Fig 530.—Sizes of planets.
“Choose any well-levelled field or bowling green; on it place a globe two feet in diameter; this will represent the sun. Mercury will be represented by a grain of mustard seed on the circumference of a circle 164 feet in diameter for its orbit; Venus a pea, on a circle 284 feet in diameter; the Earth also a pea on a circle 430 feet; Mars a rather large pin’s head on a circle of 654 feet; Juno, Ceres, Vesta, and Pallas grains of sand in orbits of 1,000 to 1,200 feet; Jupiter a moderate-sized orange on a circle nearly half a mile across; Saturn a small orange on a circle four-fifths of a mile; and Uranus a full-sized cherry, or small plum, upon the circumference of a circle more than a mile and a half in diameter”
Fig. 531.—Orbits of planets.
From an inspection of the following table the relative distances of the principal planets from the sun, their diameters, and other information respecting them may approximately be obtained. The dates of the discovery of the more modern pair are added:—
| Names. | Diameters in English miles (about). | Distance from the sun (about). | Sidereal period of revolution. | Time of rotation on their axis. | Date of discovery. |
|---|---|---|---|---|---|
| d. h. m. | d. h. m. | ||||
| Mercury | 3,000 | 35,000,000 | 87 23 16 | 24 5 — | Antiquity |
| Venus | 7,500 | 66,000,000 | 224 16 50 | 23 21 21 | do. |
| Earth | 8,000 | 91,000,000 | 365 6 9 | 23 56 4 | do. |
| Mars | 4,500 | 139,000,000 | 686 23 31 | 24 37 20 | do. |
| Jupiter | 85,000 | 476,000,000 | 4,332 14 2 | 9 55 21 | do. |
| Saturn | 70,000 | 872,000,000 | 10,759 5 16 | 10 16 — | do. |
| Uranus | 33,000 | 1,753,000,000 | 30,686 17 21 | 9 30 — | Herschel, 1781. |
| Neptune | 37,000 | 2,746,000,000 | 60,126 17 5 | . . . | Leverrier and Galle, 1846. |
| The Sun | 850,000 | . . . . | . . . . | 25 7 48 |
Altogether there are a great number of planets and asteroids, which latter are minor planets circulating outside the orbit of Mars. They have nearly all classical names, such as Juno, Ceres, Vesta, Flora, Ariadne, Pallas, Pomona, Thalia, etc., and are all at distances from the sun ranging between 200,000,000 and 300,000,000 of miles, the periods of sidereal revolution ranging from 1,100 to 3,000 days, so their years must be from four times to nine times as long as ours. Altogether about two hundred of the minor planets have been discovered, and they are all very much smaller than the earth; some, indeed, being very tiny—only a few miles in diameter, but very massive. They do not appear to possess any satellites—at least, none have been discovered, for such very small bodies as they must be, supposing they exist, would be quite invisible even with our perfected instruments.
Fig. 532.—Mars.
