Spirograph-Epitrochoid[br]An epitrochoid is the path traced by a point on a circle (M) [br]that travels on the outside of another circle (E).[br]This can be used to model the path of the Moon (M) in orbit around the Earth (E).[br]There are about 13.3 revolutions(n) of the Moon about the Earth in one year.[br]-credit-Malin Christersson-[url]http://www.geogebratube.org/material/show/id/87141[/url]