Aristarchos was the first astronomer to maintain that the Earth rotates - more than two thousand years before Copernicus.

Aristarchos of Samos hypothesized that the earth is not the center of the universe, but revolves yearly about the sun and daily rotates about its own axis. On this ground, Cleanthes, the philosopher, declared that he should be indicted for impiety.

Aristarchos also wrote a book about the distances and sizes of the sun and moon which he underestimated greatly.