ASTRONOMY

(Yunanca köken — orijinale bakınız.) The science which treats of the motions, distances, arrangement,and magnitudes of the celestial bodies; of their constitution and physical condition, and, in general, of whatever can be known respecting them. There is no branch of human knowledge of which the results appear at first sight more at variance with the impre ions of our senses. The first aspect of the heavens leads us almost irresistibly to imagine ourselves placed in the centre of a starry sphere; which, in its diurnal revolution, carries along with it all the heavenly bodies. But the changes of relative position which some of the most re mark able among them continually undergo, soon make it evident that they do not all belong to the same sphere. Further observation and reflection lead us to conclude that the apparent daily revolution of the firmament is merely an illusion occasioned by the diurnal rotation ol our own earth, which, instead of remaining fixed at the centre, is carried forward about the sun with a velocity of about 19 miles in a second of time, more than eight timet that of a cannon-V)all when it leaves the mouli of a cannon The sun, which appears to be of very moderate dimen sions, is a body whose volume is 1,364,470 tin than that of the earth, and placed at a distance of 95,000,000 of miles; and the stars, which even in the best tell scopes appear only as luminous points, are bodies of the same nature as the sun; many of them, probably, far surpa ing it in magnitude. Different Cla es of Heavenly Bodies. By far the greater part of the celestial bodies appear to lie fixed in the firmament, and to preserve invariably the same relative pos i tions. These are the fixed stars. A second cla comprehends a small number which are continually shifting their positions among the stars, and are perceived to accomplish a complete revolution of the sphere in stated [s. 112]