Astronomy for Amateurs Part 6

[Ill.u.s.tration: FIG. 25.--The Pleiades.]

Without going thus far, and penetrating into telescopic depths, my readers can get some notion of these star-cl.u.s.ters with the help of a small telescope or opera-gla.s.ses, or even with the unaided eye, by looking at the beautiful group of the Pleiades, already familiar to us on another page, and using it as a test of vision. The little map subjoined (Fig. 25) will be an a.s.sistance in recognizing them, and in estimating their magnitudes, which are in the following order:

Alcyone 3.0.

Electra 4.5.

Atlas 4.6.

Maia 5.0.

Merope 5.5.

Taygeta 5.8.

Pleione 6.3.

Celaeno 6.5.

Asterope 6.8.

Good eyes distinguish the first six, sharp sight detects the three others.

In the times of the ancient Greeks, seven were accounted of equal brilliancy, and the poets related that the seventh star had fled at the time of the Trojan War. Ovid adds that she was mortified at not being embraced by a G.o.d, as were her six sisters. It is probable that only the best sight could then distinguish Pleione, as in our own day. The angular distance from Atlas to Pleione is 5'.

The length of this republic, from Atlas and Pleione to Celaeno, is 4'/23"

of time, or 16' of arc; the breadth, from Merope to Asterope, is 36'.[8]

In the quadrilateral, the length from Alcyone to Electra is 36', and the breadth from Merope to Maia 25'. To us it appears as though, if the Full Moon were placed in front of this group of nine stars, she would cover it entirely, for to the naked eye she appears much larger than all the Pleiades together. But this is not so. She only measures 31', less than half the distance from Atlas to Celaeno; she is hardly broader than the distance from Alcyone to Atlas, and could pa.s.s between Merope and Taygeta without touching either of these stars. This is a perennial and very curious optical illusion. When the Moon pa.s.ses in front of the Pleiades, and occults them successively, it is hard to believe one's eyes. The fact occurred, _e.g._, on July 23, 1897, during a fine occultation observed at the author's laboratory of Juvisy (Fig. 26).

[Ill.u.s.tration: FIG. 26.--Occultation of the Pleiades by the Moon.]

Photography here discovers to us, not 6, 9, 12, 15, or 20 stars, but hundreds and millions.

These are the most brilliant flowers of the celestial garden.

[Ill.u.s.tration: FIG. 27.--Stellar dial of the double star [gamma] of the Virgin.]

We, alas, can but glance at them rapidly. In contemplating them we are transported into immensities both of s.p.a.ce and time, for the stellar periods measured by these distant universes often overpower in their magnitude the rapid years in which our terrestrial days are estimated.

For instance, one of the double stars we spoke of above, [gamma] of the Virgin, sees its two components, translucent diamonds, revolve around their common center of gravity, in one hundred and eighty years. How many events took place in France, let us say, in a single year of this star!--The Regency, Louis XV, Louis XVI, the Revolution, Napoleon, Louis XVIII, Louis Philippe, the Second Republic, Napoleon III, the Franco-German War, the Third Republic.... What revolutions here, during a single year of this radiant pair! (Fig. 27.)

But the pageant of the Heavens is too vast, too overwhelming. We must end our survey.

Our Milky Way, with its millions of stars, represents for us only a portion of the Creation. The illimitable abysses of Infinitude are peopled by other universes as vast, as imposing, as our own, which are renewed in all directions through the depths of s.p.a.ce to endless distance. Where is our little Earth? Where our Solar System? We are fain to fold our wings, and return from the Immense and Infinite to our floating island.

CHAPTER IV

OUR STAR THE SUN

In the incessant agitation of daily life in which we are involved by the thousand superfluous wants of modern "civilization," one is p.r.o.ne to a.s.sume that existence is complete only when it reckons to the good an incalculable number of petty incidents, each more insignificant than the last. Why lose time in thinking or dreaming? We must live at fever heat, must agitate, and be infatuated for inanities, must create imaginary desires and torments.

The thoughtful mind, p.r.o.ne to contemplation and admiration of the beauties of Nature, is ill at ease in this perpetual vortex that swallows everything--satisfaction, in a life that one has not time to relish; love of the beautiful, that one views with indifference; it is a whirlpool that perpetually hides Truth from us, forgotten forever at the bottom of her well.

And why are our lives thus absorbed in merely material interests? To satisfy our pride and vanity! To make ourselves slaves to chimeras! If the Moon were inhabited, and if her denizens could see us plainly enough to note and a.n.a.lyze the details of human existence on the surface of our planet, it would be curious and perhaps a little humiliating for us, to see their statistics. What! we should say, is this the sum of our lives? Is it for this that we struggle, and suffer, and die? Truly it is futile to give ourselves such trouble.

And yet the remedy is simple, within the power of every one; but one does not think of it just because it is too easy, although it has the immense advantage of lifting us out of the miseries of this weary world toward the inexpressible happiness that must always awaken in us with the knowledge of the Truth: we need only open our eyes to see, and to look out. Only--one hardly ever thinks of it, and it is easier to let one's self be blinded by the illusion and false glamor of appearances.

Think what it would be to consecrate an hour each day to voluntary partic.i.p.ation in the harmonious Choir of Nature, to raise one's eyes toward the Heavens, to share the lessons taught by the Pageant of the Universe! But, no: there is no time, no time for the intellectual life, no time to become attached to real interests, no time to pursue them.

Among the objects marshaled for us in the immense spectacle of Nature, nothing without exception has struck the admiration and attention of man as much as the Sun, the G.o.d of Light, the fecundating orb, without which our planet and its life would never have issued from nonent.i.ty, _the visible image of the invisible G.o.d_, as said Cicero, and the poets of antiquity. And yet how many beyond the circle of those likely to read these pages know that this Sun is a star in the Milky Way, and that every star is a sun? How many take any account of the reality and grandeur of the Universe? Inquire, and you will find that the number of people who have any notion, however rudimentary, of its construction, is singularly restricted. Humanity is content to vegetate, much after the fas.h.i.+on of a race of moles.

Henceforward, you will know that you are living in the rays of a star, which, from its proximity, we term a sun. To the inhabitants of other systems of worlds, our splendid Sun is only a more or less brilliant, luminous point, according as the spot from which it is observed is nearer or farther off. But to us its "terrestrial" importance renders it particularly precious; we forget all the sister stars on its account, and even the most ignorant hail it with enthusiasm without exactly knowing what its role in the universe may be, simply because they feel that they depend on it, and that without it life would become extinct on this globe. Yes, it is the beneficent rays of the Sun that shed upon our Earth the floods of light and heat to which Life owes its existence and its perpetual propagation.

Hail, vast Sun! a little star in Infinitude, but for us a colossal and portentous luminary. Hail, divine Benefactor! How should we not adore, when we owe him the glow of the warm and cheery days of summer, the gentle caresses by which his rays touch the undulating ears, and gild them with the touch? The Sun sustains our globe in s.p.a.ce, and keeps it within his rays by the mysteriously powerful and delicate cords of attraction. It is the Sun that we inhale from the embalmed corollas of the flowers that uplift their gracious heads toward his light, and reflect his splendors back to us. It is the Sun that sparkles in the foam of the merry wine; that charms our gaze in those first days of spring, when the home of the human race is adorned with all the charms of verdant and flowering youth. Everywhere we find the Sun; everywhere we recognize his work, extending from the infinitely great to the infinitely little. We bow to his might, and admire his power. When in the sad winter day he disappears behind the snowy eaves, we think his fiery globe will never rise to mitigate the short December days which are alleviated with his languid beams.

April restores him to superb majesty, and our hearts are filled with hope in the illumination of those beauteous, sunny hours.

Our celestial journey carried us far indeed from our own Solar System.

Guided by the penetrating eye of the telescope, we reached such distant creations that we lost sight of our cherished luminary.

But we remember that he burns yonder, in the midst of the pale cosmic cloud we term the Milky Way. Let us approach him, now that we have visited the Isles of Light in the Celestial Ocean; let us traverse the vast plains strewn with the burning gold of the Suns of the Infinite.

We embark upon a ray of light, and glide rapidly to the portals of our Universe. Soon we perceive a tiny speck, scintillating feebly in the depths of s.p.a.ce, and recognize it as our own celestial quarters. This little star s.h.i.+nes like the head of a gold pin, and increases in size as we advance toward it. We traverse a few more trillion miles in our rapid course, and it s.h.i.+nes out like a fine star of the first magnitude. It grows larger and larger. Soon we divine that it is our humble Earth that is s.h.i.+ning before us, and gladly alight upon her. In future we shall not quit our own province of the Celestial Kingdom, but will enter into relations with this solar family, which interests us the more in that it affects us so closely.

[Ill.u.s.tration: FIG. 28.--Comparative sizes of the Sun and Earth.]

The Sun, which is manifested to us as a fine white disk at noon, while it is fiery red in the evening, at its setting, is an immense globe, whose colossal dimensions surpa.s.s those of our terrestrial atom beyond all conceivable proportion.

In diameter, it is, in effect, 108-1/2 times as large as the Earth; that is to say, if our planet be represented by a globe 1 meter in diameter, the Sun would figure as a sphere 108-1/2 meters across. This is shown on the accompanying figure (Fig. 28), which is in exact proportion.

If our world were set down upon the Sun, with all its magnificence, all its wealth, its mountains, its seas, its monuments, and its inhabitants, it would only be an imperceptible speck. It would occupy less s.p.a.ce in the central orb than one grain in a grenade. If the Earth were placed in the center of the Sun, with the Moon still revolving round it at her proper distance of 384,000 kilometers (238,500 miles), only half the solar surface would be covered.

In volume the Sun is 1,280,000 times vaster than our abode, and 324,000 times heavier in ma.s.s. That the giant only appears to us as a small though very brilliant disk, is solely on account of its distance. Its apparent dimensions by no means reveal its majestic proportions to us.

When observed with astronomical instruments, or photographed, we discover that its surface is not smooth, as might be supposed, but granulated, presenting a number of luminous points dispersed over a more somber background. These granulations are somewhat like the pores of a fruit, _e.g._, a fine orange, the color of which recalls the hue of the Sun when it sinks in the evening, and prepares to plunge us into darkness. At times these pores open under the influence of disturbances that arise upon the solar surface, and give birth to a Sun-Spot. For centuries scientists and lay people alike refused to admit the existence of these spots, regarding them as so many blemishes upon the King of the Heavens. Was not the Sun the emblem of inviolable purity? To find any defect in him were to do him grievous injury. Since the orb of day was incorruptible, those who threw doubt on his immaculate splendor were fools and idiots. And so when Scheiner, one of the first who studied the solar spots with the telescope, published the result of his experiments in 1610, no one would believe his statements.

Yet, from the observations of Galileo and other astronomers, it became necessary to accept the evidence, and stranger still to recognize that it is by these very spots that we are enabled to study the physical const.i.tution of the Sun.

They are generally rounded or oval in shape, and exhibit two distinct parts; first, the central portion, which is black, and is called the _nucleus_, or _umbra_; second, a clearer region, half shaded, which has received the name of _penumbra_. These parts are sharply defined in outline; the penumbra is gray, the nucleus looks black in relation to the dazzling brilliancy of the solar surface; but as a matter of fact it radiates a light 2,000 times superior in intensity to that of the full moon.

[Ill.u.s.tration: FIG. 29.--Direct photograph of the Sun.]

Some idea of the aspect of these spots may be obtained from the accompanying reproduction of a photograph of the Sun (taken September 8, 1898, at the author's observatory at Juvisy), and from the detailed drawing of the large spot that broke out some days later (September 13), crossed by a bridge, and furrowed with flames. As a rule, the spots undergo rapid transformations.

[Ill.u.s.tration: FIG. 30.--Telescopic aspect of a Sun-Spot.]

These spots, which appear of insignificant dimensions to the observers on the Earth, are in reality absolutely gigantic. Some that have been measured are ten times as large as the Earth's diameter, _i.e._, 120,000 kilometers (74,500 miles).

Sometimes the spots are so large that they can be seen with the unaided eye (protected with black or dark-blue gla.s.ses). They are not formed instantaneously, but are heralded by a vast commotion on the solar surface, exhibiting, as it were, luminous waves or _faculae_. Out of this agitation arises a little spot, that is usually round, and enlarges progressively to reach a maximum, after which it diminishes, with frequent segmentation and shrinkage. Some are visible only for a few days; others last for months. Some appear, only to be instantly swallowed in the boiling turmoil of the flaming orb. Sometimes, again, white incandescent waves emerge, and seem to throw luminous bridges across the central umbra. As a rule the spots are not very profound.

They are funnel-shaped depressions, inferior in depth to the diameter of the Earth, which, as we have seen, is 108 times smaller than that of the Sun.