Astronomy for Amateurs Part 12

What marvels have been reviewed by our dazzled eyes since the outset of these discussions! We first surveyed the magnificent host of stars that people the vast firmament of Heaven; next we admired and wondered at suns very differently const.i.tuted from our own; then returning from the depths of s.p.a.ce, crossing at a bound the abyss that separates us from these mysterious luminaries, the distant torches of our somber night, terrible suns of infinity, we landed on our own beloved orb, the superb and brilliant day-star. Thence we visited his celestial family, his system, in which our Earth is a floating island. But the journey would be incomplete if we omitted certain more or less vagabond orbs, that occasionally approach the Sun and Earth, some of which may even collide with us upon their celestial path. These are in the first place the comets, then the shooting stars, the fire-b.a.l.l.s, and meteorites.

Glittering, swift-footed heralds of Immensity, these comets with golden wings glide lightly through s.p.a.ce, shedding a momentary illumination by their presence. Whence come they? Whither are they bound?

What problems they propound to us, when, as in some beautiful display of pyrotechnics, the arch of Heaven is illuminated with their fantastic light!

But first of all--what is a Comet?

If instead of living in these days of the telescope, of spectrum a.n.a.lysis, and of astral photography, we were anterior to Galileo, and to the liberation of the human spirit by Astronomy, we should reply that the comet is an object of terror, a dangerous menace that appears to mortals in the purity of the immaculate Heavens, to announce the most fatal misfortunes to the inhabitants of our planet. Is a comet visible in the Heavens? The reigning prince may make his testament and prepare to die. Another apparition in the firmament bodes war, famine, the advent of grievous pestilence. The astrologers had an open field, and their fertile imagination might hazard every possible conjecture, seeing that misfortunes, great or small, are not altogether rare in this sublunar world.

How many intellects, and those not the most vulgar, from antiquity to the middle of the last century cursed the apparition of these hirsute stars, which brought desolation to the heart of man, and poured their fatal effluvia upon the head of poor Humanity. The history of the superst.i.tions and fears that they inspired of old would furnish matter for the most thrilling of romances. But, on the other hand, the volume would be little flattering to the common-sense of our ancestors. Despite the respect we owe our forefathers, let us recall for a moment the prejudices attaching to the most famous comets whose pa.s.sage, as observed from the Earth, has been preserved to us in history.

[Ill.u.s.tration: FIG. 49.--Great Comet of 1858.]

Without going back to the Deluge, we note that the Romans established a relation between the Great Comet of 43 B.C. and the death of Caesar, who had been a.s.sa.s.sinated a few months previously. It was, they a.s.serted, the soul of their great Captain, transported to Heaven to reign in the empyrean after ruling here below. Were not the Emperors Lords of both Earth and Heaven?

We must in justice recognize that certain more independent spirits emanc.i.p.ated themselves from these superst.i.tions, and we may cite the reply of Vespasian to his friends, who were alarmed at the evil presage of a flaming comet: "Fear nothing," he said, "this bearded star concerns me not; rather should it threaten my neighbor the King of the Parthians, since he is hairy and I am bald."

In the year 837 one of these mysterious visitants appeared in the Heavens. It was in the reign of Lewis the Debonair. Directly the King perceived the comet, he sent for an astrologer, and asked what he was to conclude from the apparition. As the answers were unsatisfactory he tried to avert the augury by prayers to Heaven, by ordaining a general fast to all his Court, and by building churches. Notwithstanding, he died three years later, and the historians profited by this slender coincidence to set up a correlation between the fatal star and the death of the Sovereign. This comet, famous in history, is no other than that of Halley, in one of its appearances.

This comet returned to explore the realms near the Sun in 1066, at the moment when William of Normandy was undertaking the Conquest of England, and was misguided enough to go across and reign in London, instead of staying at home and annexing England, thus by his action founding the everlasting rivalry between France and this island. A beneficial influence was attributed to the comet in the Battle of Hastings.

A few centuries later it again came into sight from the Earth, in 1456, three years after the capture of Constantinople by the Turks. Feeling ran high in Europe, and this celestial omen was taken for a proof of the anger of the Almighty. The moment was decisive; the Christians had to be rescued from a struggle in which they were being worsted. At this conjuncture, Pope Calixtus resuscitated a prayer that had fallen into disuse, the _Angelus_; and ordered that the bells of the churches should be rung each day at noon, that the Faithful might join at the same hour in prayer against the Turks and the Comet. This custom has lasted down to our own day.

Again, to the comet of 1500 was attributed the tempest that caused the death of Bartholomew Diaz, a celebrated Portuguese navigator, who discovered the Cape of Good Hope.

In 1528 a bearded star of terrific aspect alarmed the world, and the more serious spirits were influenced by this menacing comet, which burned in the Heavens like "a great and gory sword." In a chapter on Celestial Monsters the celebrated surgeon Ambroise Pare describes this awful phenomenon in terms anything but seductive, or rea.s.suring, showing us the menacing sword surrounded by the heads it had cut off (Fig. 50).

[Ill.u.s.tration: FIG. 50.--What our Ancestors saw in a Comet.

_After Ambroise Pare (1528)._]

[Ill.u.s.tration: FIG. 51.--Prodigies seen in the Heavens by our Forefathers.]

Omens of battle, 1547.

Deer and warriors, July 19, 1550.

Cavalry, and a b.l.o.o.d.y branch crossing the sun, June 11, 1554.]

Our fathers saw many other prodigies in the skies; their descendants, less credulous, can study the facsimile reproduced in Fig. 51, of the drawings published in the year 1557 by Conrad Lycosthenes in his curious Book of Prodigies.

So, too, it is a.s.serted that Charles V renounced the jurisdiction of his Estates, which were so vast that "the Sun never slept upon them,"

because he was terrified by the comet of 1556 which burned in the skies with an alarming brilliancy, into pa.s.sing the rest of his days in prayer and devotion.

It is certain that comets often exhibit very strange characteristics, but the imagination that sees in them such dramatic figures must indeed be lively. In the Middle Ages and the Renaissance these were swords of fire, b.l.o.o.d.y crosses, flaming daggers, etc., all horrible objects ready to destroy our poor human race!

At the time of the Romans, Pliny made some curious distinctions between them: "The Bearded Ones let loose their hair like a majestic beard; the Javelin darts forth like an arrow; if the tail is shorter and ends in a point, it is called the Sword; this is the palest of all the Comets; it s.h.i.+nes like a sword, without rays; the Plate or Disk is named in conformity with its figure; its color is amber, the Barrel is actually shaped like a barrel, as it might be in smoke, with light streaming through it; the Horn imitates the figure of a horn erected in the sky, and the Lamp that of a burning flame; the Equine represents a horse's mane, shaken violently with a circular motion. There are bristled comets; these resemble the skins of beasts with the fur on them, and are surrounded by a nebulosity. Lastly, the tails of certain comets have been seen to menace the sky in the form of a lance."

These hairy orbs that appear in all directions, and whose trajectories are sometimes actually perpendicular to the plane of the ecliptic, appear to obey no regular law. Even in the seventeenth century the perspicacious Kepler had not divined their true character, seeing in them, like most of his contemporaries, emanations from the earth, a sort of vapor, losing itself in s.p.a.ce. These erratic orbs could not be a.s.similated with the other members of our grand solar family where, generally speaking, everything goes on in regular order.

And even in our own times, have we not seen the people terrified at the sight of a flaming comet? Has not the end of the world by the agency of comets been often enough predicted? These predictions are so to speak periodic; they crop up each time that the return of these cosmical formations is announced by the astronomers, and always meet with a certain number of timid souls who are troubled as to our destinies.

To-day we know that these wanderers are subject to the general laws that govern the universe. The great Newton announced that, like the planets, they were obedient to universal attraction; that they must follow an extremely elongated curve, and return periodically to the focus of the ellipse. From the basis of these data Halley calculated the progress of the comet of 1682, and ascertained that its motions presented such similarity with the apparitions of 1531 and 1607, that he believed himself justified in identifying them and in announcing its return about the year 1759. Faithful to the call made upon it, irresistibly attracted by the Orb of Day, the comet, at first pale, then ardent and incandescent, returned at the date a.s.signed to it by calculation, three years after the death of the ill.u.s.trious astronomer.

s.h.i.+ning upon his grave it bore witness to the might of human thought, able to s.n.a.t.c.h the profoundest secrets from the Heavens!

This fine comet returns every seventy-six years, to be visible from the Earth, and has already been seen twenty-four times by the astonished eyes of man. It appears, however, to be diminis.h.i.+ng in magnitude. Its last appearance was in 1835, and we shall see it again in 1910, a little sooner than its average period, the attraction of Jupiter having this time slightly accelerated its course, while in 1759 it r.e.t.a.r.ded it.

The comets thus follow a very elongated orbit, either elliptic, turning round the Sun, or parabolic, das.h.i.+ng out into s.p.a.ce. In the first case, they are periodic (Fig. 52), and their return can be calculated. In the second they surprise us unannounced, and return to the abysses of eternity to reappear no more.

[Ill.u.s.tration: FIG. 52.--The orbit of a Periodic Comet.]

Their speed is even greater than that of the planets, it is equivalent to this, multiplied by the square root of 2, that is to say by 1.414.

Thus at the distance of the Earth from the Sun this velocity = 29,500 meters (18 miles) per second, multiplied by the above number, that is, 41,700 meters (over 25 miles). At the distance of Mercury it = 47 1.414 or 66,400 meters (over 40 miles) per second.

Among the numerous comets observed, we do not as yet know more than some twenty of which the orbit has been determined. Periodicity in these bearded orbs is thus exceptional, if we think of the innumerable mult.i.tude of comets that circle through the Heavens. Kepler did not exaggerate when he said "there are as many comets in the skies as there are fishes in the sea." These scouts of the sidereal world const.i.tute a regular army, and if we are only acquainted with the dazzling generals clad in gold, it is because the more modest privates can only be detected in the telescope. Long before the invention of the latter, these wanderers in the firmament roamed through s.p.a.ce as in our own day, but they defied the human eye, too weak to detect them. Then they were regarded as rare and terrible objects that no one dared to contemplate.

To-day they may be counted by hundreds. They have lost in prestige and in originality; but science is the gainer, since she has thus endowed the solar system with new members. No year pa.s.ses without the announcement of three or four new arrivals. But the fine apparitions that attract general attention by their splendor are rare enough.

These eccentric visitors do not resemble the planets, for they have no opaque body like the Earth, Venus, Mars, or any of the rest. They are transparent nebulosities, of extreme lightness, without ma.s.s nor density. We have just photographed the comet of the moment, July, 1903: the smallest stars are visible through its tail, and even through the nucleus.

They arrive in every direction from the depths of s.p.a.ce, as though to reanimate themselves in the burning, luminous, electric solar center.

Attracted by some potent charm toward this dazzling focus, they come inquisitive and ardent, to warm themselves at its furnace. At first pale and feeble, they are born again when the Sun caresses them with his fervid heat. Their motions accelerate, they haste to plunge wholly into the radiant light. At length they burst out luminous and superb, when the day-star penetrates them with his burning splendor, illuminates them with a marvelous radiance, and crowns them with glory. But the Sun is generous. Having showered benefits upon these gorgeous celestial b.u.t.terflies that flutter round him as round some altar of the G.o.ds, he grants them liberty to visit other heavens, to seek fresh universes....

The original parabola is converted into an ellipse, if the imprudent adventurer in returning to the Sun pa.s.ses near some great planet, such as Jupiter, Saturn, Ura.n.u.s, or Neptune, and suffers its attraction. It is then imprisoned by our system, and can no longer escape from it.

After reenforcement at the solar focus, it must return to the identical point at which it felt the first pangs of a new destiny. Henceforward, it belongs to our celestial family, and circles in a closed curve.

Otherwise, it is free to continue its rapid course toward other suns and other systems.

As a rule, the telescope shows three distinct parts in a comet. There is first the more brilliant central point, or _nucleus_, surrounded by a nebulosity called the _hair_, or _brush_, and prolonged in a luminous appendix stretching out into the _tail_. The _head_ of the comet is the brush and the nucleus combined.

[Ill.u.s.tration: FIG. 53.--The tails of Comets are opposed to the Sun.]

It is usually supposed that the tail of a comet follows it throughout the course of its peregrinations. Nothing of the kind. The appendix may even precede the nucleus; it is always opposite the Sun,--that is to say, it is situated on the prolongation of a straight line, starting from the Sun, and pa.s.sing through the nucleus (Fig. 53). The tail does not exist, so long as the comet is at a distance from the orb of day; but in approaching the Sun, the nebulosity is heated and dilates, giving birth to those mysterious tails and fantastic streamers whose dimensions vary considerably for each comet. The dilations and transformations undergone by the tail suggest that they may be due to a repulsive force emanating from the Sun, an electric charge transmitted doubtless through the ether. It is as though Phoebus blew upon them with unprecedented force.

Telescopic comets are usually devoid of tail, even when they reach the vicinity of the Sun. They appear as pale nebulosities, rounded or oval, more condensed toward the center, without, however, showing any distinct nucleus. These stars are only visible for a minute fraction of their course, when they reach a point not far from the Sun and the terrestrial orbit.

The finest comets of the last century were those of 1811, 1843, 1858, 1861, 1874, 1880, 1881, and 1882. The Great Comet of 1811, after spreading terror over certain peoples, notably in Russia, became the providence of the vine-growers. As the wine was particularly good and abundant that year, the peasants attributed this happy result to the influence of the celestial visitant.

In 1843 one of these strange messengers from the Infinite appeared in our Heavens. It was so brilliant that it was visible in full daylight on February 28th, alongside of the Sun. This splendid comet was accompanied by a marvelous rectilinear tail measuring 300,000,000 kilometers (186,000,000 miles) in length, and its flight was so rapid that it turned the solar hemisphere at perihelion in two hours, representing a speed of 550 kilometers (342 miles) a second.

But the most curious fact is that this radiant apparition pa.s.sed so near the Sun that it must have traversed its flames, and yet emerged from them safe and sound.