Hipparchus (190-120 B.C.) was an ancient Greek astronomer who compiled first-known catalogue of stars and first map of the skies. He listed 850-1,000 stars, organized by constellation. He noted each star's position and brightness (he rated the brightness on a scale from 1 to 6, the brightest being 1). Hipparchus also devised the system of epicycles, an Earth-centered system in all celestial objects moved in perfect circles around the Earth. He also founded trigonometry.
Hipparchus (Greek ; c. 190 BC – c. 120 BC) was a Greek astronomer, geographer, and mathematician of the Hellenistic period.
The Hipparchus is a dialogue attributed to the classical Greek philosopher and writer Plato. It is now widely agreed that Plato is not the author of this work, based on stylistic and other considerations. As the name implies, the subject of this dialogue is the Athenian tyrant Hipparchus.