Hipparchus of Nicaea (/hɪˈpɑːrkəs/; Greek: Ἵππαρχος, Hipparkhos; c.190 – c.120 BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry,[1] but is most famous for his incidental discovery of precession of the equinoxes.[2] Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes, Greece. He is known to have been a working astronomer between 162 and 127 BC.[3]

Bornc.190 BC
Diedc.120 BC (around age 70)

Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity.[4][5] He was the first whose quantitative and accurate models for the motion of the Sun and Moon survive. For this he certainly made use of the observations and perhaps the mathematical techniques accumulated over centuries by the Babylonians and by Meton of Athens (fifth century BC), Timocharis, Aristyllus, Aristarchus of Samos, and Eratosthenes, among others.[6]

He developed trigonometry and constructed trigonometric tables, and he solved several problems of spherical trigonometry. With his solar and lunar theories and his trigonometry, he may have been the first to develop a reliable method to predict solar eclipses.

His other reputed achievements include the discovery and measurement of Earth's precession, the compilation of the first comprehensive star catalog of the western world, and possibly the invention of the astrolabe, also of the armillary sphere that he used during the creation of much of the star catalogue. Sometimes Hipparchus is referred to as the "father of astronomy",[7][8] a title first conferred on him by Jean Baptiste Joseph Delambre.[9]