Hipparchus

Hipparchus (greek: Ἵππαρχος; ca. 190 BC – ca. 120 BC) was an astronomer, geographer, and mathematician of Ancient Greece who lived in the Hellenistic period. He was born in Nicaea (now part of Turkey), and likely died on the island of Rhodes. He was an astronomer from at least the years 147 BC to 127 BC. Hipparchus is considered the greatest ancient astronomical observer. Some people see him as the greatest overall astronomer of classical antiquity.

Hipparchus was the first Greek whose quantitative and accurate models for the motion of the Sun and Moon survive. To do this, he used the observations and perhaps the mathematical techniques accumulated over centuries by the Chaldeans from Babylonia. He had a trigonometric table, which he likely used in solving some problems of polar algebra. With his theories on the sun and moon, and his rudimentary trigonometry, he was perhaps the first person to develop a reliable method to predict solar eclipses. His other well-known achievements include the discovery of precession, and the compilation of the Hipparchus Catalog, the first comprehensive celestial catalog of the western world.

He might also have invented the astrolabe, as well as the armillary sphere (which first appeared during his century and which he used in making the star catalog). It would be three centuries before Ptolemy's synthesis of astronomy would make the work of Hipparchus obsolete; it is heavily dependent on it in many areas.

Craters on the Moon and on Mars are named for Hipparchus, as are an asteroid.