Extract

Born at *Nicaea (1) in Bithynia, he spent much of his life in Rhodes; his recorded observations range from 147 to 127. His only extant work, the Commentary on theΦαινόμεναof Eudoxus and Aratus, in three books, contains criticisms of the descriptions and placings of the *constellations and stars by those two (see aratus(1); eudoxus(1)), and a list of simultaneous risings and settings. Valuable information on Hipparchus' own star coordinates has been extracted from it. Most of our knowledge of Hipparchus' other astronomical work comes from *Ptolemy(4)'s Almagest (see index under ‘Hipparchus’ in Toomer's trans.).Hipparchus transformed Greek astronomy from a theoretical to a practical science, by applying to the geometrical models (notably the eccentric/epicyclic hypothesis) that had been developed by his predecessors (see astronomy) numerical parameters derived from observations, thus making possible the prediction of celestial positions for any given time. In order to do this he also founded *trigonometry, by computing the first trigonometric function, a chord table.