THE PLANETS-MARS, VESTA, JUPITER. "And was the ransom paid? it was: and paid A midnight nature shuddered to behold; A midnight new! a dread eclipse (without Which bow'd His blessed head?" 123 Having spent so much time in considering our own habitation THE EARTH, and its Moon; let us now pass on and see what is the next planet in the heavens ;—it is Mars. Mars, which is so named after the heathen god of war, because its red colour gave rise to the idea of bloodshed, is fifty millions of miles further from the sun than the earth. This red hue is supposed to be caused by either an actual redness of the substance of the planet, or owing to the presence of a dark foggy atmosphere. Mars is about half as large as the earth. The year of this planet is nearly twice as long as our own, and his day about half an hour longer than ours. If we could see our earth from the surface of Mars, it would look just as Venus does to us now. Vesta, Juno, Ceres, and Pallas, are at nearly the same distances from the sun, and are very small. Vesta's year is equal to nearly four of ours; Juno's to rather more than four years; Ceres to nearly five years; and Pallas about five years. Jupiter is the largest planet of our system, its diameter being eleven times greater than the earth's, and is next in brilliancy to Venus; at times it even surpasses Venus in brightness. The bulk of Jupiter is thirteen hundred times greater than that of the earth; but although it is so large, it is far less solid than our earth, and his weight (if we could place both in a great pair of scales) would be found not more than three hundred and fifty times more than the earth's. Our year would make just one of Jupiter's months, for Jupiter is twelve of our years going round the sun. The discovery of the moons of Jupiter, by Galileo, was one of the first fruits of the invention of the telescope. Jupiter has four moons attendant on him, which can be seen with a good common telescope; the knowledge of the motions of these is very valuable. The times of their eclipses, as seen at Greenwich, are marked in the Nautical tables, and the time of the same eclipses being noted in another part of the globe, the difference of time is the difference of longitude : of course this cannot be done at sea. The discovery of these satellites and their eclipses also determined the important astronomical fact, that light was not communicated instantaneously, but that it occupied TIME in coming from a luminous body to the eye.* Saturn is still more remote from the sun than Jupiter. Saturn has seven moons, and is also encircled with a brilliant broad ring, sometimes exceeding in brightness the planet itself; Saturn is nearly as large as Jupiter, but its want of solidity is very remarkable. It has been calculated that it is not heavier than a ball of the same bulk made of deal or other light wood. Saturn's bright ring is a solid substance, for it casts a shadow from the sun on the planet. It is about twenty-nine and a half years travelling round the sun. The satellites, or moons, of Saturn, are estimated to be as large as the planet Mars. Uranus, or Georgium Sidus. This used to be considered the last of the planets, and was thought to be placed in the utmost bounds of the solar system; another planet has, however, lately been discovered, of which I will speak directly. Uranus completes its vast orbit in about eighty-four of our years. Its bulk is about equal to eighty earths. Le Verrier's Planet, as it is at present called, was discovered in September, 1846. Little or nothing is yet known about this Roemer, a Danish astronomer, found that the eclipses of Jupiter's Satellites happened about sixteen minutes and a quarter earlier when the Earth was in one part of her orbit, than when she was in the opposite part; and the difference of space being one hundred and ninety millions of miles, the light must travel over this distance in sixteen minutes and a quarter, at the prodigious velocity of a hundred and ninety-three thousand miles in a second.Exercises in Astronomy by the Rev. G. T. Hall. heavenly body, but the circumstances under which it has been discovered are so extraordinary, that I am sure a reference to them will interest you. Astronomers had found that the last-mentioned planet, Uranus, moved irregularly; it seemed to be diverted from its exact course by the agency of some unknown body; and Le Verrier, a Frenchman, was led to calculate how much was this movement, and how large a body it must be to produce it, and how far from Uranus such a body ought to be to affect it as had been observed; and he arrived at the conclusion by mere calculation, that there must be another planet beyond Uranus, and he actually pointed out where it would be found. It was found just where he affirmed it must be! A COMET. THE COMETS. Ere we leave the solar system, to pass into the regions of the stars, we must not omit to consider this singular order of heavenly bodies. The word Comet is derived from the Greek word for hair, and probably the ancients thus applied the word on account of the luminous tail that almost always accompanies them. Though irregular in their movements, yet the return of some of the Comets has been predicted with great accuracy. They are supposed to be of inconsiderable size. The number of the Comets which come within the range of the earth's orbit is estimated at about fourteen hundred. The return of most of these cannot be predicted. Some of them have been observed however with accuracy, and their time of revolution is known. THE HEAVEN OF THE FIXED STARS. Leaving the solar system, one is lost in amazement in passing on into the boundless regions of the apparently motionless stars, all shining in unborrowed lustre; the thought of the Psalmist irresistibly recurs to the mind, "When I consider thy heavens, the work of thy fingers, the moon and the stars, which thou hast ordained; what is man, that thou art mindful of him? and the son of man, that thou visitest him?" (Ps. viii. 3, 4.) And again, how sublime is that appeal to Job, when the Lord, evidently in direct reference to the starry heavens, says,* "Canst thou bind the sweet influences of the Pleiades, or loose the bands of Orion? Canst thou bring forth Mazzaroth in his season? or canst thou guide Arcturus with his sons? Knowest thou the ordinances of heaven? canst thou set the dominion thereof in the earth?" (Job xxxviii. 31-33.) Yes, beloved children, God WALKETH in this circuit of the heaven, (Job xxii. 14,) and all these orbs of light move at his direction; he has appointed them "for times, and for signs, and for seasons." In the absence of the moon, THE STAR-LIGHT OF NIGHT" is most cheering; and in an astronomical point of view, the knowledge of the stars is very valuable; night after night have I at sea beguiled the time in watching this or that fixed star coming to its meridian, and by taking its altitude, ascertained the latitude of the ship: of course these observations, from the obscurity of the horizon, cannot be so accurate as those taken from the sun; but if the sun has not been seen for many days, then they become very valuable; the polar star, with some slight variations allowed, may be thus taken any hour of the night when the sky is clear. The distance of the fixed stars from us is beyond our calculation it may be thus illustrated:-"If we look down a straight : *Again, how striking is that reference to the constellations in Job ix. 1-10. See also Amos v. 8. THE SIGNS OF THE ZODIAC. 127 road, the pathway on each side seems to unite in the distance; and at this point, if there were two trees, one on each side, they would appear one; but as we walk along the road, the trees gradually separate, and we see the road beyond them; now the earth at one period of her revolution is a hundred and ninety millions of miles nearer to some fixed stars, than she was six months before, yet this enormous space makes no difference betwixt any of the fixed stars; how vast then must be their distances from us!"* The brightest of the fixed stars is Sirius, but even its rays twinkle as they reach us; in this respect the fixed stars differ from the planets, whose light is steady. We have eleven stars of the first magnitude visible to us; these are found in the following constellations :— In Canis Major, one called Sirius; in Taurus, one called Aldebaron; in Gemini, Castor; in Leo, Regulus; in Virgo, Spica Virginis; in Scorpio, Antares; in Ursa Major, Dubhe; in Auriga, Capella; in Bootes, Arcturus; in Lyra, Vega; in Aquila, Altair; and in Cygnus, Deneb. In the constellations visible to the Southern hemisphere of the earth there are seven other stars of the first magnitude. These constellations are groups of stars imagined to have some resemblance to the objects whose names they bear. Since it was necessary to define the position of each star, the ancient astronomers adopted the plan of dividing the whole starry heavens into the imaginary figures of men, women, animals, and other objects; as you may see are depicted on any celestial globe. These figures have of course no corresponding limits in the sky, but they serve well enough to arrange the stars into groups or constellations, and by the aid of the device we can readily find any large star we want. Twelve of these constellations, which appear to occupy the space behind the sun as we travel round him, are called the signs of the Zodiac. Their names are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, * Rev. T. G. Hall's Exercises in Astronomy, p. 21. |