"An orrery is a mechanical device designed to demonstrate the rotation and orbital motion of the earth, and the orbital motion of the moon and the planets. The device was given the name orrery by its inventor, John Rowley, as a gesture of gratitude to the nobleman who employed himCharles Boyle, the fourth Earl of Orrery (16761731)."


For a picture of an orrery:
http://www.adlerplanetarium.org/apow/ap2003.04.07.shtml