Ecce cœlum; or, Parish astronomy

Front matter

I w i

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UNITED STATES OF AMERICA.

Contents

I. Preparatory.

i USES 9

t. HISTORY 16

II. The Sky

II. The Sky.

i. ASPECT 33

2. NATURE 3 g

3. NATURE OF CONTENTS 43

4. ARRANGEMENT OF CONTENTS 49

SECOND LECTURE.

THE SKY.

I AM to explain what discoveries have been made in the distant sky. To do this to the best advantage, we must have a picture of the sky, with its leading aspects and names, fresh in our minds.

So let us imagine this structure unroofed, and, indeed, well taken down on all sides. And, to-night, let us further imagine that some tall Genius is kind enough to brush away with his besom the envious clouds — those ancient and unutterable enemies of the astronomer. We seem to be at the center of an immense hollow, half-globe, on the distant surface of which appear the heavenly bodies. If it were day, we should see on that remote concave the yellow sun : it being night, we see, instead, a multitude of stars and the moon with its silver crescent. Watch the host for a little behind some building, and you may satisfy yourself that they are all in motion towards the west ; that is to say, are all revolving about a

3 33 line drawn through where you are sitting and a point due north, but elevated about 40° above the horizon. Notice that very bright white star low in the west : that is Venus, named after the Greek and Roman goddess of beauty. Yonder, almost overhead, is another star, of scarcely inferior brightness but of more masculine hue: that is Jupiter, named after the king of the classical divinities. East of the zenith, about one third of the way down, you may perceive a much smaller star of ruddy light — Mars by name — appropriately called from the bloody god of war. Do you see that small star, just visible to the naked eye, almost on the eastern horizon ? Well, that is Saturn, named from the father of the principal gods, and sufficiently dim to represent one who is said to have had the very unfatherly and unhandsome trick of eating his own children. These stars, and many others which are never seen without a glass, are called planets, because they wander about greatly on the sky. Besides these, are certain other bodies, seen only occasionally, which are still greater wanderers — comets so-called, hairy stars — a denser part more or less bright, surrounded by a haze which often is found expanded into a pale streamer of prodigious length.

All others stars bear the name of fixed stars, because, to ordinary observation, there is little or no apparent change in their positions with

ASPECT. 35

respect to each other. Some of these bodies are very conspicuous, real princes for shining, and so, from time immemorial, have been honored with proper names. There, for example, is one nearly as brilliant as Yenus herself — Sirius — with a ray as frosty and keen as ever glanced from an iceberg ; another, Aldebaran ; another, Capella. Nearly half way up the northern heaven is a star by no means bright, but which has been on men's lips and in their eyes oftener than any other star whatever — the star by which ships have steered, and armies marched, and bondmen fled — the North Star. Count some twenty of the brightest of the fixed stars on the whole sphere : these astronomers call stars of the first magnitude. Count some sixty of the next brightest : these are of the second magnitude. Some two hundred of the next order of brilliancy : these are of the third. Six <%iers of magnitude are visible to the . naked eye : ten orders more include those seen by the telescope.

i Notice the unequal distribution of the stars on the sphere. Some are solitary, some in little groups and clusters, some in dense masses that resemble white clouds; while, among others, there seem no well-defined natural divisions — they seem sown broadcast and carelessly on the vault. That group of five stars forming the letter V is called the Hyades — rainy Hyades, said the ancients. That cluster £ little further to the west is the Pleiades — Job's Pleiades, with their sweet influences. And here, stretching across the whole hemisphere, like a white fog-bank with torches in it, is the well-known Milky Way which the old poets tell us was inadvertently made by Hercules when an infant. Other objects of the same general appearance are disclosed by the telescope in various quarters of the heavens — nebulae, so they are called.

These are natural divisions of the heavenly bodies. There are others not so natural, called constellations. The ancients (no one knows how ancient they were), with not a little help from the moderns, pictured the celestial sphere all over with figures of men and brutes and other objects, so as to show almost as extensive a menagerie as was collected in Noah's ark : indeed, the very ark itself is there ; at least Noah's dove, and we may reas^Sably suppose the ark to be not far off. There are bears and lions and domestic animals and birds and fishes and reptiles, interspersed with warriors and nymphs and centaurs and flying horses, all dovetailed into each other so as to include within their outlines nearly all the stars. If the leg or arm of a human figure could not be so disposed as to cover certain stars, a snake, under the sonorous name of Draco or Hydra, was slipped in to wind in and out till the crooked feat was accomplished. Yery seldom any resemblance can be traced between the constel-

ASPECT. 37

lations and the various objects after which they are called. But judge for yourselves. Around the North Star as a center, describe a circle that shall just touch the horizon. Within this circle are the Great and Little Bear, an immense Dragon, royal Cepheus with a crown on his head and a scepter in his hand, the helmed head and lifted falchion of Perseus, and on her chair, with a palm branch in her hand, queenly Cassiopeia. Would you think it? Around the point directly overhead, describe another circle that shall just touch the other. Within this new circle we have, towards the north, beauteous Andromeda, with fetters on her dainty hands and feet ; west, Pegasus, the winged horse ; over our heads, Aries the Ram ; next east, a sort of celestial Spain — for there is shaggy Taurus in full career with horns leveled at giant Orion, who, sworded and belted, with a lion-skin in one hand and a club in the other, is just in the act of dealing the monster a rousing blow between the eyes that will undoubtedly make him see stars. Could you have thought it — such dignified personages, such delightful nymphs, such illustrious heroes, such magical creatures, such stirring tourneys and bull fights, all up and down the arches of the sky ! However, these fanciful figures answer a very good purpose for classifying and describing the heavenly bodies. They distribute them into celestial nations and empires.

Provision is made for still further descrip tion of each celestial district, to any degree of minute accuracy that may be desirable. For many purposes, it is sufficient to tell what constellation a star is in. If we have occasion to be a little more precise, we can say in what part of the constellation it may be found, as in the neck of Taurus or head of Andromeda. To provide for still greater precision of statement, astronomers Have named the stars in each constellation according to their ^apparent brightness. The brightest is called after the first letter of the Greek alphabet, Alpha ; the next brightest, after the second letter, Beta; and so on through all the letters. When the Greek alphabet is exhausted, the Roman is used in the same wa} r . If both alphabets are not sufficient to take account of all the stars, our common numerals are resorted to. Thus we speak of Alpha Leonis, a Virginis, 61 Cygni. But it is not always enough, in making a map of a country, to draw its boundaries and set down within them the various cities and towns of all sizes, in something like their relative positions: some geographical purposes require that you state also their longitudes and latitudes; that is to say, their distances due east or west, and their distances due north or south of a given point on the earth. So, for some astronomical purposes, it is not enough to bound a given constellation and set down its stars in nearly their

ASPECT. 39

relative places, with their names. We requ re to know the longitude and latitude of each. star. We must know how far it is from a certain great circle drawn northerly and southerly on the sphere, and how far also from another great circle drawn at right angles to the other. From very remote periods, astronomers have been en gaged in getting this latter information. Hipparchus made out a catalogue of nearly all the stars visible to the naked eye at Alexandria, giving the latitude and longitude of each. Herschel, La Lande, Mayer, and others, have constructed similar catalogues, but giving the places of the stars with much greater accuracy.

We have before us a general picture of the celestial sphere, with the more usual names and classifications of the objects that shine upon it. I am now prepared to state what discoveries have been made. What is this seeming immense hollow globe of the heavens ? People once thought that the appearance was reality — that they were surrounded at a great distance by an immense shell of crystal, to which all the heavenly bodies were fastened. At a later period, most scholars thought there were several of these spheres: each carrying heavenly bodies, and each having a motion peculiar to itself. But now we know that there is nothing of the sort above and around us. The celestial sphere is nothing but indefinitely extended space, made to appear colored at times by the hue, and to appear rounde i always by the shape, of oir atmosphere. There is nothing solid yonder to which the celestial bodies can be attached. They are absolutely hung on nothing — though Milton ventures to take poetic license, and hang one orb, at least, by a golden chain. This idea of unsupported heavenly bodies was quite too hard for the remote ancients : they must have spheres, and, not a few of them, an elephant and a tortoise to hold up the earth and heavens. But, finally, it filtered through the apprehensions of people that such supporters must themselves need support quite as much as a star; also, that no one ever saw them, or otherwise credibly knew of their actual existence. So they were quietly dispensed with. And now nothing remains but the infinite space, which we certainly know to exist, and the stars which we certainly know to exist in it.

Popularly speaking, this great space which environs us on all sides, and contains the heavenly bodies, is empty. It is substantially a vacuum. The ancients said that Nature abhors a vacuum : if so, she has plenty of abhorring to do. There is no atmosphere pervading space : we could not breathe in its mid-intervals one single moment ; there is nothing there that our senses could perceive. As we ascend from the earth, wo find the air gradually become thinner ; and La- Place has shown, that, after a few miles, it must

NATURE OF THE CELESTIAL SCENERY. 41

cease entirely. Beyond that point, very large solid bodies, though moving with enormous velocity, are found to encounter not the smallest perceptible resistance. Their places, as computed on the supposition that they move in a vacuum, are such as we actually find them. At the same time, there is reason to believe that the vacuum may not be absolutely perfect. Certain facts which have come to light in late years have convinced many astronomers that we must allow the existence of an exceedingly dilute form of matter pervading space. It is nothing that we could detect in the ordinary, sensible way : we could not weigh it, nor see it, nor receive sounds through it ; could not feel it, should we strike our hands through it with our utmost force. Such a mere nothing is it. It is only when some very light body goes rushing through it, at the rate of thousands of miles an hour, that its presence becomes sensible in resisting somewhat the motion.

If we could visit mid-space, it would seem a perfect void, also dreadfully cold and dark and silent. The higher we go into our atmosphere, the colder it becomes. All mountain summits, above a few thousand feet, are covered with perpetual snow. Persons ascending in balloons at last reach a cold that is intolerable. They evidently approach the confines of an eternal winter,, that, for silence and motionless fierceness, laughs to scorn all that we have of arctic and antarctic.

According to the calculations of Sir John Her schel, we have only to go fifty miles from the earth's surface to reach — 132° Fahrenheit. Could we suddenly set down any moist thing at this point, it would instantly explode like a pistol, though without sound (for mid-space is soundless as well as matterless), and turn to stone as if touched by a magician's wand. And if, at this short distance from the earth and sun, space is so cold, what must it be in those remote vacancies where the sun shows as a mere star ? In thought, we sail away most comfortably among the constellations, without furs or overcoat ; and perhaps our fancies make nothing of stopping whole hours in mid-heaven, leaning against the chair of Cassiopeia, or grasping the horns of Taurus, to admire the glory of the trooping stars ; but one real bodily expedition of the sort would forever cure us of such fancies. Perhaps of some others also ; for, when our thoughts go yachting it through space, they are very apt to take with them, not only our genial parlor temperature, but also our pleasant earthly light and colors. But, in point of fact, the starry spaces are awfully dark. Those who visit the higher regions of our atmosphere, by mountains or balloons, tell us that the pleasant blue gradually passes into an intense black. At last, the stars glitter on a

NATURE OF THE HEAVENLY BODIES. 43

background of perfect jet. To an observer out in mid-heaven, the whole sphere would seem muffled in a horrible pall, save just at the points where the heavenly bodies are. He would have the impression of not being able to see an inch before him. He would see sun, moon, and stars all at the same time ; but they would look as if hissing on a sea of ink. The blackness would seem solid enough to be cut with a knife. An Egypt in the sky would seem to him to have completely overrun its Spain, and indeed its whole atlas of celestial empires. And should he try to express his feelings, and to say, " How awful is this blackness! " — "How glorious are these luminaries ! " — no sound, nor specter of a sound, could issue from his shouting lips.

Such is the " House I live in " of the heavenly bodies. What are the heavenly bodies themselves — what this sun, this moon, these planets and comets and fixed stars and nebulae?

In remotest times, very likely, men thought them distant heavenly torches, or openings of various sizes through the sky into an ocean of glory beyond. In process of time, they came to be very extensively regarded as intelligent beings — gods and goddesses, also human beings raised to the skies on account of illustrious merit, or, what was not always the same thing, the favor of the divinities. The sun was Apollo, god of fiery arrows ; the moon was Diana, goddess of the silver bow ; and so on, until the sky was one great Parliament House of deities in everlasting session. Worship was paid to the shining crowd ; to them incense rose, hymns were chanted, and victims bled. In civilized countries of modern times, people are far enough from such views of the nature of the heavenly bodies : multitudes do not even trouble themselves to have any views whatever on the subject. They have never put the question to themselves, " What are they — those bright lights above us ? " Accustomed to the sight from infancy, busied in their digging and buying and selling, it has never occurred to them to be curious as to the nature of those far-off luminaries. They are content to have the use of them — to work by the sunlight, to walk by the moonlight,. to steer, and perhaps to steal, by the starlight. In this respect, they are inferior to many in the remotest and rudest ages. And yet the question has long been well answered, and the answer is in possession of tens of thousands on all sides of them.

What are the heavenly bodies ! Not lamps, not apertures through which glory shines, not personages ; but immense masses of unintelligent matter, some self-luminous, and the rest shining by reflected light. It is found that the light coming direcly from a candle, or other sell-luminous object, differs by a certain property from the same light after it has undergone reflection. This fact enables us to ascertain easily that a part of the objects in the sky shine by reflected light, while the rest are self-luminous. The sun, and fixed stars, and nebulas are found to be self-luminous ; the moon, planets, comets, and zodiacal light shine only by the light that comes from these. If a man is confronted by what purports to be a ghost, he pronounces it well-authenticated flesh and blood just as soon as he sees that it casts a shadow.; so, just as soon as we find that the heavenly bodies emit and reflect light, we know that they are true matter; and, so far as we have been able to observe this matter, it has the appearance of that which composes our earth. If the moon is looked at through a telescope, we see a rugged surface of mountains and valleys. In regard to the other bodies in the sky, the glass does not serve us as well ; but the telescopic aspect of most of the planets gives none the less decidedly the impression of an earth-like surface. But the heavenly bodies are not only masses of earthy matter : they are masses of immense size. They look small to us, it is true — the sun and moon occupying no larger space in your eye than does the crown of your hat at the distance of a few feet, and most of the stars showing as mere needle-points.

They do look very small, most certainly ; but so the great earth would if we should go very far away from it. The earth is so large that we can travel upon it for months and years without crossing our track ; and yet, should we go off into space from it, this immense bulk would gradually lessen on the eye till at last it would appear no larger than the smallest star. Though the dog bays at the moon as if it were within hearing, though the savage thinks that he could almost bring down the sun with his arrow, though so intelligent a person as Yirgil tells us of a personage who brushed the stars with his sublime head, yet it is very easily discovered that the nearest of the heavenly bodies must be thousands and thousands of miles away. This is proved by the fact that only a few of them appear to change their places on the sky at all in consequence of any change, however great, in our position, and these few only in a very slight degree. A few steps will change the place on the heavens of some near objects a whole quadrant : but yonder mountain, twenty miles away on the horizon, would scarcely seem to stir should you walk an hour perpendicular to the line of its direction. Now, as to the heavenly bodies, it is found that one might travel thousands of miles on the earth, without shifting the apparent place of most of them on the vault in the slightest — without shifting the apparent place of any of them, save by a very trifling amount. So it is plain that they must be at a very great distance from us. Why, if a body were displaced on the sky to the am. unt of the moon's apparent diame* ter, by our going a thousand miles on the earth, it must be a hundred thousand miles away ; and there is not a body in the whole heaven that would undergo any thing like that displacement were we to remove such a distance. So we must conclude that all the heavenly bodies are immensely remote from us, and so of immense magnitude.

How are these great masses of matter actually disposed in space ? According to some principle of orderly arrangement, we should presume. The Supreme Cause is no friend to confusion. Still, what the celestial order really is, is not easily discoverable. There is, to first view, no system whatever in the distribution of large portions of the heavenly bodies. It is as if the Genius of disorder had sown them. In other parts, there are appearances of systematic arrangement; but then the question arises, Is the apparent arrangement the real one ? Can I say that two stars are actually near each other in space, because they appear near each other on the sky ; or that other two stars are remote from each other, because one appears in the east, while the other is seen in the west ? Not as long as I find, that, by putting myself between two trees only ten feet apart, I project them on directly opposite points of the heavens ; not as long as I find that the tree which is only ten feet from me, falls on the sky at the same point with yonder mountain which is twenty miles away. So there was no small difficulty in ascertaining the real plan among the celestial bodies ; and, in fact, it was not ascertained till after long ages of observation and study. But persuaded, as thinking men were, that there must be system everywhere within the domains of the Supreme Wisdom ; well aware, as most of them were, that apparent confusion, from unfavorable points of view, often covers a system of exactest order — they did not give over to inquire. At last they found the favorable stand-point which laid open the whole mystery of the celestial arrangements. The lamps of a city, as one approaches it some evening, appear a mere chaos of bright points ; and yet that city is Philadelphia, where streets cut streets desperately at right angles and all the lights gleam on the sides of perfect squares. And they seem so to the same man, when, turned aeronaut, his balloon has shot him up thousands of feet over the centre of the city. He has now found the true point of view. An army engaged in battle seems an inextricable maze to a looker-on from the same plain — men projected on and crossing men till all individual outlines are lost — and yet here are all the parts of a host, from corps to companies, each under its own leader, in unbroken array and admirable discipline, pressing forward on victory to the rhythm of exulting trumpet and drum as only Napoleon and Austerlitz know how to pour them along. And it seems so to the same man just as £Qon as, arrived at yonder lofty hill-top, he mingles with the Emperor's staff and looks down on the whole scene. He has now the true point of view. So, at last, astronomers have found their true point of view. They look from over the beaming city. They gaze down on the rushing army. And now the whole celestial economy of arrangement stands unfolded. What is it ? The system of arrangement is this : —

1. A body, not self-luminous, has one or more like bodies revolving around it. There are many such systems, which we will call satellite -systems*

2. Several of these primary systems form a still larger neighborhood, and revolve about a self-luminous body, like the sun. There are many such systems, which we will call planet-systems.

3. Several of these planet-systems form a still larger neighborhood, and revolve about a common point within it. There are many such systems, which we will call sun-systems.

4. Several of these sun-systems form a neighborhood still larger, and circulate about one point within it. There are many such systems, which we will call group-systems.

5. Several of these group-systems unite in a still larger neighborhood, and in revolving about a common point within it. There are many such systems, which we will call cluster -systems.

6. Several of these cluster-systems combine into ai_:ther system still grander, whose centre of motion is also common to all its members. There are many such systems, which we will call nebula-systems.

7. Finally, all the systems of space, composing one great neighborhood that embraces all other neighborhoods, revolve around one motion-centre of the creation. This we will call the universe-system.

You see that it is a wheel within a wheel. Certainly, the ' height of that last, all-embracing wheel is exceeding dreadful.' Each order of systems includes all the orders below it ; and each primary system has at least as many revolutions as there are different orders. It is very like the arrangement of human society. First, we have the elementary group of the family, revolving about the home ; then several families, making a town, revolving about its central village ; then several towns, making a county, revolving about its county seat; then several counties, making a State, revolving about its State capital ; then several States, making a nation, revolving about the national metropolis ; then several nations, making a world, revolving about the political centre of humanity, which once was Rome, which now is — shall we say London or Paris or St. Petersburg or Washington ?

Take another illustration ; for it is important to have this matter familiar. In these warlike times, i\ is hard to resist dealing in warlike ill ustrations : oesides, it may fairly be presumed that they will be understood with special facility. Imagine the encampment of a great army. On entering it, the order in which the tents are disposed does not readily appear. But, on examination, we find that there is a very rigid system of arrangement, and that this is it, First, the camp of the company about its captain, separated by a plain interval from all other company -camps. Next, expanding around this, is the camp of a regiment about its colonel, separated by a still more marked interval from all other regimentcamps. Then, expanding around the regiment, is the camp of the brigade about its brigadier, separated by an interval still more decided from all other brigade -camps. Further, expanding around the brigade, is the camp of the division or corps about its major-general, separated by an interval still broader from all other corps-camps. Lastly, expanding around the corps, is the whole encampment of the grand army about its general or marshal or monarch. See here a picture of the great encampment of the sky! I say "encampment ; " for, to one watching the sky for a short time, every thing seems stationary. But, really, the sky is not a camp. It is rather a glorious parade ground, full of motion, full of orderly, systematized motion — a flaming bannered field on which the various celestial powers are going through their various related evolutions under their respective leaders — companies of stars maneuvering under star -captains ; regiments, brigades, divisions, whole hosts of stars, manoeuvering under star- chiefs of as many ascending grades of rank and splendor. Hail, host of heaven ! Hail, glittering rank and file ! Hail, gorgeous commanders in golden mail, and shining far o'er the field ! Veterans all, though unscarred, as far as we can now see, — all hail ! for, as we shall soon find, such brilliant equipment, such skillful commanding, such perfect obeying, such complicate wheeling on exactest time and admirable step, was never seen in any terrestrial army.

But you would like the evidence that such is the arrangement of the heavenly bodies. It is observed that every thing on the earth is heavy. We never take up any thing about the earth, whether great or small, whether this sort of matter or that, without finding it to have more or less weight. That is to say, the earth attracts it, or it attracts the earth, or, perhaps, both mutually attract. Newton, on thinking the matter over (weknow how it happened, under the famous appletree, and how, as the apple came down, the thought of the philosopher went up) , concluded to adopt the last view, and to suppose that an attractive force, developing itself equally in all directions, and extending to all distances, belongs to every atom of matter, terrestrial and celestial. On the basis of this assumption, lie was able to prove, mathematically, that every body must attract every other body with a force proportioned directly to its own quantity of matter, and inversely to the square of the distance between the bodies. If you double the amount of matter in a body, you double its attractive force ; if you double its distance from another body, you quarter its attractive force on that body. With this law, he proceeded to demonstrate, by the most rigorous of mathematics, that, if two or more free bodies in space form a neighborhood, they must instantly rush together, or they must all revolve about their common centre of gravity ; meaning, by this common centre, that point among them where their several attractions just balance each other, so that a particle at that point would have no tendency to move. The fact that such bodies are found apart, after an existence of thousands of years, will then be proof that they are all revolving about their common centre of gravity. Hence, if several celestial bodies are found contiguous, as compared with others, we must infer that they form a system of revolution by themselves ; if several of these minor systems are found contiguous, as compared with others, we must infer that they compose a still larger revolving system ; and so on. Or, if we find certain heavenly bodies forming together a system of revolution, we must infer their relative contiguity to ea;h other in space. We need only to establish, by observation, the actual existence of either such celestial neighborhoods as have been described, or such related motions as have been described, in order to establish the existence of both. Now we can always do the one or the other.