Sosigenes the Peripatetic

Sosigenes the Peripatetic was a philosopher who lived in the 2nd century AD. He followed the Aristotelian school of thought, and was one of the first people to write interpretations and commentaries to Aristotle's work.

He was the tutor of Alexander of Aphrodisias, and wrote a work On Revolving Spheres. On 4th September 164 AD, he watched an 'annular' solar eclipse. He noticed that, unlike a total solar eclipse, the apparent size of the moon was smaller than that of the sun. This meant the distances between the sun, moon and earth were not the same at different eclipses. For this reason, sun and moon could not be on a circular movement around the same centre.

This was a significant discovery. It pinpointed a difficulty with the theory that the earth was the centre of the known universe. Much later, Nicolaus Copernicus used the same idea when he proposed a heliocentric view. In this view, the earth, moon and the planets rotate around the sun, which does not move.