Hipparch us

Tyrant of Athens, slain 514 B.C. See HIPPIAS. Hipparch us, 2d century B. C. Greatest of ancient astronomers. fore his time astronomy had been limited to knowledge of a number of isolated phenomena, some empirical rules for predicting eclipses and other occurrences, and many vague speculations of philosophers. Through him it was raised to the rank of a true science. Among his discoveries were the eccentricity of the orbits of the sun and moon, the prece ion of the equinoxes, the inequality in the length of the solar day. He determined with much accuracy the true length of the year, the obliquity of the ecliptic, and the amount of the prece ion; first used eclipses of the moon for determining longitude, and formed Hip Knob. IMG:content-0600.png:[blocks in formation] the first catalogue of stars, the number being 1,080. A complete account of his work would embrace most of what was known of astronomy at that time.