In his form of the Geocentric Theory, Ptolemaeus devised this theory by having each planet rotating in uniform in the epicycle, while making a larger rotation around the Earth, which at this time was considered to be the center of the universe, called the deferent. One half of the epicycle cycle moves counterclockwise to the deferent cycle making appear as though the planet slowed down or reversed its direction. This explains the planets retrograding, when the actual or apparent motion of a body moves in the opposite direction that the astronomical system usually moves.

 

He believed that the planets or heavenly bodies moved in circular motions previously determined by being attached to unseen spheres, thus allowing him if laid them on top of each other without any spaces between them, to discover that his calculations matched the solar and lunar distances. Thus having been named the Ptolemaic System.