“The” New American Grammar Of The Elements Of Astronomy, On An Improved Plan

OF THE SOLAR SYSTEM, AND THE FIRMAMENT OF THE FIXED STARS.

CHAPTER I.

Of the bodies which compose the solar system.

1. The SOLAR SYSTEM consists of the Sun in the centre; and of eleven primary planets, which, taken in the order of their proximity to that luminary, are Mercury, Venus, the Earth Mars 8, Juno, Vesta, Ceres, Pallas, Jupiter 14, Saturn, and Uranus or Herschel

These are called primary planets, because they perform revolutions round the sun in their respective periodic times. The four planets, Juno, Vesta, Ceres, and Pallas, are sometimes called minor planets or asteroids.

2. It also contains eighteen other small planets, that revolve round several of the primary ones, and on that account are called secondary planets or satellites; besides a considerable but indeterminate number of COMETS.

The Moon is therefore considered as one of these secondary planets, or satellites, because she performs her revolutions round the Earth; the rest are, the four satellites or moons of Jupiter, the seven satellites of Saturn, and six belonging to the planet Uranus or Herschel. All the planets, both primary and secondary, are opaque bodies, which borrow their light from the Sun.

The solar or planetary system, is usually confined to narrow bounds; the stars, on account of their immense distance, and the little relation they seem to bear to us, being accounted no part of it.

3. The primary planets all revolve eastward, or in the order of the signs of the zodiac, round the sun as a centre, in elliptic orbits, or paths

which are nearly circular. All these orbits, ex cept that of the Earth, lie in planes different from that of the ecliptic, and the angle which the plane of any makes with that of the ecliptic, is called the inclination of that orbit.

4. Mercury, the nearest planet to the sun revolves round that luminary in about 88 days, at the mean distance of 37 millions of miles.

For the exact duration of the sidereal revolutions of the planet, the student is referred to the table towards the end of this chapter.

The period of time which a planet employs during its sidereal revolution, or in passing from any fixed star till its returning to the same again, is the length of that planet's year.

5. Venus revolves round the sun in about 225. days, at the mean distance of 69 millions of miles.

6. The Earth revolves round the sun in about 365 days, at the mean distance of 95 millions of miles. 7. Mars completes his revolution in about 687 days, at the mean distance of 145 millions of miles. S. Vesta completes a revolution in about 1335 days, at the mean distance of 225 millions of miles. 9. Juno, in 1591 days, at the mean distance of 253 millions of miles.

10. Ceres, in 1681 days, at the mean distance of 262 millions of miles.

11. Pallas, in 1682 days, at the mean distance of 263 millions of miles.

12. Jupiter, in about 4333 days, at the mean distance of 494 millions of miles.

13. Saturn, in about 10,759 days, at the mean distance of 906 millions of miles.

14. Uranus or Herschel, in about 30,689 days, at the mean distance of 1822 millions of miles.

The two planets, Mercury and Venus, are called inferior planets, because their orbits are included in that of the Earth, and because they perform their revolutions in less than a year.

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The eight planets, Mars, Juno, Vesta, Ceres, Pallas, Jupiter, Saturn, and Uranus, require a longer period than a year to complete their revolutions round the Sun; and as their orbits include that of the Earth, they are called superior planets.

15. The Moon, the Satellites of Jupiter, Saturn, and Uranus, describe orbits round their respective primaries, similar to those which the planets describe round the sun.

16. The motions of the Comets are very complicated; their orbits, instead of being nearly circular, like those of the planets, are very eccentric. Sometimes a comet approaches so near the sun as to be hid in his rays; at other times, it recedes from that luminary so far as to be carried beyond the planetary system, and does not return for several hundred years.

The comets are opaque bodies, which borrow their light. from the sun; they are principally distinguished from the planets by their tails, or some hairy or nebulous appearance, and their always disappearing after having been visible only for a few months.

TABLE.

Of the sidereal revolutions of the primary planets.

Days. Years. Days. Hours. Min. Sec.

Mercury

87.96926 0 87 23 15 44

Venus

224.70082

Ο 224 16 49 11

The Earth