above and half below. As they do not so travel, some would have to be placed a little higher, some a little lower, according to what part of their orbits they were on. This supposed cardboard "plane of the ecliptic" would divide the heavens into two halves. One half, containing the constellations of the Great Bear, the Little Bear, Ce- pheus, Draco, and others, would be called the Northern
203 STORY OF THE SUN, MOON, AND STARS.
Heavens. One end of the earth's axis, pointing just now nearly to the Polar Star, we name the North Pole; and all poles of planets pointing towards this northern half of the heavens, are in like manner named by us their north poles.
With regard to west and east, lay in imagination upon this cardboard plane a watch, with its face up- wards ; remembering that all the planets and nearly all the moons of the Solar System are said both to spin on their axes, and to travel in their orbits round the sun, from west to east. Note how the hands of your watch would move in such a position. The "west to east" motions of planets and moons would be in exactly the opposite direction from what the mo- tions of the watch-hands would be. ) (To return to Jupiter. It is believed that these bands of color are owing to a heavy, dense atmos- phere, loaded with vast masses of cloudy vapor. By the " size " of Jupiter, we really mean the size of this outside envelope of clouds. ^How large the solid body within may be, or whether there is any such solid body at all, we do not know?) The extreme lightness of Jupiter, as compared with his great size, has caused strong doubts on this headA
The white belts are supposed to be the outer side of cloud-masses shining in the sunlight. Travelers in the Alps have seen such cloud-masses, spreading over the whole country beneath their feet, white as driven snow, and shining in the sunbeams which they were hiding from villages below ; or looking like soft masses of cotton- wool, from which the mountain- peaks rose sharply here and there.
JUPITER. 203
The dark spaces between seem to be rifts or breaks in the clouds. Whether, when we look at those dark spaces, we are looking at the body of Jupiter, or only at lower layers of clouds, is not known. But some- times blacker spots show upon the dark cloud-belts, and this seems rather as if they were only lower lay- ers of clouds, the black spots giving us peeps down into still lower and deeper layers, or else perhaps to the planet itself. These appearances remind one strongly of the sun-spots, each with its penumbra, umbra, and nucleus. Occasionally bright white spots show, instead of dark ones. It is thought that they may be caused by a violent upward rush of dense clouds of white vapor. The white spots again recall the sun and hisfaculcz.
Jupiter's bands are not fixed. Great changes go on constantly among them. Sometimes a white band will turn dark-colored, or a dark band will turn white. Sometimes few and sometimes many belts are to be seen. Sometimes a dark belt will lie slanting across the others, nearly from north to south. Once, in a single hour, an entirely new belt was seen to come into shape. Another time, two whole belts vanished in one day. The bands, in which such rapid move- ments are seen, are often thousands of miles in breadth. Sometimes these wide zones of clouds will remain for weeks the same. At another time a break or rift in them will be seen to journey swiftly over the surface of the planet.
The winds on earth are often destructive. A hur- ricane, moving at the rate of ninety miles an hour, will carry away whole buildings and level entire plan-
204 STORY OF THE SUN, MOON, AND STARS.
tations. Such hurricanes rarely, if ever, last more than a few hours. But winds in Jupiter, judging from the movements of the clouds, often travel at the rate of one hundred and fifty miles an hour; and that, not for hours only, but for many weeks together. What manner of living beings could stand such weather may well be questioned. ^^ (Another difficulty which arises is as to the cause of these tremendous disturbances on Jupiter. Our earthly storms are brought about by the heat of the sun acting on our atmosphere. But the sun-heat which reaches Jupiter seems very far from enough to raise such vast clouds of vapor, and to bring about such prolonged and tremendous hurricanes of wind.
What if there is another cause ? What if Jupiter is not a cooled body like our earth, but a liquid, seeth- ing, bubbling mass of fiery heat — -just as we believe our earth was once upon a time, in long past ages, be- fore her outside crust became cold enough for men and animals to live thereon? The7i, indeed, we could un- derstand how, instead of oceans lying on his surface, all the water of Jupiter would be driven aloft to hang in masses of steam or be condensed into vast cloud- layers. Then we could understand why a perpetual stir of rushing winds should disturb the planet's at- mosphere.
In that case would Jupiter be a planet at all ? Cer- tainly— in the sense of obeying the sun's control. Our earth was once, we believe, a globe of melted matter, glowing with heat — and farther back still, possibly, a globe of gas. Some people are very positive about these past changes ; but it is wise not to be over-
JUPITER. 205
positive where we can not know to a certainty what has taken place. ' However, Jupiter may have cooled down only to the liquid state, and if he goes on cooling he may, by and by, gain a solid crust like the earth."")
This idea about Jupiter's hot and molten state be- longs quite to late years. Certain other matters seem to bear it out, though of actual proof we have none. It is thought, for instance, that the dull, coppery red light, showing often in the dark bands, may be a red glow from the heated body within. Also it has been calculated that Jupiter gives out much more light than our earth would do, if increased to his size and moved to his place — more, in fact, than we could reasonably expect him to give out. If so, whence does he obtain the extra brightness? If he does not shine by re- flected light alone, he probably shines also in some additional degree by his own light?}
But what about Jupiter being inhabited ? Would it in such a case be quite impossible? " Impossible " is not a word for us to use about matters where we are ignorant. We can only say that it is impossible for us to imagine any kind of living creatures finding a home there, if our present notions about the present state of Jupiter are correct. Then is the chief planet of the Solar System a huge, useless monument of God's power to create? Not so fast. Even as merely such a monument, he could not be useless. And even if he were put to no present use at all, it might be merely because this is a time of preparation for the future. God has his times of long and slow preparation, alike with worlds, with nations, and with individuals.
206 STORY OP THE SUN, MOON, AND STARS.
But now as to the five moons circling round Ju- piter. There used to be some very pretty ideas afloat about the wonderful beauty of the moons, as seen from Jupiter, their united brilliancy so far surpassing the shining of our one poor satellite, and making up for the dim light of Jupiter's sun.
A certain little difficulty was not quite enough con- sidered. If anybody were living on the surface of Ju- piter, he would have, one is inclined to think, small
SATEUJTES OF JUPITER COMPARED WITH THE EARTH AND MOON.
chance of often seeing the moons through the cloud- laden atmosphere.
The nearest of the tour larger moons to Jupiter would, it is true, appear — when visible at all — rather bigger than ours does to us; while the two next would be almost half as large, and the farthest about a quarter as large — supposing inhabitants of Jupiter to have our powers of vision.
All taken together they would cover a considerably larger space in the sky than does our moon. But it must be remembered that Jupiter's moons, like ours, shine merely by reflected sunlight. And so dim is the
JUPITER. 207
sunshine at that distance compared with what it is at our distance, that all the five moons together, even if full at the same time, could only give about one- sixteenth part of the light which we obtain from our one full moon.
Besides, they never are full together, seen from any one part of Jupiter. The four inner moons are never to be seen "full" at all ; for just when they might be so, they are eclipsed or shaded by Jupiter's shadow. The fourth sometimes escapes this eclipse, from being so much farther away.
A thought has been lately put forward, which may or may not have truth in it. What if — instead of Jupiter being a world, inhabited by animals and peo- ple, as is often supposed, with a small distant sun and five dim moons to give them light — what if Jupiter is himself in some sort a second sun to his moons, and what if those "moons" are really inhabited planets? It may be so. That is all we can say. The idea is not an impossible one.
The so-called "moims" are certainly small. But they are by no means too small for such a purpose. Jupiter would in that case, with his five moons circling round him, enjoying his light and warmth, be a small picture of the sun, with his four inner planets and the asteroids circling round him, basking in a more lavish amount of the same.
Picturing the moons as giving light to Jupiter, we find them seemingly dim and weak for such a pur- pose— though, of course, we may here make a grand mistake in supposing the eyesight of living creatures in Jupiter to be no better than our own eyesight.
2o8 STORY OF THE SUN, MOON, AND STARS.
Even upon earth a cat can see plainly where a man has to grope his way in darkness.
But by picturing the moons as inhabited, and Jupiter as giving out some measure of heat and light
THE SYSTEM OF JUPITER.
to make up for the lessened amount of light and heat received from the sun, the matter becomes more easy to our understanding.
The nearest moon has indeed a magnificent view of Jupiter as a huge bright disk in its sky, no less
JUPITER. 209
than three thousand times as large as our moon ap- pears to us, shining brightly with reflected sunlight, and it may be glowing with a red light of his own in addition. Even the farthest off of the five sees him with a face sixty-five times the size of our moon. And the varying colors and stormy changes in the cloud-belts, viewed thus near at hand, must afford marvelously beautiful effects.
Just as Mercury, Venus, Earth, and Mars travel round the sun, at different distances, nearly in the same plane, so Jupiter's five moons travel round him, at different distances, nearly in the same plane. Jupiter's moons are always to be seen in a line, not one high and another low, one near his pole and an- other near his equator.
The moon nearest to Jupiter, discovered in Sep- tember, 1892, by Professor Barnard, now of the Yerkes Observatory of the Chicago University, has a probable diameter of one hundred miles, and revolves round its primary in about twelve hours. The second satellite, named Io, is said to be over two thousand miles in diameter, travels round Jupiter in less than two of our days, and is eclipsed by Jupiter's shadow once in every forty-two hours.
The third moon, Europa, is rather smaller, takes over three days to its journey, and suffers eclipse once in every eighty-five hours.
The fourth moon, Ganymede, is believed to be con- siderably larger than Mercury, journeys round Jupiter once a week, and is eclipsed once every hundred and seventy-one hours.
The fifth moon, Callisto, is also said to be slightly 14
2IO STORY OF THE SUN, MOON, AND STARS.
larger than Mercury, performs its journey in some- thing more than sixteen days, and from its greater distance suffers eclipse less often than the other four.
The distance of the nearest is more than one hun- dred thousand miles from Jupiter ; that of the farthest, more than one million miles.
The following table presents more minutely the results of the latest discoveries concerning these sat- ellites :
SATELLITES.
DISTANCE FROM CENTER OF
JUPITER.
DIAMETER.
PERIOD OF
REVOLUTION.
1. Barnard's Satellite,
2. IO,
3. Europa,
4. Ganymede
5. Callisto,
112,500 miles. 266,000 " 424,000 " 676,000 " 1,189,000 "
100 miles. 2,356 " 2,046 « 3,596 "
2,728 «
D. H. M. S.
11 57 23
1 18 27 33
3 13 13 42
7 3 42 33
16 15 32 11
The fact of these eclipses, and of the shadow thrown by Jupiter's body, shows plainly that though he may give out some measure of light, as has been suggested, yet that light can not be strong, or it would prevent any shadow from being thrown by the sunlight. Also, the dense masses of cloud around him, though reflecting sunlight brightly, would shut in much of his own light. Possibly it is chiefly as heat-giver and as sunlight-reflector that Jupiter serves his five satellites.
As with our own moon, so with Jupiter's moons, the real center of their orbit is the sun, and not Jupiter. They accompany Jupiter in his journey, controlled by the sun, and immensely influenced by Jupiter.
JUPITER. 211
At night the spectacle of the sky seen from Ju- piter is, with reference to the constellations, the same as that which we see from the earth. There, as here, shine Orion, the Great Bear, Pegasus, Andromeda, Gemini, and all the other constellations, as well as the diamonds of our sky: Sirius, Vega, Capella, Procyon, Rigel, and their rivals. The 390,000,000 of miles which separate us from Jupiter in no way alter the celestial perspectives. But the most curious char- acter of this sky is unquestionably the spectacle of the five moons, each of which shows a different motion. The second moves in the firmament with an enor- mous velocity, and Barnard's satellite still faster, and produce almost every day total eclipses of the sun in the equatorial regions. The four inner moons are eclipsed at each revolution, just at the hours when they are at their "full." The fifth alone attains the full phase.
Contrary to the generally received opinion, these bodies do not give to Jupiter all the light which is supposed. We might think, in fact, as has been so often stated, that these five moons illuminate the nights five times better relatively than our single moon does in this respect, and that they supplement in some measure the feebleness of the light received from the sun. This result would be, assuredly, very agreeable, but nature has not so arranged it. The five satellites cover, it is true, an area of the sky greater than our moon, but they reflect the light of a sun twenty-seven times smaller than ours ; indeed, the total light reflected is only equal to a sixteenth of that of our full moon, even supposing the soil of these
212 STORY OF THE SUN, MOON, AND STARS.
satellites to be as white as it appears to be, especially the fifth satellite.
Jupiter appears to be a world still in process of formation, which lately — some thousands of centuries ago — served as a sun to his own system of five or perhaps more worlds. If the central body is not at present inhabited, his satellites may be. In this case, the magnificence of the spectacle presented by Jupiter himself to the inhabitants of the satellites is worthy of our attention. Seen from Barnard's satellite, Ju- piter's disk has a diameter of 470, or more than half the distance from the horizon to the zenith. Seen from the second satellite, the Jovian globe presents an immense disk of twenty degrees in diameter, or 1,400 times larger than the full moon! What a body! What a picture, with its belts, its cloud motions, and its glowing coloration, seen from so near! What a nocturnal sun ! — still warm, perhaps. Add to this the aspect of the satellites themselves seen from each other, and you have a spectacle of which no terrestrial night can give an idea.
Such is the world of Jupiter from the double point of view of its vital organization and of the spectacle of external nature, seen from this immense observa- tory.
The attraction of the planets has always played an important part in the motion of comets and the form of their orbits. The enormous size of Jupiter gives it more influence than any other planet, and we are not surprised that it should have seriously interfered with some of the comets that belong to the Solar System. We have already seen that Biela's comet
JUPITER.
213
was captured by Jupiter, and that it was probably dis- solved into meteoric dust. We show in the cut the orbits of eight others that circle around the sun, but retreat no farther away than Jupiter. These are the
ORBITS OF NINE COMETS CAPTURED BY JUPITER.
orbits as now determined, but they vary from age to age on account of disturbances of other planets. But it is not likely that the comets themselves will ever escape from the control of Jupiter.
CHAPTER XVIII.
SATURN.
The system of Jupiter is a simple system compared with that of Saturn, next in order. For whereas Jupiter has only five moons, Saturn has eight, and, in addition to these, he has three wonderful rings. Neither rings nor moons can be seen without a tele- scope, on account of Saturn's great distance from us — more than three thousand times the distance of the moon, or upwards of eight hundred millions of miles, Saturn's mean distance from the sun is eight hundred and seventy-six million seven hundred and sixty-seven thousand miles.
Saturn does not equal his mighty brother Jupiter in size, though he comes near enough in this respect to be called often his "twin" — just as that small pair of worlds, Venus and Earth, are called "twins." While Jupiter is equal in size to over one thousand two hundred earths, Saturn is equal to about seven hundred earths. And while Jupiter is equal in weight to three hundred earths, Saturn is only equal in weight to ninety earths. He appears to be made of very light materials — not more than three-quarters as dense as water. This would show the present state of Saturn to be very different from the present state of the earth. We are under the same uncertainty in speaking of Saturn as in speaking of Jupiter. Like Jupiter, Saturn is covered with dense masses of varying clouds, occa-
214
SATURN.
215
sionally opening and allowing the astronomer peeps into lower cloud-levels ; but rarely or never permitting the actual body of the planet to be seen.
The same perplexities also come in here, to be an- swered much in the same manner. We should cer- tainly expect that in a vast globe like Saturn the strong force of attraction would bind the whole into a
SATURN AND THE EARTH — COMPARATIVE SIZE.
dense solid mass; instead of which, Saturn is about the least solid of all the planets. He seems to be made up of a light, watery substance, surrounded by vapor.
One explanation can be offered. What if the globe of Saturn be still in a red-hot, molten state, keeping such water as would otherwise lie in oceans on his surface, floating aloft in masses of steam, the outer parts of which condense into clouds?
No one supposes that Jupiter and Saturn are in the same condition of fierce and tempestuous heat as the
2l6 STORY OF THB SUN, MOON, AND STARS.
sun. They may have been so once, but they must now have cooled down very many stages from that condition. Though no longer, however, a mass of far-reaching flames and fiery cyclones, the body of each may have only so far cooled as to have reached a stage of glowing molten red-heat, keeping all water in the form of vapor, and sending up strong rushes of burning air to cause the hurricanes which sweep to and fro the vast cloud-masses overhead.
And if this be the case, then, with Saturn as with Jupiter, comes the question, Can Saturn be inhabited? And if — though we may not say it is impossible, yet we feel it to be utterly unlikely — then again follows the question, What if Saturn's moons are inhabited?
Telescopic observations tempt us to believe that there is on this planet a quantity of heat greater than that which results from its distance from the sun; for the day-star as seen from Saturn is, as we have said, ninety times smaller in surface, and its heat and light are reduced in the same proportion. Water could only exist in the solid state of ice, and the vapor of water could not be produced so as to form clouds similar to ours. Now, meteorological variations are observed similar to those which we have noticed on Jupiter, but less intense. Facts, then, combine with theory to show us that the world of Saturn is at a temperature at least as high as ours, if not higher.
But the strangest feature of the Saturnian calendar is, unquestionably, its being complicated, not only with the fabulous number of 25,060 days in a year, but, further, with eight different kinds of months, of which the length varies from 22 hours to 79 days —
SATURN. 217
that is to say, from about two Saturnian days to 167. It is as if we had here eight moons revolving in eight different periods.
The inhabitants of such a world must assuredly differ strangely from us from all points of view. The specific lightness of the Saturnian substances and the density of the atmosphere will have con- ducted the vital organization in an extra-terrestrial direction, and the manifestations of life will be pro- duced and developed under unimaginable forms. To suppose that there is nothing fixed, that the planet it- self is but a skeleton, that the surface is liquid, that the living beings are gelatinous — in a word, that all is unstable — would be to surpass the limits of scientific induction.
The diameter of the largest moon is about half the diameter of the earth, or much larger than Mercury. The four inner satellites are all nearer to Saturn than our moon to us, though the most distant of the eight is ten times as far away. The inner moon takes less than twenty-three hours to travel round Saturn, and the outer one over seventy-nine days.
A great many charming descriptions have been worked up, with Saturn as with Jupiter, respecting the magnificent appearance of the eight radiant moons, joined to the glorious shining of the rings, as quite making up for the diminished light and heat of the sun. But here again comes in the doubt, whether really it is the moons who make up to Saturn for lack of light, or whether it is Saturn who makes up to the moons for lack of light.
Certainly, Saturn's cloudy covering would a little
2l8 STORY OF THE SUN, MOON, AND STARS.
interfere with observations of the moons by any in- habitants of the solid body within — supposing there be any solid body at all. And though it sounds very wonderful to have eight moons instead of one moon, yet all the eight together give Saturn only a very small part of the light which we receive from our one full moon — so much more dimly does the sun light them up at that enormous distance.
The same thing has been noticed with Saturn as with Jupiter — that he seems to shine more brightly than is to be expected in his position, from mere re- flection of the sun's rays. A glowing body within, sending a certain amount of added light through or between the masses of clouds, would explain av/ay this difficulty.
One more possible proof of Saturn's half-liquid state is to be found in his occasional very odd changes of shape. Astronomers have been startled by a pe- culiar bulging out on one side, taking off from his roundness, and giving a square-shouldered aspect. We may not say it is quite impossible that a solid globe should undergo such tremendous upheavals and outbursts as to raise a great portion of its surface five or six hundred miles above the usual level — the change being visible at a distance of eight hundred millions of miles. But it would be easier to under- stand the possibility of such an event, in the case of a liquid, seething mass, than in the case of a solid ball.
On the other hand this alteration of outline may be caused simply by a great upheaval not of the plan- et's surface, but of the overhanging layers of clouds.
SATURN. 219
Some such changes, only much slighter, have been remarked in Jupiter.
And now as to the rings. Nothing like them is to be seen elsewhere in the Solar System. They are be- lieved to be three in number; though some would divide them into more than three. Passing com- pletely round the whole body of Saturn, they rise, one beyond another, to a height of many thousands of miles.
The inner edge of the inner ring — an edge perhaps one hundred miles in thickness — is more than ten thousand miles from the surface of Saturn or more strictly speaking, from the outer surface of Sat- urn's cloudy envelope. A man standing exactly on the equator and looking up, even if no clouds came between, would scarcely be able to see such a slender dark line at such a height.
This dark, transparent ring, described sometimes as dusky, sometimes as richly purple, rises upwards to a height or breadth of nine thousand miles. Closely following it is a ring more brilliant than Saturn himself, over eighteen thousand miles in breadth. When as- tronomers talk of the "breadth " of these rings, it must be understood that they mean the width of the band measured upwards, in a direction away from the planet.
Beyond the broad, bright ring is a gap of about one thousand seven hundred miles. Then follows the third ring, ten thousand miles in breadth ; its outer- most edge being at a height of more than forty-eight thousand miles from Saturn. The color of the third ring is grayish, much like the gray markings often seen on Saturn.
220 STORY OF THE SUN, MOON, AND STARS.
What would not be our admiration, our astonish- ment, our stupor perhaps, if it were granted us to be transported there alive, and, among all these extra- terrestrial spectacles, to contemplate the strange as- pect of the rings, which stretch across the sky like a bridge suspended in the heights of the firmament! Suppose we lived on the Saturn ian equator itself, these rings would appear to us as a thin line drawn across the sky above our heads, and passing exactly through the zenith, rising from the east and increas- ing in width, then descending to the west and dimin- ishing according to perspective. Only there have we the rings precisely in the zenith. The traveler who journeys from the equator towards either pole leaves the plane of the rings, and these sink imperceptibly, at the same time that the two extremities cease to ap- pear diametrically opposite, and by degrees approach each other. What an amazing effect would be pro- duced by this gigantic arch, which springs from the horizon and spans the sky ! The celestial arch dimin- ishes in height as we approach the pole. When we reach the sixty-third degree of latitude the summit of the arch has descended to the level of our horizon and the marvelous system disappears from the sky; so that the inhabitants of those regions know nothing of it, and find themselves in a less favorable position to study their own world than we, who are nearly 800,- 000,000 miles distant.
During one-half of the Saturnian year the rings afford an admirable moonlight on one hemisphere of the planet, and during the other half they illuminate the other hemisphere ; but there is always a half-year
SATURN. 221
without " ringlight," since the sun illuminates but one face at a time. Notwithstanding their volume and number, the satellites do not give as much nocturnal light as might be supposed; for they receive, on an equal surface, only the ninetieth part of the solar light which our moon receives. All the Saturnian sat- ellites which can be at the same time above the hor- izon and as near as possible to the full phase do not afford more than the hundredth part of our lunar light. But the result may be nearly the same, for the optic nerve of the Saturnians may be ninety times more sensitive than ours.
But there are further strange features in this system. The rings are so wide that their shadow extends over the greater part of the mean latitudes. During fifteen years the sun is to the south of the rings, and for fif- teen years it is to the north. The countries of Sat- urn's world which have the latitude of Paris endure this shadow for more than five years. At the equator the eclipse is shorter, and is only renewed every fifteen years; but there are every night, so to say, eclipses of the Saturnian moons by the rings and by them- selves. In the circumpolar regions the day-star is never eclipsed by the rings ; but the satellites revolve in a spiral, describing fantastic rounds, and the sun himself disappears at the pole during a long night of fifteen years.
At one time it was supposed that the rings were solid, but they are now believed to consist of countless myriads of meteorites, each whirling in its own ap- pointed pathway round the monster planet.
As already said — leaving out of the question the
222 STORY OF THE SUN, MOON, AND STARS.
cloudy atmosphere — a man standing on the equator would see nothing of the rings. A man standing at the north pole or the south pole of Saturn could see nothing either, since the rings would all lie below his horizon. But if he traveled southward from the north
IDEAI, VIEW OF SATURN'S RINGS AND SATElyUTES FROM THE PLANET.
pole, or northward from the south pole, towards the equator, he would in time see the ringed arch ap- pearing above the horizon, rising higher and growing wider with every mile of his journey ; and when he was in a position to view the whole broad expanse, the transparent half-dark belt below, the wide radiant band
SATURN. 223
rising upwards over that, and the grayish border sur- mounting all, he would truly have a magnificent spec- tacle before him.
This magnificent spectacle is, however, by no means always visible, even from those parts of Saturn where alone it ever can be seen. The rings shine merely by reflected sunlight. Necessarily, therefore, while the sunbeams make one side bright the other side is dark ; and not only this, but the rings throw broad and heavy shadows upon Saturn in the direction away from the sunlight.
In the daytime they probably give out a faint shin- ing, something like our own moon when seen in sun- light. During the summer nights they shine, no doubt, very beautifully. During the winter nights it so happens that their bright side is turned away ; and not only that, but during the winter days the rings, while giving no light themselves to the wintry hem- isphere of Saturn, completely hide the sun.
When it is remembered that Saturn's winter — that is, the winter of each hemisphere in turn — lasts dur- ing fifteen of our years; and when we hear of total eclipses of the sun lasting unbroken through eight years of such a winter, with not even bright rings to make up for his absence, we can not think of Sat- urn as a tempting residence. The sun gives Saturn at his best only about one-ninetieth of the heat and light that he gives to our earth ; but to be deprived of even that little for eight years at a time, does indeed sound somewhat melancholy.
Looking now at the other side of the question, the possible inhabitants of the moons, especially those
224 STORY OF THE) SUN, MOON, AND STARS.
near at hand, would have splendid views of Saturn and his rings in all their varying phases. For Saturn is a beautiful globe, wrapped in his changeful envel- ope of clouds, which, seen through a telescope, are lit up often with rainbow tints of blue and gold ; a creamy white belt lying usually on the equator; while around extend the purple and shining and gray rings, some- times rivaling in bright colors Saturn himself.
We are compelled to assume that the continuous appearance of the rings is not due to real continuity of substance, but that they are composed of flights of disconnected satellites, so small and so closely packed that, at the immense distance to which Saturn is re- moved, they appear to form a continuous mass. There are analogous instances in the Solar System. In the zone of asteroids we have an undoubted instance of a flight of disconnected bodies traveling in a ring about a central attracting mass. The existence of zones of meteorites traveling around the sun has long been accepted as the only probable explanation of the periodic returns of meteoric showers. Again, the sin- gular phenomenon called the Zodiacal Light is, in all probability, caused by a ring of minute cosmical bodies surrounding the sun. In the Milky Way and in the ring-nebulae we have other illustrations of similar ar- rangements in nature, belonging, however, to orders immeasurably vaster than any within the Solar Sys- tem.
The moons of Saturn do not, like those of Jupiter, travel in one plane.
CHAPTER XIX.
URANUS AND NEPTUNE.
Tiiviv the year 1781, Saturn was believed to be the outermost planet of the Solar System, and nobody suspected the fact of two great, lonely brother-planets wandering around the same sun at vast distances be- yond,— Uranus, nine hundred millions of miles from Saturn; Neptune, nine hundred millions of miles from Uranus. No wonder they remained long undis- covered.
Uranus can sometimes be seen by the unaided eye as a dim star of the sixth magnitude. And when he was known for a planet, it was found that he had been often so seen and noted. Again and again he had been taken for a fixed star, and as he moved on, disappearing from that particular spot, it was sup- posed that the star had vanished,
One night, March 13, 1781, when William Her- schel was busily exploring the heavens with a powerful telescope, he noticed something which he took for a comet without a tail. He saw it was no mere point of light like the stars, but had a tiny round disk or face, which could be magnified. So he watched it care- fully, and found in the course of a few nights that it moved — very slowly, certainly; but still it did move. Further watching and calculation made it clear that, though the newly-found heavenly body was at a very great distance from the sun, yet it was moving slowly 15 225
226 STORY OP THE SUN, MOON, AND STARS.
in an orbit round the sun. Then it was known to be a planet, and another member of the Solar System.
From that day the reputation of Herschel rapidly increased. King George III, who loved the sciences and patronized them, had the astronomer presented to him ; charmed with the simple and modest account of his efforts and his labors, he secured him a life pension and a residence at Slough, in the neighbor- hood of Windsor Castle. His sister Caroline assisted him as secretary, copied all his observations, and made all his calculations ; the king gave him the title and salary of assistant astronomer. Before long the observatory at Slough surpassed in celebrity the prin- cipal observatories of Europe ; we may say that, in the whole world, this is the place where the most dis- coveries have been made.
Astronomers soon applied themselves to the ob- servation of the new body. They supposed that this "comet" would describe, as usually happens, a very elongated ellipse, and that it would approach consid- erably to the sun at its perihelion. But all the calcu- lations made on this supposition had to be constantly recommenced. They could never succeed in represent- ing all its positions, although the star moved very slowly: the observations of one month would utterly upset the calculations of the preceding month.
Several months elapsed without a suspicion that a veritable planet was under observation, and it was not till after recognizing that all the imaginary orbits for the supposed comet were contradicted by the observa- tions, and that it had probably a circular orbit much farther from the sun than Saturn, till then the fron-
Prominent Astronomers of Former Times.
228 STORY OF THE SUN, MOON, AND STARS.
tier of the system, that astronomers came to consider it as a planet. Still, this was at first bnt a provisional consent.
It was, in fact, more difficult than we may think to increase without scruple the family of the sun. In- deed, for reasons of expediency this idea was op- posed. Ancient ideas are tyrannical. Men had so long been accustomed to consider old Saturn as the guardian of the frontiers, that it required a rare bold- ness of spirit to decide on extending these frontiers and marking them by a new world.
William Herschel proposed the name of Georgium Sidus " the Star of George," just as Galileo had given the name of " Medicean stars " to the satellites of Ju- piter discovered by him, and as Horace had said Julium Sidus. Others proposed the name of Neptune, in order to maintain the mythological character, and to give to the new body the trident of the English mari- time power ; others, Uranus, the most ancient deity of all, and the father of Saturn, to whom reparation was due for so many centuries of neglect. L,alande pro- posed the name of Herschel, to immortalize the name of its discoverer. These last two denominations pre- vailed. For a long time the planet bore the name of Herschel ; but custom has since declared for the myth- ological appellation, and Jupiter, Saturn, and Uranus succeed each other in order of descent — son, father, and grandfather.
The discovery of Uranus extended the radius of the Solar System from 885,000,000 to 1,765,000,000 of miles.
The apparent brightness of this planet is that of
URANUS AND NEPTUNE. 229
a star of the sixth magnitude ; observers whose sight is very piercing may succeed in recognizing it with the naked eye when they know where to look for it. Uranus moves slowly from west to east, and takes no less than eighty-four years to make the complete cir- cuit of the sky. In its annual motion round the sun the earth passes between the sun and Uranus every 369 days — that is to say, once in a year and four days. It is at these times that this planet crosses the merid- ian at midnight. We can observe it in the evening sky for about six months of every year.
Everybody supposed that now, at least, the outer- most member of all was discovered. But a very strange and remarkable thing happened.
Astronomers know with great exactness the paths of the planets in the heavens. They can tell, years beforehand, precisely what spot in space will be filled at any particular time by any particular planet. I am speaking now of their movements round the sun and in the Solar System — not of the movements of the whole family with the sun, about which little is yet known.
Each planet has its own particular pathway; its own particular distance from the sun, varying at each part of its pathway ; its own particular speed in trav- eling round the sun, changing constantly from faster to slower or slower to faster, according to its distance from the sun, and according to the pull backwards or forwards of our neighboring planets in front or in rear. For as the orbits of all the planets are ovals, with the sun not in the middle, but somewhat to one side of the middle, it follows that all the planets, in the course of
230 STORY OF THE SUN, MOON, AND STARS.
their years, are sometimes nearer to and sometimes farther from the sun.
The astronomers of the present day understand this well, and can describe with exactness the path- way of each planet. This knowledge does not come merely from watching one year how the planets travel, and remembering for another year, but is much more a matter of close and difficult calculation. Many things have to be considered, such as the planet's distance from the sun, the sun's power of attraction, the planet's speed, the nearness and weight of other neighboring planets.
All these questions were gone into, and astronomers sketched out the pathway in the heavens which they expected Uranus to follow. He would move in such and such an orbit, at such and such distances from the sun, and at such and such rates of speed.
But Uranus would not keep to these rules. He quite discomfited the astronomers. Sometimes he went fast, when, according to their notions, he ought to have gone more slowly; and sometimes he went slowly, when they would have looked for him to go more fast, and the line of his orbit was quite outside the line of the orbit which they had laid down. He was altogether a perplexing acquaintance, and diffi- cult to understand. However, astronomers felt sure of their rules and modes of calculation, often before tested, and not found to fail. They made a guess at an explanation. What if there were yet another planet beyond Uranus, disturbing his motions — now drawing him on, now dragging him back, now so far balancing the sun's attraction by pulling in the oppo-
URANUS AND NEPTUNE. 23 1
site direction as to increase the distance of Uranus from the sun?
It might be so. But who could prove it? Hun- dreds of years might pass before any astronomer, in his star-gazing, should happen to light upon such a dim and distant world. Nay, the supposed planet might be, like Uranus, actually seen, and only be mis- taken for a "variable star," shining but to disappear.
There the matter seemed likely to rest. There the matter probably would have rested for a good while, had not two men set themselves to conquer the diffi- culty. One was a young Englishman, a student of Cambridge, John Couch Adams ; the other, a young Frenchman, Urbain Jean Joseph Leverrier, — both be- ing astronomers.
Each worked independently of the other, neither knowing of the other's toil. The task which they had undertaken was no light one — that of reaching out into the unknown depths of space to find an un- known planet.
Each of these silent searchers into the sky-depths calculated what the orbit and speed of Uranus would be, without the presence of another disturbing planet beyond. Each examined what the amount of disturb- ance was, and considered the degree of attraction needful to produce that disturbance, together with the direction from which it had come. Each, in short, gradually worked his way through calculations far too deep and difficult for ordinary minds to grasp, till he had found just that spot in the heavens where a planet ought to be, to cause, according to known laws, just such an effect upon Uranus as had been observed.
232 STORY OF THE SUN, MOON, AND STARS.
Adams finished his calculation first, and sent the result to two different observatories. Unfortunately, his report was not eagerly taken up. It was, in fact, hardly believed. L,everrier finished his calculation also, and sent the result to the Berlin Observatory. The planet was actually seen in England first, but the discovery was actually made known from Berlin first. The young Englishman had been beforehand, but the young Frenchman gained foremost honor.
It was on the 23d of September, 1846, that Le- verrier's letter reached the Berlin astronomers. The sky that night was clear, and we can easily understand with what anxiety Dr. Galle directed his telescope to the heavens. The instrument was pointed in accord- ance with Leverrier's instructions. The field of view showed, as does every part of the heavens, a multi- tude of stars. One of these was really the planet. The new chart — prepared by the Berlin Academy of Sciences, upon which the place of every star, down even to those of the tenth magnitude, was engraved — was unrolled, and, star by star, the heavens were com- pared with the chart. As the process of identification went on, one object after another was found in the heavens as engraved on the chart, and was of course rejected. At length a star of the eighth magnitude — a brilliant object — was brought into review. The map was examined, but there was no star there. This object could not have been in its present place when the map was formed. The object was there- fore a wanderer — a planet. Yet it is necessary to be excessively cautious in such a matter.
Many possibilities had to be guarded against. It
URANUS AND NEPTUNE. 233
was, for instance, possible that the object was really a star which, by some mischance, elnded the carefhl eye of the astronomer who constrncted the map. It was even possible that the star might be one of the large class of variables which alternate in brightness, and it might have been conceivable that it was too faint to be seen when the chart was made. Even if neither of these explanations would answer, it was still neces- sary to show that the object was now moving, and moving with that particular velocity and in that par- ticular direction which the theory of Leverrier indi- cated. The lapse of a single day was sufficient to dissipate all doubts. The next night the object was again observed. It had moved, and when its motion was measured it was found to accord precisely with what Leverrier had foretold. Indeed, as if no circum- stance in the confirmation should be wanting, it was ascertained that the diameter of the planet, as meas- ured by the micrometers at Berlin, was practically co- incident with that anticipated by Leverrier.
The world speedily rang with the news of this splendid achievement. Instantly the name of Lever- rier rose to a pinnacle hardly surpassed by that of any astronomer of any age or country. For a moment it seemed as if the French nation were to enjoy the un- divided honor of this splendid triumph. But in the midst of the paeans of triumph with which the en- thusiastic French nation hailed the discovery of Le- verrier, there appeared a letter from Sir John Herschel in the Athenceum for 3d October, 1846, in which he announced the researches made by Adams, and claimed for him a participation in the glory of the discovery.
234 STORY OF THE) SUN, MOON, AND STARS.
Subsequent inquiry has shown that this claim was a just one, and it is now universally admitted by all in- dependent authorities.
This, however, was of slight comparative impor- tance. The truly wonderful part of the matter was, that these two men could have so reasoned that, from the movements of one lately-discovered planet, they could point out the exact spot where a yet more dis- tant planet ought to be, and that close to this very spot the planet was found. For when, both in Eng- land and in Germany, powerful telescopes were pointed in the direction named — there the planet was. No doubt about the matter. Not a star, but a real new planet in the far distance, wandering slowly round the sun.
Here we have the discovery of Neptune in its sim- ple grandeur. This discovery is splendid, and of the highest order from a philosophical point of view, for it proves the security and the precision of the data of modern astronomy. Considered from the point of view of practical astronomy, it was but a simple exer- cise of calculation, and the most eminent astronomers saw in it nothing else ! It was only after its verifica- tion, its public demonstration — it was only after the visual discovery of Neptune — that they had their eyes opened, and felt for a moment the dizziness of the in- finite in view of the horizon revealed by the Neptu- nian perspective. The author of the calculation him- self, the transcendent mathematician, did not even give himself the trouble to take a telescope and look at the sky to see whether a planet was really there ! I even believe that he never saw it. For him, how-
URANUS AND NEPTUNE. 235
ever, then and always, to the end of his life, astronomy was entirely inclosed in formulae — the stars were but centers of force.
Very often I submitted to him the doubts of an anxious mind on the great problems of infinitude : I asked him if he thought that the other planets might be inhabited like ours, what might be especially the strange vital conditions of a world separated from the sun by the distance of Neptune, what might be the retinue of innumerable suns scattered in immensity, what astonishing colored lights the double stars should shed on the unknown planets which gravitate in these distant systems. His replies always showed me that these questions had no interest for him, and that, in his opinion, the essential knowledge of the universe consisted in equations, formulae, and logarithmic series having for their object the mathematical theory of ve- locities and forces.
But it is not the less surprising that he had not the curiosity to verify the position of his planet, which would have been easy, since it shows a planetary disk; and, besides, he might have had the aid of a chart, because he had only to ask for these charts from the Berlin Observatory, where they had just been finished and published. It is not the less surprising that Arago, who was more of a physicist than a mathematician, more of a naturalist than a calculator, and whose mind had so remarkable a synthetical character, had not himself directed one of the telescopes of the ob- servatory towards this point of the sky, and that no other French astronomer had this idea. But what sur- prises us still more is to know that nearly a year be-
236 STORY OF TH£ SUN, MOON, AND STARS.
fore, in October, 1845, a young student of the Uni- versity of Cambridge, Mr. Adams, had sought the solution of the same problem, obtained the same re- sults, and communicated these results to the director of the Greenwich Observatory, and that the astrono- mer to whom these results were confided had said nothing, and had not himself searched in the sky for the optical verification of his compatriot's solu- tion!
This was indeed a triumph of human intellect. Yet it is no matter for human pride, but rather of thankfulness to God, who gave to man this marvelous reasoning power. And the very delight we have in such a success may humble us in the recollection of the vast amount lying beyond of the utterly unknown. But while the rare mind of a Newton could meekly realize the littleness of all he knew, lesser minds are very apt to be puffed up with the thought of what the human intellect can accomplish.
Perhaps the chief feeling of lawful satisfaction in this particular discovery arises from the fact that it gives marked and strong proof of the truth of our present astronomical system and beliefs. Many mis- takes may be made, and much has often to be un- learned. Nevertheless, if the general principles of modern astronomy were wrong, if the commonly-re- ceived facts were a delusion, such complete success could not have attended so delicate and difficult a calculation.
We do not know much about these two outer plan- ets, owing to their enormous distance from us. Uranus is in size equal to seventy-four earths, and Neptune is
URANUS AND NEPTUNE. 237
in size equal to one hundred and five earths. Both these planets are formed of somewhat heavier materials than Saturn, being about as dense as water.
The size of the sun as seen from Uranus is about one three-hundred-and-ninetieth part of the size of the sun we see. To Neptune he shows a disk only one nine-hundredth part of the size of that visible to us — no disk at all, in fact, but only starlike brilliancy.
The Uranian year lasts about eighty-four of our years; and this, with a very sloping axis, must cause most long and dreary winters, the tiny sun being hid- den from parts of the planet during half an earthly life-time.
Uranus has at least four moons, traveling in very different planes from the plane of the ecliptic. Once it was thought that he had eight, but astronomers have since searched in vain for the other four, believed for a while to exist. Neptune has one moon, and may possess others not yet discovered.
Sir Henry Holland, the celebrated physician, and a devoted student of astronomy, has left on record an incident of his life connected with the planet Neptune of singular interest. I give it here, and in his own words, because it is scarcely likely otherwise to fall under the notice of astronomical readers. After stating that his interest in astronomy had led him to take ad- vantage of all opportunities of visiting foreign observ- atories, he says :
"Some of these opportunities, indeed, arising out of my visits to observatories both in Europe and America, have been remarkable enough to warrant a more particular mention of them. That which most
238 STORY OF THF, SUN, MOON, AND STARS.
strongly clings to my memory is an evening I passed with Encke and Galle in the observatory at Berlin, some ten or twelve days after the discovery of the planet Neptune on this very spot; and when every night's observations of its motions had still an espe- cial value in denoting the elements of its orbit. I had casually heard of the discovery at Bremen, and lost no time in hurrying on to Berlin. The night in question was one of floating clouds, gradually grow- ing into cumuli; and hour after hour passed away without sight of the planet which had just come to our knowledge by so wonderful a method of predic- tive research. Frustrated in this main point, it was some compensation to stay and converse with Encke in his own observatory, one signalized by so many discoveries, the stillness and darkness of the place broken only by the solemn ticking of the astronom- ical clock, which, as the unfailing interpreter of the celestial times and motions, has a sort of living exist- ence to the astronomer. Among other things discussed, while thus sitting together in a sort of tremulous impatience, was the name to be given to the new planet. Encke told me he had thought of * Vulcan/ but deemed it right to remit the choice to Leverrier, then supposed to be the sole indicator of the planet and its place in the heavens ; adding that he expected L,e- verrier's answer by the first post. Not an hour had elapsed before a knock at the door of the observatory announced the letter expected. Encke read it aloud; and, coming to the passage where Leverrier proposed the name of ( Neptune/ exclaimed, ' So lass den Na- men Neptun sein?
URANUS AND NEPTUNE. 239
It was a midnight scene not easily to be forgotten. A royal baptism, with its long array of titles, would ill compare with this simple naming of the remote and solitary planet thus wonderfully discovered. There is no place, indeed, where the grandeur and wild am- bitions of the world are so thoroughly rebuked and dwarfed into littleness as in the astronomical ob- servatory. As a practical illustration of this remark, I would add that my own knowledge of astronomers — those who have worked themselves with the tele- scope— has shown them to be generally men of tran- quil temperament, and less disturbed than others by worldly affairs, or by the quarrels incident even to scientific research."
The same reasoning which has been used in refer- ence to Jupiter and his moons, and to Saturn and his moons, might perhaps be applied also to Uranus and Neptune and their moons.
We know too little yet of their condition to venture far in such speculations. Still, taking the matter as a whole, there seem many reasons to incline us to the idea that each of the four greater outside planets may be a kind of secondary half-cooled sun to his satel- lites, helping to make up to them for the small amount of light and heat which they can obtain from the far- off sun.
CHAPTER XX.
COMETS AND METEORITES.
A CURIOUS discovery has been lately made. It is that some sort of mysterious tie seems to exist be- tween comets and meteorites. For a long while this was never suspected. How should it be? The comets, so large, so airy, so light; the meteorites, so small, so solid, so heavy, — how could it possibly be supposed that the one had anything to do with the other? But supposings often have to give in to facts. Astrono- mers are gradually becoming convinced that there cer- tainly is a connection between the two.
Strange to say, comets and meteorites occupy — sometimes, at least — the very same pathways in the heavens, the very same orbits round the sun. A cer- tain number of meteorite systems are now pretty well known to astronomers as regularly met by our earth at certain points in her yearly journey. Some of these systems or rings have each a comet belonging to it — not merely journeying near, but actually in its midst, on the same orbit.
Perhaps it would be more correct to say that the meteorites belong to the comet, than that the comet belongs to the meteorites. We tread here on uncer- tain ground; for whether the meteorites spring from the comet, or whether the comet springs from the meteorites, or whether each has been brought into
240
COMETS AND METEORITES. 241
existence independently of the other, no one can at present say.
Though it is out of our power to explain the kind of connection, yet a connection there plainly is. So many instances are now known of a comet and a meteorite ring traveling together that it is doubtful whether any such ring could be found without a comet in its midst. By and by the doubt may spring up whether there ever exists a comet without a train of meteorites following him.
Among the many different meteorite rings which are known, two of the most important are the so- called August and November systems. Of these two, the November system must claim our chief attention. Not that we are at all sure of these being the most important meteorite rings in the Solar System. On the contrary, as regards the November ring, we have some reason to think that matters may lie just the other way.
The comet belonging to the November system is a small one — quite an insignificant little comet — only visible through a telescope. We do not, of course, know positively that larger comets and greater meteor- ite systems generally go together, but, to say the least, it seems likely. And if the greatness of a ring can at all be