Greek astronomer and mathematician who invented trigonometry and calculated the lengths of the solar year and the lunar month. He discovered the precession of the equinoxes, made a catalogue of 850 fixed stars, and advanced Eratosthenes' method of determining the situation of places on the Earth's surface by lines of latitude and longitude.
Hipparchus was born in Nicaea, Bithynia (now in Turkey), and lived on the island of Rhodes and in Alexandria, Egypt.
In 134 BC Hipparchus noticed a new star in the constellation Scorpio, a discovery which inspired him to put together a star catalogue - the first of its kind. He entered his observations of stellar positions using a system of celestial latitude and longitude, and taking the precaution wherever possible to state the alignments of other stars as a check on present position. He classified the stars by magnitude (brightness). His finished work, completed in 129 BC, was used by Edmond Halley some 1,800 years later.