[Gk. astron, a star; and nomos, a law.] In its widest sense, it includes everything that is known concerning the heavenly bodies. It treats of their motions, relative positions, distances, magnitudes, mutual influence, constitution, and physical condition. The history of astronomy dates back to very remote ages. The Chinese, Hindus, Babylonians, and Egyptians each possessed some knowledge of the science, and had made some progress in astronomical observation many centuries before the commencement of the Christian, era. It was first raised to the dignity of a science among the Greeks. The most eminent among ancient astronomers was Hipparchus, who discovered the precession of the equinoxes and other facts of importance. Ptolemy, the next astronomer of note, founded the system which makes the earth the centre of the universe, around which the mighty circle of the heavens revolves once in twenty-four hours. Copernicus (1473-1543) showed the error of this theory, and made the sun the centre of the solar system, the earth and the other planets revolving around it. The science has been much advanced by Tycho Brahe, Kepler, Galileo, New-ton, Herschell, and many others of note, while the instruments of observation have increased in power until the universe has been explored to remote depths and hundreds of facts concerning its constitution discovered. Most marvelous among these are the vast number and immense distances asunder of the stars, and the wonderful discovery, which we owe to spectrum analysis, that our sun, and the fixed stars, which are the suns of other solar systems, are largely or wholly made up of the chemical elements found in the earth - such as hydrogen, iron, and others.