Fourteen Weeks in Descriptive Astronomy

The Solar System

THE Solar System is mainly comprised within the limits of the Zodiac. It consists of

1. The Sun-the centre.

2. The major planets-Vulcan (undetermined), Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

3. The minor planets, at present one hundred and seventeen in number. (The paths of some extend a little outside the Zodiac.)

4. The satellites or moons, eighteen in number, which revolve around the different planets.

5. Meteors and shooting-stars.

6. Nine comets whose orbits have been computed, and over two hundred of which little is known.

7. The Zodiacal Light.

HOW WE ARE TO IMAGINE THE SOLAR SYSTEM TO OURSELVES.---We are to think of it as suspended in space; being held up, not by any visible object, but in accordance with the law of Universal Gravitation discovered by Newton, whereby each planet attracts every other planet and is in turn attracted by all First, the Sun, a great central globe, so vast as to overcome the attraction of all the planets, and compel them to circle around him; next, the planets, each turning on its axis while it flies around the sun in an elliptical orbit; then, accompanying these, the satellites, each revolving about its own planet, while all whirl in a dizzy waltz about the central orb; next, the comets, rushing across the planetary orbits at irregular intervals of time and space; and finally, shooting-stars and meteors darting hither and thither, interweaving all in apparently inextricable confusion. To make the picture more wonderful still, every member is flying with an inconceivable velocity, and yet with such accuracy that the solar system is the most perfect timepiece known.

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COMPARATIVE SIZE OF PLANETS. (Chambers.)---The following scheme will assist in obtaining a correct notion of the magnitude of the planetary system. Choose a level field or common; on it place a globe two feet in diameter for the Sun: Vulcan will then be represented by a small pin's head, at a distance of about 27 feet from the centre of the ideal sun; Mercury by a mustard-seed, at a distance of 82 feet; Venus by a pea, at a distance of 142 feet; the Earth, also, by a pea, at a distance of 215 feet; Mars by a small pepper-corn, at a distance of 327 feet; the minor planets by grains of sand, at distances varying from 500 to 600 feet. If space will permit, we may place a moderate-sized orange nearly one-quarter of a mile distant from the starting point to represent Jupiter; a small orange two-fifths of a mile for Saturn; a full-sized cherry three-quarters of a mile distant for Uranus; and lastly, a plum 1 miles off for Neptune, the most distant planet yet known. Extending this scheme, we should find that the aphelion distance of Encke's comet would be at 880 feet; the aphelion distance of Donati's comet of 1858 at 6 miles; and the nearest fixed star at 7,500 miles.

According to this scale, the daily motion of Vulcan in its orbit would be 4] feet; of Mercury, 3 feet; of Venus, 2 feet; of the Earth, 1~ feet; of Mars, 11 feet; of Jupiter, 10 inches; of Saturn, 7 inches; of Uranus, 5 inches; and of Neptune, 4 inches. This illustrates the fact that the orbital velocity of a planet decreases as its distance from the sun increases.

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Vulcan

SUPPOSED DISCOVERY.---Le Verrier, having detected an error in the assumed motion of Mercury, suggested, in the fall of 1859, that there may be an interior planet, which is the cause of this disturbance. On this being made public, M. Lescarbault, a French physician, and an amateur astronomer, stated that on March 26 of that year he had seen a dark body pass across the sun's disk, and that this might have been the unknown planet. Le Verrier visited him, and found his instruments rough and found his instruments rough and home-made, but singularly accurate. His clock was a simple pendulum, consisting of an ivory ball hanging from a nail by a silk thread. His observations were on prescription paper, covered with grease and laudanum. His calculations were chalked on a board, which he planed off to make room for fresh ones. Le Verrier became satisfied that a new planet had been really discovered by this enthusiastic observer, and congratulated him upon his deserved success. On March 20, 1862, Mr. Lummis, of Manchester, England, noticed a rapidly-moving, dark spot, apparently the transit of an inner planet. Many other instances are given of a somewhat similar character. As yet, however, the existence of the planet is not generally conceded. The name Vulcan and the sign of a hammer have been given to it. Its distance from the sun has been estimated at 13,000,000 miles, and its periodic time (its year) at 20 days.