a Greek astronomer, the place of whose birth, and the exact period when he flourished, it is impossible to determine. He must have lived at least before the time of Meton, 433 B.C. Harpalus is known for an attempt to fix the cycle which the sun and moon require to run before they reach the point from which they started. Before his time, Cleostratus had fixed it at eight years, but he added another and made it nine. It was Meton, however, who discovered that the cycle was really nineteen years. (Festus Avienus.)