Hipparchus was an ancient Greek astronomer of Nicaea, c190BC-c120BC. Among his work was a star catalog that classified stars by brightness, into six magnitude classes, the system which has evolved into the present magnitude system. The catalog is lost. (One ancient statute, Farnese Atlas, that depicts the constellations on a globe, has occasionally been theorized to reflect it.)
Hipparchus also made critical measurements of the seasons, the lunar cycle, and the solar year.