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259. The stars, according to their distances, are of seven sizes, called first magnitude, second magnitude, &c. down to the seventh magnitude, which can only be seen with a telescope The stars may be distinguished from the planets by their twinkling; whereas the planets have a steady light.
Obs. -Having now acqaired some knowledge of the wonderful things around the EARTH, which surpass the conception or imagination of man, we will return again to it, observing, that these fixed stars and other celestial objects are constantly made use of to determine the relative situation of places ; and that they are unerring guides both in regard to time and place.;
260. Besides the motion round the Sun in their respective years, the earth and the planets also turn round on their own axes and by turning to and from the Sun, produce to their inhabitants, alternate light and darkness, or day and night; so that their seasons and years are produced by the grand revolution round the Sun:
Obu-If a boy throw # ball out of his hand, besides going forwards, it turns round on its axis, and thie is the precise motion of the earth and planeta. Ho likewise the bull of a billiard-table moves onward, and also turns on its axis.
201. The distances of the seven primary planets from the Sun, in round millions, are -Mercury % 80, Venus ? 6N, Earth (03, Mars 8 142, Jupiter 7.480, Saturn h 802, and Herschel W 1,800 millions of miles from the Sun.
Their diameters are respectively 3, 8, 8, 4, 80, 79, and 36 thousand miles.
And their periods of revolution are 3, 7, 12, 22, 144, 340, and 1000 months.
202. Ju their grand orbits, the planets do trot move exactly in the same level or plane; but each moves regularly in its own level. Nor are their axes exactly perpendicular to the plate of their orbite, but variously inclined ; and this inclination produces the difference of their sea8009, and the different lengths of day and night.
203. The whole earth is calculated to be 41 tiones heavier than water; the Sun, Jupiter, and Herschel about the weight of water ; Mer.
ury wine times, and Venus six times heavier. In this way, taking matter for matter, it is found, that it would take a million of our earth, to make a body equal to the Hum.
204. Next to the sun, the Moon is that of the heavenly bodies, which the most interests our curiosity. She is but 240,000 miles distant from the earth, only 2,000 miles in diameter, and 6,300 miles in circumference. She accompanies the Earth in its annual orbit; and, duripg that period, goes herself nearly thirteen times round the Earth in an orbit of her own.
265. The Moon goes round her orbit in 27 days 8 hours; but, as the Earth moves forward during the time, it is 29 days 12 hours before she returns again to a conjunction with the Sun. The Earth is sixty times larger than the Moon; or it would require sixty moons to make up the bulk of the Earth.
266. The mountains in the Moon are, however, higher than those on the Earth. For example, Mount Leibnitz, in the Moon, is tive miles high, which is a mile higher than Chimboraço, in Peru. The surface of the Moon is, besides, covered with deep pits or vallies, some of them four miles deep. THE MOON, AS SEEN THROUGH A TELESCOPE
207. The Moon always keeps the same side towards the Earth, so that she turns once on her axis as she moves round the Earth; and her day and night are, consequently, as long as the period from new moon to full moon. But the Earth acts also as a moon to her, being at the same time far more luminous : so when it is new moon to the Earth, it is a full earth to the Moon, and the contrary,
268. As the Moon shines with no light besides that which she reflects from the Sun; it is evident, that the shape must depend on her position in regard to the Sun and Earth
When the Earth is exactly in the middle, the whole illumined side of the Moon will be towards the Earth, and it will be a full moon.
When the Moon is in the middle, her dark side will be presented to the Earth; and it will be new, or no moon.
As she proceeds from new to full, more and more of her light side will appear, or it will increase; and on going from full to new, it will, of course, decrease.
-The Moon, refulgent lamp of night, O'er heaven's clear azure spreads her sacred light, When not a breath disturbs the deep serene, And not a cloud o'ercasts the solemn scene ; Around her throne the vivid planets roll, And stars unnumber'd gild the glowing pole ; O'er the dark trees a yellower verdure shed, And tip with silver every mountain's head ; Then shine the vales; the rocks in prospect rise ; A food of glory bursts from all the skies : The conscious swains, rejoicing in the sight, Eyo ibo blue vault, and bles the useful light.
ETPLANATION. S is the Sun; T the Earth; the inner circle represents the Moon in its orbic receiving its light from the Sun. The outer circle is the portrait of the Moon in cacla adjoining part of her orbit as seen at the Earth. Thus at A it is fall moon, or all light, as nt a, and at Eit in new, or all dark, as ate, At E it is in a position to producer an eclipse of the Sun, or overshadow the Enreb i and at A to be eclipsed itself, or receive the Earth's shadow.
209. As both Earth and Moon cast long sha' dows, it is evident, if they moved on the same level, that every time the Earth passes between the Sun and Moon, the Earth's shadow. would fall on it, and darken or eclipse the Moon; and that every time the Moon passes between the Sun and Earth, the Moon's shadow would eclipse the Sun.