Sun, moon, and stars. Astronomy for beginners

Front matter

TOTAL ECLIPSE OF THE SUN, 1860, FROM TARRAGONA.

St.N, Moon and Stars.

SUN, MOON, AND STARS.

Preface To Revised Edition

In the course of even a few years changes of necessity take place in so progressive a science as Astronomy. Some new discoveries are made, some new ideas are started, some old beliefs have to be given up. When the twentieth thousand of the English edition of " Sun, Moon, and Stars" was called for, it seemed to me that the time had come for a thorough revision of the whole : for a bringing up of the information contained therein, as far as possible, up to date.

In the carrying out of this aim no trouble has been spared, and able friends have generously given time to helping me. Many old passages have been omitted and many new ones interpolated, large portions of chapters have been rewritten, and the two last chapters are almost fresh ones. My little book will, I hope, go forth replenished with new vigor for a new campaign.

AGNES GIBERNE.

Worton House,

Eastbourne, December, 1892.

Preface

The pages of this little book 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 little book on Astronomy suited to beginners V I think that just such a

6 Preface.

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 any considerable inaccuracy or any 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 am inclined to 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, its cultivation 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

Preface. y

lie well within the general comprehension, and perhaps 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 little 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 re-

8 Preface.

corded — 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 the forms and pictures in the main 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, and in support of the remark I shall quote from the pages of a work recently published by the Professor of Poetry in the University of Oxford : " Every new province of knowledge which science conquers, poetry may in turn enter into and possess. But this can only be done gradually. Before imagination can take up and mould the results of science these must cease to be difficult, laborious, abstruse. The knowledge of them must have become to the

Preface. 9

poet himself, and in some measure to his audience, familiar, habitual, spontaneous. And here we see how finely science and poetry may interact and minister to each other .... Some beginning of such a reconciling process we may see here and there in those poems of ' In Memoriam,' in which the Poet Laureate has finely inwrought new truths of science into the texture of yearning affection and spiritual meditation ...."*

Wordsworth in one of his prefaces has stated so clearly the truth on this subject that I cannot do better 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 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

* " On Poetic Interpretation of Nature," by J. C. Shairp, LL. D., Edinburgh. David Douglas, 1877.

io Preface.

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 those above stated that I heartily commend this little book to the attention of those of my countrymen and countrywomen 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, after her own method, and with no guidance of mine : in the main, I believe, as I have said, the story is correct; but I must disavow the responsibility of every detail.

C. PRITCHARD.

Oxford, September 2, 1879.

Author's Preface

Little remains to me, as needing to be said about my little book, after the most kind words of Prof. Pritchard.

For years past I have had it in my mind to endeavor to supply some day, so far as might be, that of which there appeared to be a serious want — a plain and easily-to-be-understood Introduction to Astronomy. My wish has been to make it, not merely a text-book for school use, though possibly it may serve for that also, but a volume of sufficient interest for general reading ; not merely a book adapted for intelligent boys and girls, though I hope it may be found serviceable for them also, but a volume fitted for " beginners " of all kinds, whether children, working-men, or even grown people of the educated classes, who should have a desire to enter for the first time on the study of this fascinating science. The attempt, such as it is, has been at last accomplished.

12 Author s Preface.

I trust that a second underlying object or thought may not be found to have been altogether fruitless. In the Book of Nature, side by side with the Book of Revelation, we may learn some things about our Father in heaven. It would be happiness to feel that I had helped any, however slightly, to look upward through nature unto nature's God.

I have, lastly, to express my warm gratitude to Prof. Pritchard for the time and trouble he has so generously expended in looking through the proof-sheets of a work by one who, as a perfect stranger, had and could have no manner of claim upon him. A request made through a mutual friend, with doubt and uncertainty on my part, has met with a fulness of response and kindness utterly unexpected, and for which no words of thanks seem half sufficient.

Eastbourne, September 5, 1879.

Part I

I. THE EARTH ONE OF A FAMILY 17

II. THE HEAD OF OUR FAMILY 28

III. WHAT BINDS THE FAMILY TOGETHER? 41

IV. THE LEADING MEMBERS OF OUR FAMILY. — FIRST GROUP-- 55 V. THE LEADING MEMBERS OF OUR FAMILY.— SECOND GROUP 65

VI. OUR PARTICULAR FRIEND AND ATTENDANT 76

VII. VISITORS 88

VIII. LITTLE SERVANTS 96

IX. NEIGHBORING FAMILIES IO5

X. OUR NEIGHBORS' MOVEMENTS Il8

Part II

I. MORE ABOUT THE SOLAR SYSTEM I35

II. MORE ABOUT THE SUN 149

III. YET MORE ABOUT THE SUN 162

IV. MORE ABOUT THE MOON 172

V. YET MORE ABOUT THE MOON l82

VI. MERCURY, VENUS, AND MARS I94

1 4 Contents.

VII. JUPITER 209

VIII. SATURN 219

IX. URANUS AND NEPTUNE 227

X. COMETS AND METEORS 236

XI. MORE ABOUT COMETS AND METEORS — 244

Part III

I. MANY SUNS 257

II. SOME PARTICULAR SUNS 266

III. DIFFERENT KINDS OF SUNS 278

IV. GROUPS AND CLUSTERS OF SUNS - 287

V. THE MILKY WAY ___ 296

VI. READING THE LIGHT 307

VII. FURTHER THOUGHTS . 317

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Sun, Moon, and Stars.

Chapter I. The Earth One Of A Family

" The heaven, even the heavens, are the Lord's : but the earth hath He given to the children of men." — Psa. 115 : 16.

What is this world 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 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-by altogether to our old home. We must linger about her for a

Sun, Moon, <?tc. 2 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 centre 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 centre 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 centre 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 the great Universe !

Once again, we know better now !

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, travelling 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.

Speaking now of the Universe, I mean thereby the whole material 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 cannot 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, amid innumerable 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. We find this wonderfully described in the Bible, long before men knew or could know what

the words meant : " He stretcheth out the north

* over the empty place, and hangeth the earth

UPON NOTHING."*

When you look up into the sky from England, 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 England's "down," and England's " 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 centre 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. *Job 26 : 7.

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 before going 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 Wshape 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 cannot 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 cannot be seen in winter ; and some come into view in winter which cannot 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. And as he passes from point to point of his pathway through the constellations, he 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 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 apparently 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

26 Sun y Moon, and Stars.

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 his own radiant dazzling light; whereas a planet shines by light reflected or borrowed from the sun'

28 Sun, Moo7t y and Stars.

Chapter II. The Head Of Our Family

" The sun, which . . . rejoiceth as a strong man to run a race." — PSA. 19:4, 5.

People began, very early in the history of 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 -two millions of

MILES.

Ninety-two 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.

To reach the thought of one million, you must picture one thousand times one thousand. Our earth is about twenty-five thousand miles round. If 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 travelled about twenty-five thousand miles.

But that would be a long way from a million miles. You would have gone only once round the earth. Now a rope one million miles in length could be wrapped, not once only, but forty times, 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-two times as much again. So, to picture clearly to ourselves the actual meaning of " ninety -two millions of miles " is not easy.

Suppose it were possible to lay a railroad from here to the sun. If you could journey thither in a perfectly 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 just about three hundred and fifty years.

Thirty miles an hour is a slow train. Suppose we double the speed, and make it an express train, rushing 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-five years. If you had quitted this earth early in the reign of King George I., never stopping on your way, you would be just now, in the year 1893, arriving at the sun.

So much for the sun's distance from us. Now as to his size.

I have alread)^ mentioned that our earth's diameter — that is, her through measure, as, for instance, the line drawn straight from England through her centre 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 sixty - five thousand miles ?

The one is eight thousand miles, the other is eight hundred thousand miles !

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 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.

It would take more than twelve hundred thousands of little earths like ours, rolled into one huge ball, to make a globe as large as the sun.

Suppose our earth were to dwindle down and down, smaller and smaller, till she became a tiny globe only one inch in diameter. Imagine the sun at the same time dwindling down in the same manner, and keeping the same proportion as to size. " Keeping the same proportion " means that he would still be twelve hundred thousand times as large as the earth, that his axis, or the straight line through his centre from North Pole to South