Orrery, a mechanical device used to show the motions of bodies within the solar system. In an orrery, the sun, the moon, and some or all of the planets are represented by small spheres attached to wires. The spheres are moved by gears to show the relative motions of the bodies they represent.
An orrery was once considered to be a planetarium, but that term is now more properly used for special projection machines that show the motions of the stars as well as bodies within the solar system. The orrery was invented in the early 18th century by George Graham, an instrument-maker in England. The device was named for Charles Boyle, fourth Earl of Orrery, for whom one was constructed.