Heracleides (388-315 BC) - Greek astronomer who was the first to state that a rotating earth would account for the motion of the stars and planets in the sky. Although he still believed in a geocentric universe, his work would later be expanded upon by Aristarchus to create a heliocentric universe. Hipparchus (c. 162-126 BC) - Greek astronomer who compiled a detailed catalog of the positions of 850 stars. From this information he discovered the phenomenon known as precession. He also created detailed studies of the motions of the Moon and the Sun.