Aratus, the court poet of Macedonian King Antigonus Gonatas, lived from 315 to 240 B.C. He composed a didascalic poem entitled Phænomena, a rendering in verse of a lost work of the same title by Eudoxus of Cnidus. The Phænomena, which enjoyed enormous popularity, describe the constellations, their waxing and waning and the circles that divide up the celestial sphere. A crucial tool to assist the reader in understanding the Phænomena was the celestial globe, used to identify the physiognomy of the star groups described.