ABSTRACT
Thales of Miletus is generally called the founder of Greek astronomy. An important school was arising at Alexandria under the first Ptolemy, and contemporary with Autolycus were Aristyllus and Timocharis, whose observations of the relative positions of stars in the zodiac were to form the basis of a great advance in the theory of astronomy. The next astronomer of note, Hipparchus, far transcends all his predecessors and contemporaries in reputation, the effect of his work being comparable with that of Newton in its relative importance to the progress of astronomy in his time. The discovery of the 'precession of the equinoxes' marks a notable advance in the science of astronomy. The next two centuries and a half almost the only notable advance in any branch of astronomy was Julius caesar's celebrated reform of the calendar, which was afterwards left practically unaltered till the time of Pope Gregory.
