Epicycles were a way of explaining the complicated motion of the planets in a system with the Earth, rather than the Sun, at the centre of the solar system. The motion of the planets seems to vary in speed, and can at some times even appear to move 'backwards'. One way to produce this motion is to have the planets moving on circles-within-circles, and even circles-within-circles-within-circles. This applet illustrates epicycles in an exaggerated form, as well as the pretty and convoluted planetary orbits produced by these epicycles.
