Astronomy for Amateurs Part 9

When we contemplate this radiant Venus, it is difficult, even if we can not form any definite idea as to her actual state as regards habitation, to a.s.sume that she must be a dreary desert, and not, on the contrary, to hail in her a celestial land, differing more or less from our own dwelling-place, travailing with her sisters in the accomplishment of the general plan of Nature.

Such are the characteristic features of our celestial neighbor. In quitting her, we reach the Earth, which comes immediately next her in order of distance, 149 million kilometers (93,000,000 miles) from the Sun, but as we shall devote an entire chapter to our own planet, we will not halt at this point, but cross in one step the distance that separates Mars from Venus.

Let us only remark in pa.s.sing, that our planet is the largest of the four spheres adjacent to the Sun. Here are their comparative diameters:

The Earth = 1. In Kilometers. In Miles.

Mercury 0.373 4,750 2,946 Venus 0.999 12,730 7,894 Earth 1.000 12,742 7,926 Mars 0.528 6,728 4,172

It will be seen that Venus is almost identical with the Earth.

MARS

Two hundred and twenty-six millions of kilometers (140,000,000 miles) from the Sun is the planet Mars, gravitating in an orbit exterior to that which the Earth takes annually round the same center.

Unfortunate Mars! What evil fairy presided at his birth? From antiquity, all curses seem to have fallen upon him. He is the G.o.d of war and of carnage, the protector of armies, the inspirer of hatred among the peoples, it is he who pours out the blood of Humanity in international hecatombs. Here, again, as in the case of Mercury and Venus, the appearance has originated the idea. Mars, in fact, burns like a drop of blood in the depths of the firmament, and it is this ruddy color that inspired its name and attributes, just as the dazzling whiteness of Venus made her the G.o.ddess of love and beauty. Why, indeed, should the origins of mythology be sought elsewhere than in astronomy?

While Humanity was attributing to the presumptive influence of Mars the defects inherent in its own terrestrial nature, this world, unwitting of our sorrows, pursued the celestial path marked out for it in s.p.a.ce by destiny.

This planet is, as we have said, the first encountered after the Earth.

Its...o...b..t is very elongated, very eccentric. Mars accomplishes it in a period of 1 year, 321 days, 22 hours, _i.e._, 1 year, 10 months, 21 days, or 687 days. The velocity of its transit is 23 kilometers (14.5 miles) per second; that of the Earth is 30 (19 miles). Our planet, traveling through s.p.a.ce at an average distance of 149 million kilometers (93,000,000 miles) from the central focus, is separated from Mars by an average distance of 76 million kilometers (47,000,000 miles); but as its...o...b..t is equally elliptic and elongated it follows that at certain epochs the two planets approach one another by something less than 60 million kilometers (37,000,000 miles). These are the periods selected for making the best observations upon our neighbor of the ruddy rays.

The oppositions of Mars arrive about every twenty-six months, but the periods of its greatest proximity, when this planet approaches to within 56 million kilometers (34,700,000 miles) of the Earth, occur only every fifteen years.

Mars is then pa.s.sing perihelion, while our world is at aphelion (or greatest distance from the Sun). At such epochs this globe presents to us an apparent diameter 63 times smaller than that of the Moon, _i.e._, a telescope that magnifies 63 times would show him to us of the same magnitude as our satellite viewed with the unaided eye, and an instrument that magnified 630 times would show him ten times larger in diameter.

In dimensions he differs considerably from our world, being almost half the size of the Earth. In diameter he measures only 6,728 kilometers (4,172 miles), and his circ.u.mference is 21,125 kilometers (13,000 miles). His surface is only 29/100 of the terrestrial surface, and his volume only 15/100 of our own.

This difference in volume causes Mars to be an earth in miniature. When we study his aspects, his geography, his meteorology, we seem to see in s.p.a.ce a reduction of our own abode, with certain dissimilarities that excite our curiosity, and make him even more interesting to us.

The Martian world weighs nine times and a half less than our own. If we represent the weight of the Earth by 1,000, that of Mars would be represented by 105. His density is much less than our own; it is only 7/10 that of the Earth. A man weighing 70 kilograms, transported to the adjacent globe, would weigh only 26 kilograms.

The earliest telescopic observations revealed the existence of more or less accentuated markings upon the surface of Mars. The progress of optics, admitting of greater magnifications, exhibited the form of these patches more clearly, while the study of their motions enabled the astronomers to determine with remarkable precision the diurnal rotation of this planet. It occurs in 24 hours, 37 minutes, 23.65 seconds. Day and night are accordingly a little longer on Mars than on the Earth, but the difference is obviously inconsiderable. The year of Mars consists of 668 Martian days. The inclination of the axis of rotation of this globe upon the plane of its...o...b..t is much the same as our own. In consequence, its seasons are a.n.a.logous to ours in intensity, while twice the length, the Martian year being almost equal to two of our years. The intensity of the seasons is indeed more accentuated than upon the Earth, since the orbit of Mars is very elongated. But there, as here, are three quite distinct zones: the torrid, the temperate, and the glacial.

By means of the telescope we can follow the variations of the Martian seasons, especially in what concerns the polar snows, which regularly aggregate during the winter, and melt no less regularly during the heat of the summer. These snows are very easily observed, and stand out clearly with dazzling whiteness. The reader can judge of them by the accompanying figure, which sums up the author's observations during one of the recent oppositions of Mars (1900-1901). The size of the polar cap diminished from 4,680 kilometers to 840. The solstice of the Martian summer was on April 11th. The snows were still melting on July 6th.

Sometimes they disappear almost entirely during the Martian month that corresponds to our month of August, as never happens with our polar ice.

Hence, though this planet is farther away from the Sun than ourselves, it does not appear to be colder, or, at any rate, it is certain that the polar snows are much less thick.

On the other hand, there are hardly ever clouds on Mars; the Martian atmosphere is almost always limpid, and one can say that fine weather is the chronic state of the planet. At times, light fogs or a little vapor will appear in certain regions, but they are soon dissipated, and the sky clears up again.

[Ill.u.s.tration: FIG. 40.--Diminution of the polar snows of Mars during the summer.]

Since the invention of the telescope, a considerable number of drawings have been made, depicting Mars under every aspect, and the agreement between these numerous observations gives us a sufficient acquaintance with the planet to admit of our indicating the characteristic features of its geography, and of drawing out _areographic_ maps (_Ares_, Mars).

Its appearance can be judged of from the two drawings here reproduced, as made (February, 1901) at the Observatory of Juvisy, and from the general chart drawn from the total sum of observations (Figs. 41, 42 and 43).

It will be seen at the first glance that the geography of Mars is very different from that of our own globe: while three-quarters of the Earth are covered with the liquid element, Mars seems to be more evenly divided, and must indeed have rather more land than water. We find no immense oceans surrounding the continents, and separating them like islands; on the contrary, the seas are reduced to long gulfs compressed between the sh.o.r.es, like the Mediterranean for example, nor is it even certain that these gray spots do all represent true seas. It has been agreed to term _sea_ the parts that are lightly tinged with green, and to give the name of _continent_ to the spots colored yellow. That is the hue of the Martian soil, due either to the soil itself, which would resemble that of the Sahara, or, to take a less arid region, that seen on the line between Ma.r.s.eilles and Nice, in the vicinity of the Esterels; or perhaps to some peculiar vegetation. During ascents in a balloon, the author has often remarked that the hue of the ripe corn, with the Sun s.h.i.+ning on it, is precisely that presented to us by the continents of Mars in the best hours for observation.

[Ill.u.s.tration: FIG. 41.--Telescopic aspect of the planet Mars (Feb., 1901).]

As to the "seas," it is pretty certain that there must be water, or some kind of liquid, deriving above all from the melting of the polar snows in spring and summer; but it may possibly be in conjunction with some vegetation, aquatic plants, or perhaps vast meadows, which appear to us from here to be the more considerable in proportion as the water that nourishes them has been more abundant.

[Ill.u.s.tration: FIG. 42.--Telescopic aspect of the planet Mars (Feb., 1901).]

Mars, like our globe, is surrounded with a protective atmosphere, which retains the rays of the Sun, and must preserve a medium temperature favorable to the conservation of life upon the surface of the planet.

But the circulation of the water, so important to terrestrial life, whether animal or vegetable, which is effected upon our planet by the evaporation of the seas, clouds, winds, rains, wells, rivers and streams, comes about quite differently on Mars; for, as was remarked above, it is rarely that any clouds are observed there. Instead of being vertical, as here, this circulation is horizontal: the water coming from the source of the polar snows finds its way into the ca.n.a.ls and seas, and returns to be condensed at the poles by a light drift of invisible vapors directed from the equator to the poles. There is never any rain.

We have spoken of _ca.n.a.ls_. One of the great puzzles of the Martian world is incontestably the appearance of straight lines that furrow its surface in all directions, and seem to connect the seas. M.

Schiaparelli, the distinguished Director of the Observatory of Milan, who discovered them in 1877, called them ca.n.a.ls, without, however, postulating anything as to their real nature. Are they indeed ca.n.a.ls?

These straight lines, measuring sometimes 600 kilometers (372 miles) in length, and more than 100 kilometers (62 miles) in breadth, have much the same hue as the seas on which they open. For a quarter of a century they have been surveyed by the greater number of our observers. But it must be confessed that, even with the best instruments, we only approach Mars at a distance of 60,000 kilometers (37,200 miles), which is still a little far off, and we may be sure that we do not distinguish the true details of the surface.[11] These details at the limits of visibility produce the appearance of ca.n.a.ls to our eyes. They may possibly be lines of lakes, or oases. The future will no doubt clear up this mystery for us.

[Ill.u.s.tration: FIG. 43.--Chart of Mars.]

As to the inhabitants of Mars, this world is in a situation as favorable as our Earth for habitation, and it would be difficult to discover any reason for perpetual sterility there. It appears to us, on the contrary, by its rapid and frequent variations of aspect, to be a very living world. Its atmosphere, which is always clear, has not the density of our own, and resembles that of the highest mountains. The conditions of existence there vary from ours, and appear to be more delicate, more ethereal.

There as here, day succeeds to night, spring softens the rigors of winter; the seasons unfold, less disparate than our own, of which we have such frequent reason to complain. The sky is perpetually clear.

There are never tempests, hurricanes, nor cyclones, the wind never gets up any force there, on account of the rarity of the atmosphere, and the low intensity of weight.

Differing from ours, this world may well be a more congenial habitation. It is more ancient than the Earth, smaller, less ma.s.sive. It has run more quickly through the phases of its evolution. Its astral life is more advanced, and its Humanity should be superior to our own, just as our successors a million years hence, for example, will be less coa.r.s.e and barbarous than we are at present: the law of progress governs all the worlds, and, moreover, the physical const.i.tution of the planet Mars is less dense than our own.

There is no need to despair of entering some day into communication with these unknown beings. The luminous points that have been observed are no signals, but high summits or light clouds illuminated by the rising or setting sun. But the idea of communication with them in the future is no more audacious and no less scientific than the invention of spectral a.n.a.lysis, X-rays, or wireless telegraphy.

We may suppose that the study of astronomy is further advanced in Mars than on the Earth, because humanity itself has advanced further, and because the starry sky is far finer there, far easier to study, owing to the limpidity of its pure, clear atmosphere.

Two small moons (hardly larger than the city of Paris) revolve rapidly round Mars; they are called Phobos and Deimos. The former, at a distance of 6,000 kilometers (3,730 miles) from the surface, accomplishes its revolution rapidly, in seven hours, thirty-nine minutes, and thus makes the entire circle of the Heavens three times a day. The second gravitates at 20,000 kilometers (12,400 miles), and turns round its center of attraction in thirty hours and eighteen minutes. These two satellites were discovered by Mr. Hall, at the University of Was.h.i.+ngton, in the month of August, 1877.

Among the finest and most interesting of the celestial phenomena admired by the Martians, at certain epochs of the year,--now at night when the Sun has plunged into his fiery bed, now in the morning, a little before the aurora,--is a magnificent star of first magnitude, never far removed from the orb of day, which presents to them the same aspects as does Venus to ourselves. This splendid orb, which has doubtless received the most flattering names from those who contemplate it, this radiant star of a beautiful greenish blue, courses in s.p.a.ce accompanied by a little satellite, sparkling like some splendid diamond, after sunset, in the clear sky of Mars. This superb orb is the Earth, and the little star accompanying it is the Moon.

[Ill.u.s.tration: FIG. 44.--The Earth viewed from Mars.]

Yes, to the Martians our Earth is a star of the morning and evening; doubtless they have determined her phases. Many a vow, and many a hope must have been wafted toward her, more than one broken heart must have permitted its unrealized dreams to wander forth to our planet as to an abode of happiness where all who have suffered in their native world might find a haven. But our planet, alas! is not as perfect as they imagine.

We must not dally upon Mars, but hasten our celestial excursion toward Jupiter.

CHAPTER VI

THE PLANETS

_B._--JUPITER, SATURN, URa.n.u.s, NEPTUNE.

Before we attack the giant world of our system, we must halt for a few moments upon the minor planets which circulate between the orbit of Mars and that of Jupiter. These minute asters, little worlds, the largest of which measures scarcely more than 100 kilometers (62 miles) in diameter, are fragments of cosmic matter that once belonged to a vast ring, formed at the time when the solar system was only an immense nebula; and which, instead of condensing into a single globe coursing between Mars and Jupiter, split up into a considerable quant.i.ty of particles const.i.tuting at the present time the curious and highly interesting Republic of the Asteroids.

These lilliputian worlds at first received the names of the more celebrated of the minor mythological divinities--Ceres, Pallas, Juno, Vesta, etc., but as they rapidly increased in number, it was found necessary to call them by modern, terrestrial names, and more than one daughter of Eve, the Egeria of some astronomer, now has her name inscribed in the Heavens. The first minor planet was discovered on the first day of the nineteenth century, January 1, 1801, by Piazzi, astronomer at Palermo. While he was observing the small stars in the constellation of the Bull beneath the clear Sicilian skies, this famous astronomer noticed one that he had never seen before.