Hipparchus (Greek ; ca. 190 BC – ca. 120 BC) was a Greek astronomer, geographer, and mathematician. He lived in the Hellenistic period. He was born in Nicaea (now Iznik, Turkey), and probably died on the island of Rhodes. He worked as an astronomer at least from 147 BC to 127 BC. Hipparchus is considered the greatest ancient astronomical observer. Some people see him as the greatest overall astronomer of antiquity.