ptolemys model of the universe

The word planet comes from the Greek word planetos meaning wandering star (thus, unlike the Earth, in Ptolemy s model, the Sun and Moon were planets). Because of retrograde, for centuries unexplainable movements, the heavenly bodies in Ptolemy s model does not move by ellipses but rather by curves called epicycles. This animation shows simplified Ptolemy s model of the Universe with Moon as a first, and Sun as a fourth planet orbiting around Earth. All planets except Moon and Sun are moving on epicycles whit their centres positioned on circles called deferent. Last sphere, after Saturn, is a sphere of Stars. In this particular figure, orbital periods are adjusted so they always draw the same path. The background sound is Simphonies of planets recorded by NASA Voyager.