Epicycle

Epicycle, in the older systems of astronomy, was an arrangement for representing the motions of the heavenly bodies. The sun, moon, and planets were first conceived to revolve round the earth in circles (the perfect figure); when this assumption failed to explain the phenomena it was assumed that they moved in circles the centre of which revolved round the earth (epicycles, or "circles upon circles"). Further epicycles on these second circles were added with the progress of observation, till the whole complicated scheme was swept away by. Kepler (q.v.).