Transcript: In the 5th century BC Anaxagoras deduced the true cause of eclipses. He realized that the curved shadow of the Earth on the Moon during a lunar eclipse supported the idea that the Earth was round.  In fact, a sphere is the only three-dimensional object that, whatever its orientation, always casts a circular shadow.  He was aware of a meteorite that had fallen in his native Greece and deduced from it that objects could move between the celestial and terrestrial spheres.  He also speculated as to the true size of the sun, saying that it might be an incandescent stone larger than the Peloponnesian peninsula. Such ideas were heretical in Greece at the time, and so he was banished for impiety.