Part 6

At a first glance at the starry firmament the stars seem pretty regularly distributed; nevertheless, look at that whitish, undecided, vapory glimmer which girdles the heavens as with a belt. It is the Milky Way. As we approach the borders of this star-cloud in our inspection, the stars appear more and more crowded together, and most of them so small that the eye can scarcely distinguish them. The accumulation of stars in the direction of the Milky Way is more especially visible when we examine the heavens with the aid of a powerful telescope.

The Milky Way itself is nothing more than an immensely extended zone of stars, that is, of suns, since each star, from the most brilliant to the faintest, is a sun.

Here, then, is an immense group, a gigantic assemblage of worlds, which seems to embrace all the universe, if it be true that the greater number of the scattered stars situated out of the Milky Way nevertheless form part of it. In reality, this multitude of millions of suns is divided into numerous and distinct groups, and those into others still more restricted in number, each composed of two or three suns.

What breadth of space does each of these groups occupy? What is the measure of the space which holds them all? The most powerful imagination in vain attempts to answer these questions intelligibly; here numbers fail us.

Let us add—a fact well proved, and one which will seem strange to many—

Our sun himself is a star of the Milky Way.

In examining attentively every part of the starry vault, a keen eye perceives here and there whitish spots resembling little clouds. One would say they were so many patches detached from the Milky Way, from which, however, they are often very distinct and very distant. The telescope discovers by thousands those cloud-patches, these—to give them their astronomical name—Nebulæ.

It was formerly imagined that each of these star-clouds was nothing more than an accumulation of stars, very close together, and very numerous—so many Milky Ways lying outside our own, and for the most part so distant that the most powerful instruments were able only to distinguish a confused glimmering. One of the most important observations of modern times, however, has shown that many of these nebulæ, including the most glorious one in our northern hemisphere—that in the sword-handle of Orion—are but masses of glowing gases.

Others, again, of these cloud-like masses—cloud-like by reason of their distance—show us, faintly shining on a background of apparent nebulæ, brilliant stars, larger no doubt, or more brilliant, than their fellows, and some of these objects called “Star-Clusters,” which are nearest to us, are among the most glorious objects revealed to us by our telescopes.

Let us attempt now to conceive what fearful distances separate these archipelagoes of worlds from our own!

Unfathomable abysses whose unspeakable depths the most powerful telescopes increase indefinitely! Profound, endless, bottomless, but lighted up by millions of suns!

Such appears to us the universe from the natural observatory where we are placed. But to obtain a more complete idea of its constitution, of the infinite variety of its members, we must descend from those regions, where the sight and mind are lost, to a group, nearer to us, and therefore more accessible to the investigations of man—to that group, or system, of which the earth forms part.

Of this the sun is the centre.

Round this focus of light and heat, but at various distances, revolve more than a hundred secondary bodies—Planets, some of which are accompanied by smaller ones—Satellites. Not self-luminous, they would be invisible to us, if the light, which they receive from the sun, were not reflected toward the earth, making them also appear as luminous points spread over the celestial vault like so many stars. Such would be the appearance of the earth seen in space, at a distance sufficiently great.

A common character distinguishes all the celestial bodies that form part of this group—the Solar System—from the multitude of other stars. For while the suns, composing what is called the Sidereal Universe, are situated at distances seemingly infinite, the bodies composing the group of which we speak are relatively much nearer the earth, are, in fact, our neighbors.

What results from this double fact? Two very simple consequences, easily understood.

The first is, that the stars do not undergo any sensible change of position in the starry vault. Their distance is such that they appear actually at rest in the depths of space; hence the term Fixed Stars—now abandoned, because a minute and elaborate study of their relative positions has established the fact that the stars really do move in the remote regions of the heavens. The apparent immobility of which we have spoken, and which is one of their characteristics, is evidenced by the uniformity of appearance preserved for centuries by the artificial groups of stars, to which the name of Constellations has been given.

Now, it is otherwise with the bodies that revolve round our sun: they are near enough to the earth to allow of their displacements in space being perceived in short intervals of time. Traveling, by virtue of their proper motions along the starry vault, distances which appear greater as their own distance from us is less, these bodies received at the outset the name they have since retained—Planets, or Wandering Stars.

It is thus that, when we stand in the middle of an extensive plain, we judge distant objects—those that border the horizon—to be immovable; while we instantly perceive the slightest change of place in the near ones. It is true that when we ourselves move, the real movements become complicated with the apparent movements, but the former must be distinguished, if we wish to have an exact idea of the actual course traveled. This complication of the apparent movements of the planets—a necessary consequence of the movement of the earth—is one of the most striking testimonials to the reality of the latter; but it must also be added, that this was precisely the stone of stumbling of ancient astronomy until the time—and that not long ago—when the real movements were made known. Movements of rotation, movements of revolution, around the common centre, the duration of these movements, distances, forms and dimensions, distribution of light and heat, all change in passing from one planet to another. And yet, marvelous thing, the same laws govern, all in such a way that the unity of plan is not less marked than the astonishing variety of the phenomena.

One circumstance common to all the bodies of the solar system forcibly strikes the imagination. It is, that these enormous masses—these globes, many of which are much heavier than the earth, and lastly, the earth itself—are not only suspended in space, but move through the ether with velocities truly stupendous.

Imagine yourself a spectator, standing immovable in space. A luminous body appears in the distance, little by little you see it approach and increase in size; its immense circumference, which exceeds a hundred thousand leagues, is in rapid rotation, which makes each point on its periphery travel through nine miles a second. The globe itself passes before you, carried through space with a velocity twenty-four times greater than that of a cannon-ball. In such a way Jupiter would appear to you traveling in its orbit. This headlong course would banish it forever to the most remote regions of the visible universe, if it were not subdued and held by the powerful attraction of a globe a thousand times larger than its own—by the sun himself. Not only does astronomy show, by undeniable proofs, the reality of these marvelous movements—not only has she arrived at the knowledge of their invariable constancy, at least during thousands of centuries; but she has found in their very rapidity the cause of the stability of all the celestial bodies.

If there is difficulty in imagining such masses freely circulating in the ether, how much more are we impressed when we consider that these rapid movements are not confined to the planets; and when we look upon the sun with all his retinue as moving in an orbit yet unknown, himself attracted no doubt by a more powerful sun, or by a group of suns! All the stars which by reason of their infinite distances appear immovable, move in different directions; and we shall see later, that if these movements are performed with extreme slowness, the slowness is apparent only. In reality, these are the most rapid celestial movements that we know of.

Thousands of centuries will be necessary before these immense sidereal voyages are accomplished. Their vast periods are to the length of our year what the dimensions of the earth are to the distances of the stars; and, according to the happy expression of Humboldt, they make of the universe an eternal timekeeper. Thus, in the contemplation of celestial phenomena, the idea of infinite duration impresses itself on the mind with the same irresistible power as the idea of the infinity of space.

FOOTNOTES:

Via Lactea. It is also called the Galaxy, from the Greek word for the same thing.

SPACE.—RICHARD A. PROCTOR

Although astronomy tells us in the clearest words of the vast depths of space which surround our earth on all sides, we are not thereby enabled to realize their enormous extension. It is not merely that the unknown depths beyond the range of our most powerful telescopes are inconceivable, but that the parts of space which we can examine are on too large a scale for us to conceive their real dimensions. It is hardly going too far to say that our powers of actual conception are limited to the extent of space over which the eye seems to range in the daytime. Of course, in the daytime, at least in clear weather, there is one direction in which the eyesight ranges over a distance of many millions of miles—namely, where we see the sun. But the sense of sight is not cognizant of that enormous distance, and simply presents the sun to us as a bright disk in the sky, or perhaps rather nearer to us than the sky. Even the distance of the sky itself is underestimated. A portion of the light we receive from the sky on a clear day comes from parts of the atmosphere distant more than thirty or forty miles from us; but the eye does not recognize the fact. The blue sky seems a little further off than the clouds, but not much; the light clouds of summer seem a little, but not much, further off than the heavier clouds of a winter sky; a cloud-covered winter sky seems a little further off than heavy rain-clouds. The actual varieties of distance among clouds of various kinds are not much more clearly discerned than the actual varieties of distance among the heavenly bodies. The estimate formed of the distance of a cloud-covered sky overhead probably amounts to little more than a mile, and it is very doubtful whether the mind presents the remotest depths of a blue sky overhead at more than two miles. Toward the horizon the distance seems greater, and probably on a cloudy day the sky near the horizon is unconsciously regarded as at a distance of about five miles, while blue sky near the horizon may be regarded as lying at a distance of six or seven miles, the arch of a blue sky seeming to be far more deeply curved than that of a cloud-covered sky.

It is to distances such as these that the mind unconsciously refers the celestial bodies. We know that the moon is about 2,000 miles in diameter, but the mind refuses to present her to us as other than a round disk much smaller than those other objects in sight which occupy a much larger portion of the field of vision. The sun can not be conceived to exceed the moon enormously in size, seeing that he appears no larger; and all the multitude of stars are judged by the sight to be mere bright points of light in reality as they appear to be.