Aristotle pushed the geocentric model of the Universe, with the Earth at the centre, and the Universe or Heavens revolving around it. Each of the Heavenly bodies – Sun, moon and planets – were attached to different sized, concentric perfect spheres with the fixed stars attached to he largest sphere. The spheres turn, each one at a slightly different speed, carrying the Heavenly objects along.
The planets though appeared sometimes to move backwards. To preserve as much as possible of the Aristotlean system, Ptolemy introduced the idea of epicycles – small circles at points on the orbit of a planet around the Earth which would preserve the motion of the planets as circles and combinations of circles.
