# Orbits with Epicycles on a Deferent

Orbits with Epicycles on a Deferent

This Demonstration shows the trajectory of a planet (orange disk) around an observer (blue circle) according to the epicycle-deferent model. The large gray circle is the deferent and the smaller gray circles are the epicycles. The deferent rotates at a constant speed, and each epicycle revolves at a uniform velocity around a point on the deferent or another epicycle. By adjusting the orbital radius, rate of revolution, and initial position of each epicycle, countless orbits can be obtained that are not observed in reality.