Ages

Introduction

Summary

The ancient geocentric theory failed in its explanations of some observations (Retrogradation, size fluctuations and luminosity of some planets). Hipparchus ( circa 150 BC),  then Ptolemy (circa 130 AD) put forward a complicated theory about orbits that proposed the existence of  “deferents” and associated "epicycles" that the planets were supposed to follow. As you can see in this animation, you could, using these ideas,  explain at certain selected times some retrograde motion and elliptical orbits. Copernicus  (1543) was the first to drop this theory for an heliocentric one.

Goals

• To Illustrate the Ptolemaic conception of the universe.

Tags

epicycle deferent ptolemy hipparcus orbit ellipse gravitation retrogradation retrograde astronomy