Recreations in Astronomy Part 9

Very likely, since one or two have done so within a recent period.

What will be the effect? That depends on circ.u.mstances. There is good reason to suppose we pa.s.sed through the tail of a comet in 1861, and the only [Page 134] observable effect was a peculiar phosph.o.r.escent mist. If the comet were composed of small meteoric ma.s.ses a brilliant shower would be the result. But if we fairly encountered a nucleus of any considerable ma.s.s and solidity, the result would be far more serious. The ma.s.s of Donati's comet has been estimated by M. Faye to be 1/20000 of that of the earth. If this amount of matter were dense as water, it would make a globe five hundred miles in diameter; and if as dense as Professor Peirce proved the nucleus of this comet to be, its impact with the earth would develop heat enough to melt and vaporize the hardest rocks.

Happily there is little fear of this: as Professor Newcomb says, "So small is the earth in comparison with celestial s.p.a.ce, that if one were to shut his eyes and fire at random in the air, the chance of bringing down a bird would be better than that of a comet of any kind striking the earth." Besides, we are not living under a government of chance, but under that of an Almighty Father, who upholdeth all things by the word of his power; and no world can come to ruin till he sees that it is best.

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VIII.

THE PLANETS AS INDIVIDUALS.

"Through faith we understand that the worlds [plural] were framed by the word of G.o.d, so that things which were seen were not made of things which do appear."--_Heb._ xi. 3.

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"O rich and various man! Thou palace of sight and sound, carrying in thy senses the morning, and the night, and the unfathomable galaxy; in thy brain the geometry of the city of G.o.d; in thy heart the power of love, and the realms of right and wrong. An individual man is a fruit which it costs all the foregoing ages to form and ripen. He is strong, not to do but to live; not in his arms, but in his heart; not as an agent, but as a fact."--EMERSON.

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VII.

_THE PLANETS AS INDIVIDUALS._

How many bodies there may be revolving about the sun we have no means to determine or arithmetic to express. When the new star of the American Republic appeared, there were but six planets discovered. Since then three regions of the solar system have been explored with wonderful success. The outlying realms beyond Saturn yielded the planet Ura.n.u.s in 1781, and Neptune in 1846. The middle region between Jupiter and Mars yielded the little planetoid Ceres in 1801, Pallas in 1802, and one hundred and ninety others since.

The inner region between Mercury and the sun is of necessity full of small meteoric bodies; the question is, are there any bodies large enough to be seen?

The same great genius of Leverrier that gave us Neptune from the observed perturbations of Ura.n.u.s, pointed out perturbations in Mercury that necessitated either a planet or a group of planetoids between Mercury and the sun. Theoretical astronomers, aided by the fact that no planet had certainly been seen, and that all a.s.serted discoveries of one had been by inexperienced observers, inclined to the belief in a group, or that the disturbance was caused by the matter reflecting the zodiacal light.

When the total eclipse of the sun occurred in 1878, [Page 138]

astronomers were determined that the question of the existence of an intra-mercurial planet should be settled. Maps of all the stars in the region of the sun were carefully studied, sections of the sky about the sun were a.s.signed to different observers, who should attend to nothing but to look for a possible planet. It is now conceded that Professor Watson, of Ann Arbor, actually saw the sought-for body.

VULCAN.

The G.o.d of fire; its sign [Symbol], his hammer.

DISTANCE FROM THE SUN, 13,000,000 MILES. ORBITAL REVOLUTION, ABOUT 20 DAYS.

MERCURY.

The swift messenger of the G.o.ds; sign [Symbol], his caduceus.

DISTANCE FROM THE SUN, 35,750,000 MILES. DIAMETER, 2992 MILES.

ORBITAL REVOLUTION, 87.97 DAYS. ORBITAL VELOCITY, 1773 MILES PER MINUTE. AXIAL REVOLUTION, 24H. 5M.

Mercury s.h.i.+nes with a white light nearly as bright as Sirius; is always near the horizon. When nearly between us and the sun, as at D (Fig. 46, p. 113), its illuminated side nearly opposite to us, we, looking from E, see only a thin crescent of its light.

When it is at its greatest angular distance from the sun, as A or C, we see it illuminated like the half-moon. When it is beyond the sun, as at E, we see its whole illuminated face like the full-moon.

The variation of its apparent size from the varying distance is very striking. At its extreme distance from the earth it subtends an angle of only five seconds; nearest to us, an angle of twelve seconds. Its distance from the earth varies nearly as one to three, and its apparent size in the inverse ratio.

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When Mercury comes between the earth and the sun, near the line where the planes of their orbits cut each other by reason of their inclination, the dark body of Mercury will be seen on the bright surface of the sun. This is called a transit. If it goes across the centre of the sun it may consume eight hours. It goes 100,000 miles an hour, and has 860,000 miles of disk to cross. The transit of 1818 occupied seven and a half hours. The transits for the remainder of the century will occur:

November 7th 1881 November 10th 1894 May 9th 1891 November 4th 1901

VENUS.

G.o.ddess of beauty; its sign [Symbol], a mirror.

DISTANCE FROM THE SUN, 66,750,000 MILES. DIAMETER, 7660 MILES.

ORBITAL VELOCITY, 1296 MILES PER MINUTE. AXIAL REVOLUTION, 23H.

21M. ORBITAL REVOLUTION, 224.7 DAYS.

This brilliant planet is often visible in the daytime. I was once delighted by seeing Venus looking down, a little after mid-day through the open s.p.a.ce in the dome of the Pantheon at Rome. It has never since seemed to me as if the home of all the G.o.ds was deserted. Phoebus, Diana, Venus and the rest, thronged through that open upper door at noon of night or day. Arago relates that Bonaparte, upon repairing to Luxemburg when the Directory was about to give him a _fete_, was much surprised at seeing the mult.i.tude paying more attention to the heavens above the palace than to him or his brilliant staff. Upon inquiry, he learned that these curious persons were observing with astonishment a star which they supposed to be that of the conqueror of Italy. The emperor himself was not indifferent when [Page 140] his piercing eye caught the clear l.u.s.tre of Venus smiling upon him at mid-day.

This unusual brightness occurs when Venus is about five weeks before or after her inferior conjunction, and also nearest overhead by being north of the sun. This last circ.u.mstance occurs once in eight years, and came on February 16th, 1878.

Venus may be as near the earth as 22,000,000 miles, and as far away as 160,000,000. This variation of its distances from the earth is obviously much greater than that of Mercury, and its consequent apparent size much more changeable. Its greatest and least apparent sizes are as ten and sixty-five (Fig. 53).

[Ill.u.s.tration: Fig. 53.--Phases of Venus, and Varions Apparent Dimensions.]

When Copernicus announced the true theory of the solar system, he said that if the inferior planets could be clearly seen they would show phases like the moon. When Galileo turned the little telescope he had made on Venus, he confirmed the prophecy of Copernicus.

Desiring to take time for more extended observation, and still be able to a.s.sert the priority of his discovery, he published the following anagram, in which his discovery was contained:

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"Haec immatura a me jam frustra leguntur o. y."

(These unripe things are now vainly gathered by me.)

He first saw Venus as gibbous; a few months revealed it as crescent, and then he transposed his anagram into:

"Cynthiae figuras aemulatur mater amorum."

(The mother of loves imitates the phases of Cynthia.)

Many things that were once supposed to be known concerning Venus are not confirmed by later and better observations. Venus is surrounded by an atmosphere so dense with clouds that it is conceded that her time of rotation and the inclination of her axis cannot be determined. She revealed one of the grandest secrets of the universe to the first seeker; showed her highest beauty to her first ardent lover, and has veiled herself from the prying eyes of later comers.

Florence has built a kind of shrine for the telescope of Galileo.

By it he discovered the phases of Venus, the spots on the sun, the mountains of the moon, the satellites of Jupiter, and some irregularities of shape in Saturn, caused by its rings. Galileo subsequently became blind, but he had used his eyes to the best purpose of any man in his generation.

THE EARTH.

Its sign [Symbol].

DISTANCE FROM THE SUN, 92,500,000 MILES. DIAMETER, POLAR, 7899 MILES; EQUATORIAL, 7925-1/2 MILES. AXIAL REVOLUTION, 23H. 56M.

4.09S.; ORBITAL, 365.86. ORBITAL VELOCITY PER MINUTE, 1152.8 MILES.