Hipparchus in the Observatory at Alexandria.
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 improvement. 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 enabling 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 astronomy 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 earnest and pleasant style, equally free, I think, from inaccuracy or unpardonable exaggeration. We have here the outlines of elementary astronomy, not merely detailed without mathematics, but to a very great extent 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 cultivation 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 expression, 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 discoverers 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 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, Schiaparelli, 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 intellectual “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 importance. 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 better than give his words. “If the time should evet 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 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 intellectual progress and culture of society. The story of the Kosmos is told by the authoress in her own language and after her own method. I believe, as I have said, the story is correct.
What is this earth of ours?
Something very great — and yet something very little. Something very great, compared with the things upon the earth; something very little, compared with the things outside the earth.
And as our journeyings 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 conditions 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” 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 overhead 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 and still, while sun, moon, stars, went circling round us once in every twenty-four hours, just for our sole and particular convenience. What an important personage man must have felt himself then in God’s great universe! Once again, we know better now!
The Solar System.
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, traveling 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 movement 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 seeing 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 consequence.
When I speak of the Universe, I mean the whole of God’s mighty creation as far as the stars reach. Sometimes 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 far the stars reach. We know now that there is no firm crystal covering over our heads, dotted with bright points here and there; but 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 flat 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 looking 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.
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 shining 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 noticed. 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 of Orion. Perhaps you also know the W-shape of Cassiopeia, 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 arranged by men into these groups, and who first gave them their names, we can not tell.
True, night by night, through century after century, they rise, and cross the sky, and set. But those are only seeming movements. Precisely as the turning 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 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 appear by night. Speaking generally, however, the stars remain the same year after year, century after century. The groups may still be seen as of old, fixed and unchanging.
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,” 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 constellation, and now in the middle of another. These restless 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 particular 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 between 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 insensibly 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, incompletely directed towards this center, and soon involving the whole mass in the same motion of rotation. The simplest form of all, even in virtue of this law of attraction, is the spherical form. It is that 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 circumference 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 situation near the plane of the solar equator, and their motions of translation round the same center, are explained by the theory which we are discussing. The most distant known planet, Neptune, would be detached from the nebula at the epoch when this nebula extended as far as the planet, out to nearly three thousand millions of miles, and would turn in a slow revolution requiring a period of 165 years for its accomplishment. 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, unrealizable, 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. Afterwards 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.
People began very early in the history ot the world to pay close attention to the sun. 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 questions 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 different 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 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 m1les. Ninety-three millions of miles! Can you picture that to yourself? Try to think what is meant by a thousand 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.