quent error in apparent place of Sun, called "aberration of light,” = 20-25", consequently Velocity of light = 192,000 miles in 1 second. Precession of the equinoxes in length in one year, = 50·1. Complete revolution of equinoxial points = 25,868 years. Constitution, rocky mass cooling down by radiation from a primitive molten condition. Condition of surface-much diversified by water and dry land, and their actions upon each other. Atmosphere-height 50 miles. Atmosphere-pressure 15lbs. on square inch. Atmosphere-maximum effect of refraction at the horizon in distorting the appearance of heavenly bodies = 34' 7". = Atmosphere-clouds, height of the Denser, under 0.5 miles; of the 2. THE MOON,-Symbol, (. Shape, spherical. Size =2160 miles in diameter. Volume (Earth unity) = 0·018. Weight (Earth unity) = 0.012517. Mean specific gravity (cubic foot of material) = 0.619. Illuminating power (Moon full, and at mean distance), by light reflected from the Sun, = 1 wax candle at 12 feet distance. Brightness (Sun unity) = 0·000033. Heat inappreciable. Greatest distance = 250,000 miles. Excentricity of orbit = 0·055. Mean synodical revolution, or that which determines the phases, 29.53 days. = Mean sidereal revolution, i.e. the return of the Moon to the same place among the stars, = 27.32 days. = Revolution on axis = time of revolution round Earth, Constitution, rocky, volcanic, mountainous, perfectly dry, and long since cooled down from a state of melting heat, Condition of surface, unchanging. Atmosphere, inappreciable, and clouds, none: so that with like illumination from the Sun, the mountains and valleys are always equally well seen in the telescope, e 3. THE SUN,-SYMBOL O. Shape, spherical. Size = 883,000 miles in diameter. = = Specific gravity (Earth unity) = 0·25. Illuminating power (at Earth's distance of 95,000,000 miles) 5570 wax candles at 1 foot distance. Colour, white, by accumulation and combination of proportionate quantities of red, yellow, and blue rays. Intensity of heat, greater than any artificial mode of production. Rotation on axis = 25 days. Inclination of axis to plane of ecliptic = 7° 30'. Greatest distance = 96,600,000 miles. Mean distance = 95,000,000 miles. Least distance = 93,400,000 miles. Mean apparent diameter 32′ 1.8". Constitution—a dark and perhaps cool central body; coated with an atmosphere, very dense, and containing several concentric strata of compact clouds. Photosphere-the outer stratum of cloud, the external edge of which is, to us, the visible surface of the Sun, and gives out all the light and heat which we feel. Condition of surface-extreme agitation and incandescence, as from excessive heat. |