Astronomical essays

Front matter

ASTEONOMICAL ESSA'

GEORGE

'C t%y.

Foreword

This volume of astronomical essays has been compiled from a series of articles originally published in the Boston Pilot over the pen-name of Catholicus. The series is here presented connectedly at the request of the Most Reverend Archbishop of Boston, who has graciously written the author, "I highly commend your articles on astronomy for publication in book form."

A new book on the science of the heavens needs no apology. There will always be found many, like Carlyle, eager to learn more and more concerning the occupants ot the sky. Even to persons only moderately interested in nature, must occur from time to time certain pertinent questions. Some will be curious to learn of the distance of the heavenly bodies. How far from us are those gleaming lights ? Are they our near neighbors, as they appear to be, or are they, on the contrary, many miles away? Again, what of their size? Are they but shining disks and points, or are they perhaps globes comparable to our great earth? Others will ask of their physical condition, whether it is like or unlike that of the earth ? What is the purpose of their being? And, above all, do they show signs of possessing living occupants? These, and kindred questions, will find an answer in the following chapters, especial emphasis being given to the important subject of the habitability of the heavenly bodies.

As will be observed , the series begins with a chapter on the shape of the earth. Some, reading the chapter,

^ Foreword.

may experience surprise that so much space has been allotted to a subject so simple and familiar. The topic has, however, been expanded advisedly, not only because it forms the starting-point of all astronomical inquiry, but because the fact of the earth's spherical shape is the initial wonder of the universe. Once we have realized that this great earth of ours is a globe set apart in space and suspended in mid-ether without support, with all that this signifies, we are prepared to accept the later affirmations that the earth is spinning on an axis and coursing through space about the sun. These and other cardinal truths of astronomy have undoubtedly long since become familiar. If the arguments in their favor are here set forth at considerable length, it is that the reader may know how firm are the fotmdations on which the science ot astronomy rests.

Besides the purely scientific chapters, drawn from systematic astronomy, there are others of a more apologetic trend. Their general purpose is to prove that neither the Christian religion nor the Catholic Church is in any way opposed to the science of astronomy or to its progress. In this vein are the chapters on the Astronomy of the Bible, that of the Fathers, and that of the Middle Ages, subjects not often treated, and seldom, if ever, gathered into the same volume. The modem era is even richer in material of apologetic interest. That Catholics have done their full share for the advancement of astronomy is set beyond doubt in the chapters on Copernicus, the Reform of the Calendar, and Recent Catholic Astronomers.

The most important portions of the book are those

Foreword. vn

that deal with the Case of Galileo and the Nebular Hypothesis. Not only popularly, but apologetically, these topics are among all that have been selected the chief in interest. They are rocks of offense on which the faith of many has suffered shipwreck. Special care has therefore been given to the handling of these two themes. The effect of the presentation will be, it is hoped, to remove misconceptions, to confirm the strong in faith, and to reassure the wavering.

Text-books on astronomy already abound. No better could be recommended to the interested reader than Newcomb's short Elements of Astronomy, published by the American Book Company. With this work and others of like character the present volume does not presume to enter into competition. It is meant rather as a book for general reading, for use in the library of one's home rather than for the school-room. Even as such, it has its limitations, of which the author is only too keenly conscious. He bespeaks it favor, nevertheless, because of the purpose it is intended to serve, the honor of God through the reverent study of the works of His creation.

The author wishes to acknowledge gratefully his indebtedness to Mr. James P. Sherry, a student at the Boston Seminary, for the chapter on Galileo as a Physicist.

Feast of the Resurrection, 1910.

TABLE OF CONTENTvS.

Chapter

I. Shape of the Earth

II. Relative Magnitude of Earth and Sun

III. Rotation of the Earth .

IV. Revolution of the Earth

V. Nicholas Copernicus

VI. The Planetary System .

VII. Nature oi the Sun .

VIII. Habitability of the Planets

IX. The Planet Mars .

X. Astronomy of the Sidereal World

XI. Habitability of Remote Planets

XII. The Bible and Astronomy .

XIII. The Bible and Star- Worship

XIV. The Miracle of Josue

XV. The Fathers and Astronomy

XVI. Astronomy in the Middle Ages

XVII. Reform of the Calendar

XVIII. Galileo as a Physicist

XIX. The Condemnation of Galileo

XX. Recent Catholic Astronomers

XXI. Fr. Secchi. Later Astronomers

XXII. The Nebular Hypothesis

XXIII. Theory of Laplace .

XXIV. The Nebular Hypothesis and Creation

XXV. Summary and Conclusion Appendix — Tables and Laws .

Page

IX

PRAISE OF THE CREATOR.

"The spacious firmament on high, With all the blue ethereal sky,

And spangled heavens, a shining frame, Their great Original proclaim.

"What though, in solemn silence, all Move round this dark terrestrial ball ;

What though no real voice nor sound Amid their radiant orbs be found ;

In Reason's ear they all rejoice, And utter forth a glorious voice.

For ever singing as they shine, The hand that made us is divine.' "

Joseph Addison.

ASTRONOMICAL ESSAYS.

Chapter I. The Shape Of The Earth

Some people find it strange that a study of the earth should be included in the science of astronomy. Is not astronomy, they ask, the science of the stars and heavenly bodies? Now, they argue, the earth is not one of the heavenly bodies; it is not located in the sky, it is right here under our feet. How, then, and by what twisting of words can it be given a place in astronomy?

And yet this globe of ours has its place in the science of the heavens and, indeed, a place of real importance. It would be anticipating too much to say thus early that our earth is a planet, like Venus and Jupiter and certain other bodies that are visible in the firmament. Before we are ready to accept this statement, much argument and proof will be needed. Told us in the beginning of our investigation, it is merely a vain assertion. But even from now and at the very inception of our studies, we can realize that the earth is the vantage-point from which alone it is given us to examine the myriads of lights that dot the heavens.

The Earth Our Observatory. All our inspection of the celestial bodies, all our measurement and analysis of them, must start from the earth as our viewpoint and centre. It is truly our astronomical observatory, from which alone we can measure the sizes, angles, and distances of the objects that people the heavens. Hence, before we can learn anything definite about the sun, the moon, and the stars, we have to understand our own earth and, above all, we need an accurate knowledge of its shape and size. If we start with a wrong conception of these, we shall be betrayed into innumerable errors regarding all astral bodies. This is the justification for beginning the present series of astronomical sketches with a chapter on the true shape of the earth.

Belief of the Ancients. All primitive peoples thought of the earth's surface as a flat, level plain, roughened, it is true, by hills and mountains and indented by valleys and ravines, but still in its larger aspects a level, horizontal expanse of land and sea. Indeed, is not this its obvious appearance? From any single post of observation, even if it be a mountain-top or the ocean with its unimpeded view, who would doubt that the earth is level, who would infer that it slopes away in the form of a curve? Even today there are some persons, — and we need not go beyond Boston to find them, — who still proclaim their belief in the flatness of the earth. We may charge them with being crassly ignorant. But how should we set about to refute them? The simple testimony of the senses seems to say that the earth is level. I may ride for a thousand miles in a railroad train from Boston to

Chicago and except for the sHght upgrades and downgrades due to intervening mountain slopes, I shall certainly think that I have been following a dead level line. Or I may cross the Atlantic in an ocean liner and in that long journey of three thousand miles never once realize that I am being borne around the surface of a sphere. Whether on land or sea, the earth seems a plain, and if I trust only to first appearances, I shall pronounce it such.

It must not surprise us, then, to learn that of old all men, even the wisest, conceived the earth's surface as a level plain. In the olden times, in the morning of the history of the race, people did not travel as readily as now; they had no cars or boats propelled by steam or electricity to whirl them from one place to another. They had for means of travel only their limbs, and beasts of burden like the camel and the horse. To voyage a hundred miles was for them a serious journey. They sojourned but little in foreign lands and among strange peoples, and in turn few strangers came among them. And when strangers did arrive from the distance of a few hundred miles they were said to have come from afar.

Geography of the Jews. How small, for example, was the portion of the earth's surface known to the early Hebrews! Their knowledge of geography was limited to the southwestern corner of Asia and the northeastern corner of Africa. Besides Palestine, the land of the promise, they knew of countries to the north verging towards the present Black Sea, of Egypt and Arabia to the south, and of Mesopotamia to the east. How narrow the boundaries that encompassed the then known earth! The Black Sea, the Mediterranean, the Nile River, a line stretched across Arabia from the upper Red Sea, and the Euphrates River to the east, these formed very nearly the uttermost boundaries of the earth as it was known to the ancient Jews. In this space were included only three bodies of water of considerable size, the Red Sea, the Dead Sea, and the Mediterranean, and of the latter they had explored only the eastern end.

With such limited knowledge (for which, however, to blame them would be puerile), how natural it was that they should think of the earth's upper surface as perfectly level. How far it stretched they did not know, and said no man could know. But wherever it ended, it took the form of a vast horizontal circle, and on this circular rim was supported the great vault of the sky. Down under the earth's surface were subterranean basins for supplying the rivers and oceans, and lower yet were what they called the great abysses, of unfathomable depth.

Jews' Superiority of Concept. Undoubtedly all early peoples had some such notion of the earth's shape and structure as had the Hebrews. If the question occurred to them what it was that supported this immense earth and held it up, they answered variously according to their lights and fancies. Most primitive peoples, as even the lettered Hindus and the cultured Greeks, thought fantastically of some monstrous elephant or of some giant Atlas supporting the world upon his shoulders. To the credit of the Hebrews be it said that they avoided all such myths and childish fantasies, attributing the upholding of all things to the word of God's power (Heb. i, 3). It was God who had set up the pillars of the earth (Ps. Ixxiv,

3). "He stretcheth the north over the empty place, and hangeth the earth upon nothing," such was the sublime and daring thought of the Book of Job (xxvi, 7) , one of the many true and exalted concepts that lift the Hebrew Scriptures above the writings of every other primitive people.

PTOLEMY'S STUDY OF THE QUESTION.

The first man who proved clearly that the earth is a globe was Ptolemy, the illustrious Grecian astronomer of the second century of the Christian era. When we read his arguments, we see that, as far as they extend, they are just as convincing as are our proofs of today.

Ptolemy's First Argument. Consider, for example, his argument of the manner in which a ship disappears as it recedes from the shore. If it were riding on a level, it would disappear from sight all at once, at the moment when our power of sight was now too feeble to follow it. But, as a matter of fact, it sinks from sight as if it were being swallowed up in a trough. The hull of the vessel disappears first, declining below the water's edge, but for some time after we may still see the decks, the masts, and the sails. These then disappear in the order of their height, the topmast and its sails last of all. To all appearances the ship has been gradually submerged. But were we on the ship instead of on the shore, we should still find our craft riding the waves in safety.

The only possible explanation of the gradual disappearance of the vessel part by part, is that she has been following not a horizontal line but a line bent away from the horizontal in the form of a continuous curve, and that in this instance at least the ocean's surface is not level but curvilinear. The observations of Ptolemy made at Alexandria in Egypt eighteen hundred years ago, can be easily repeated by us in Boston Harbor or Massachusetts Bay in the present year of grace and with the same results. Indeed they can be repeated on any and every ocean, sea, or large lake throughout the world. The earth, then, is nowhere fiat as its first appearance indicates, but everywhere slopes away from a level in the form of a circular arc.

Argument from the Stars. Ptolemy's second argument, though not so simple, is however equally cogent. It rests on the change in our starry heavens as we alter our position on the earth to some different degree of latitude. As we move to the southward, for example, particularly if our journey covers many miles, new stars and constellations appear above our southern horizon and the old ones are displaced. From Boston we are never privileged to behold such brilliant constellations as the Centaur and the Southern Cross. But let us travel southward to the Tropic Zone, then these glittering groups of southern stars will rise above the margin of the sky.

It must be that our southern horizon has been depressed so low as no longer to act as a screen between us and them. Were the earth level, the horizon would hold its direction and position relative to us and these southern stars, and would continue to conceal them from our view. To the earlier readers of Ptolemy this argument meant more than it does to most of us. For in his time people made a practice of observing and studying the stars, and were quite familiar with their names and groupings. Among the city-bred people of modern times there are very few who watch the stars and come to know their names and relative positions. The more's the pity, for they thus remain in ignorance of the details of that wonderful design which the Creator has imprinted on the heavens.

After Ptolemy. In view of the undoubted cogency of Ptolemy's twofold argument, how came it, we may ask, that in the Middle Ages so many doubted the sphericity of the earth, continuing to believe that its upper surface formed a level plain? Arguments from the Hebrew writings and a misunderstanding of their scope undoubtedly had some effect in counterbalancing the weight of Ptolemy's reasoning. There was moreover the apparently clear testimony of the senses that the earth is a fiat body and not round. So throughout the medieval period some inclined to one belief and some to its opposite. It was a period of uncertainty as far as this particular problem was concerned, and the uncertainty was not finally dispelled till in the year 1521 the crew of Magellan, the Portuguese Catholic, accomplished the circumnavigation of the globe.

PRESENT LISTING OF THE ARGUMENTS.

In our present manuals of astronomy many separate lines of argument are traced, each going to show that the earth is of spherical form. Among these the four most striking may be summarily indicated as follows : First there is given Ptolemy's argument from the manner of a ship's disappearance at sea, as developed above.

Eclipses of the Moon. Secondly, eclipses of the moon afford a new ground for the inference that the earth's shape is spherical. Not infrequently, as a rule once or twice in every year, the full moon is eclipsed either wholly or in part by passing into the shadow of the earth. That it is the earth's shadow which causes the eclipse, there is not the slightest room for doubt. In every lunar eclipse then, we can witness the earth's shadow projected on the moon's surface just as truly as in other circumstances we can observe on the ground the shadow of a tree or building.

Now the shadow on the moon is always a circle or the segment of a circle, and this holds true for all eclipses no matter in what direction from the earth the moon be placed, whether over the eastern or the western hemisphere. From this it follows that the boundary of the earth is in its every part of circular form. For a shadow reproduces correctly the outline of the original as we plainly see in the case of a tree or building. We conclude, therefore, that if the earth's shadow is circular its boundary and contour must be circular also. And the only possible form of an object that will appear circular from whatever side it be viewed is the globular or spherical.

Analogy With the Heavenly Bodies. A third argument for the sphericity of the earth is that derived from analogy with the heavenly bodies. We know that the sun is a globe and that the moon is one as well. So, too, the planets. Mercury, Venus, Mars, and the rest, when viewed through a telescope, are seen to be quite evidently of spherical figure. Indeed the spherical is the usual and perhaps the universal form in inanimate nature, if the larger bodies alone be considered. By analogy we should infer that our earth also is a globe. For in nature throughout its length and breadth all things follow common laws. Their unity of structure is indeed a proof of the unity of their Creator.

Circumnavigation of the Globe. Fourthly and finally, the earth is proved to be a sphere by the fact that it has been sailed around, first by the crew of Magellan, the Catholic, in the memorable voyage lasting from 1519 to 1521. Parenthetically it may be interesting to us of the United States to learn that this daring expedition of discovery was halted for a long time in the Philippine Islands and there, in a land now our colonial possession, Magellan himself, the commander, went to his death and lies buried. Many times since and in many different directions has the earth been circumnavigated, so that there is now abundance of observational proof as well as argument of mere reasoning to convince us that the earth is round.

Why Not Accepted Earlier? Once more may occur to us the wonder that the true shape of the earth was not earlier recognized. For it is now one of the most patent facts of science. But transporting ourselves back to the Middle Ages, we may easily realize how the above arguments failed of their effect. The fourth argument was not yet available. Till Columbus crossed the Atlantic, Europeans knew of no hemisphere other than their own. To the west and to the far east all was mystery. The first argument, that of Ptolemy, was well enough for determined localities. But who would assure the earlier people that the asserted phenomenon would hold good at every seacoast and every lake-border? It was an argument from induction and the induction was not yet sufficiently complete.

The argument derived from eclipses of the moon was probably never offered for their consideration, surely not with all its present force. Lunar eclipses were for them mysterious phenomena, attributed by some indeed to supernatural causes; and they would find it hard to believe that the shadow of the great earth could be so diminished as barely to cover the face of the moon. Finally the spherical figure of sun, moon and planets, even if fully assured to them, would scarcely suggest to their minds that the earth must have a corresponding form. For the heavenly bodies were placed by them in one category, the earth in another. The former were ethereal objects of strange substance moving lightly in the upper atmosphere; the earth was terrestrial, made not of fire but of land and water, God's footstool and the centre of the universe.

For all these reasons the world for centuries doubted or stood divided between two opposite opinions, one that of Ptolemy, founded on rational argument and asserting the rotundity of the earth, the other founded on sensible appearances and maintaining that at least the upper and habitable surface of the earth forms a level plain.

Conclusion. And now if a sceptic approaches you, young scholar, on Boston Common or elsewhere, and argues that the earth is not round like the globe in your schoolroom but flat like the maps in your geography, perhaps you will be able to refute him. Tell him of the ship disappearing part by part below the horizon; tell him of the earth's circular shadow that covers the disk of the moon; point out to him the sun and moon and planets and let him say if these are not rounded bodies, and remind him of Magellan's trip around the globe. Submit to him finally that his error has been to mistake appearances for reality. "Things are seldom what they seem." Reason must ever be invoked to correct the misleading evidence of the senses. And in no department of knowledge will this correction be more often necessary than in the science of astronomy. For this in part has God given to man the noble faculty of reason. And it has been a part of God's providential plan, so proves the history of thought, to establish the worth of reason by guiding it gradually to a fuller knowledge of His visible creation.

Chapter II. Relative Magnitude Of Earth And Sun

In the panorama of the heavens as witnessed from the earth, the most impressive single object is undoubtedly the sun. Of all celestial bodies it is, or at least appears to us, the largest and the brightest. It makes our day and creates our seasons. When it shines, it dominates the heavens, putting to flight the other heavenly bodies almost without exception. In the starry realms it is the sun that seems to reign supreme. Supreme, therefore, must be its place in the science of astronomy. What sort of body is this brilliant orb, what is its distance from the earth and how great its size, these are evidently among the very first questions that astronomy must, if possible, answer.

In our present inquiry let us select for consideration the last-mentioned of these problems, that, namely, of the sun's volume or magnitude. Comparing sun with earth, let us seek to learn which is the larger body of the two, and whether they are almost alike or on the contrary far apart in size.

The Seeming Answer. At first view the answer to these queries seems ridiculously easy. For while the sun is evidently the mightiest of the heavenly bodies, when compared with the earth it seems to sink to a place of insignificance. Is it not after all merely a light, brilliant and resplendent and dazzling, to be sure, but still a mere disk of light, so small that with our vision we can compass it all at once from end to end? Brightest of luminaries, yes, and yet so far from filling the sky that it would take hundreds of similar disks to cover the heavens even along one line.

MAGNITUDE OF THE EARTH.

And now behold under the sky this earth of ours, broad, expansive and seemingly unconfined, to all appearances as spacious in length and breadth as the firmament itself! With this wide earth, who thinks of comparing that narrow circle of light? It seems to me that could I seize that luminous ring and draw it down, I might find space for it on a certain round table in my dining hall.

Comparison Seems Absurd. Compare the sun's size and the earth's — someone is heard to say contemptuously — the very idea is preposterous. For do I not know that it takes days and days to travel from one coast of our continent to the other, even by the fastest express, and that to cross the succeeding ocean demands another week or even weeks? And do there not remain other continents to traverse broader than our own, and a second ocean to cross before home is reached again? Perhaps Jules Verne was not far from right in his guess when he chose as title for one of his fanciful stories, "Round the World in Eighty Days." Journey a little away from this favored city that we smugly call the Hub, and we shall learn to our confusion of what tiny dimensions it is when compared with the entire wheel's vast circumference.

And yet through all our journeyings the sun grows no larger. It remains forever the same small disk of light, only a millstone in breadth, and we could find many a nook and comer of this great world that we call the earth where it could be tucked away and made to sink from sight.

True Greatness of the Earth. Such is the verdict we arrive at if we trust to appearances alone. And respecting one of the two bodies compared our verdict is correct and stands justified by the facts. The earth, our residence, is indeed a body of no mean dimensions. It is by itself a world, a universe, spacious enough to accommodate with room to spare the thousands of millions of human beings who now inhabit it, vast enough to have been the sole theatre of action for all the myriad events of human history.

Once on a time its western boundaries were the pillars of Hercules towering above Gibraltar's straits. Then they were moved farther on, to San Salvador, and later to the Golden Gate of the Pacific Coast. Then they advanced six thousand miles across an island-dotted ocean to the rich empire of Japan. Only then had far Cathay been reached from the east which Marco Polo in the thirteenth century had reached overland from the west. West and east had met and were one.

Earth's Greatness and Our Littleness. The globe had been encircled and what a mighty sphere it was ! 25,000 miles in extent its girdle, so the measurements told us, and its diameter through the earth's centre, from rim to rim, a round 8,000 miles. Our deepest mines, our profoundest excavations, scarcely exceed one mile. Shall ever the remainder of the vast interior be explored? We skim the surface, we make here and there a dent, and we fondly think we have completed the exploration of the earth and have nothing more to learn. But now and then an earthquake or a volcanic blast rends the crust and confounds the littleness of our science. Mother Earth reveals her own immensity. Yes, such is the earth, a mighty body, constructed on a scale so vast that nature's most awful cataclysms cause her no lasting injury, but leave her stable as before. When the fiery storm has passed, she can still boast her unshaken continents and her everlasting hills.

The Sun a Rival in Greatness? But high above the earth shines on the refulgent sun. He, too, is everlasting, is he not, like the earth in his age and in his youthfulness. The same luminary that shines on us lit up the earth for our remotest ancestors. And ages before they came, in the dim past when only vegetative life clothed and peopled the earth, the sun was already at his post sustaining the life which, without him, must have perished. Sustaining, did we say? Is it then true that our earth owes such dependence to the sun? Can it be possible after all that the sun is the more important and the mightier body of the two? Wait and we shall see.

EARTH'S DEPENDENCE ON THE SUN.

It needs but little observation to tell us that the earth depends upon the sun in many different ways. Even the most casual and inattentive of observers can see that the sun is our greatest natural source of light and heat, and the essential condition of all terrestrial life. It is truly the agent set in the heavens by the Creator for supplying the earth with warmth and light, and the requisites of life. It is at once the light-giving and the heat-giving body, and the life-giving body as well, if life be taken merely as a phy sical phenomenon.