That is the pattern the planets trace in the sky and for thousands of years people thought that was literally their path. http://en.wikipedia.org/wiki/Apparent

That is the pattern the planets trace in the sky and for thousands of years people thought that was literally their path. http://en.wikipedia.org/wiki/Apparent_retrograde_motion http://en.wikipedia.org/wiki/Apparent_retrograde_motion In the ptolemeic system, the planets were thought to move with epicycles, or "wheels within wheels". This is why astrolabes had gears attached to gears. http://en.wikipedia.org/wiki/Deferent_and_epicycle http://en.wikipedia.org/wiki/Deferent_and_epicycle Then copernicus came along and blew that all away with his heliocentric model, which was then given mathematical foundation by Johannes Kepler and his laws of planetary motion.