orrery

An orrery is a mechanical model of the solar system, traditionally operated by a spring and gears, moving arms attached to spheres representing the Sun, planets and perhaps moons, constructed so as to move them with the same relative motions as within the actual solar system. The radii of the spheres are generally set to a different scale than that of the orbits (and the orbits and sphere-radii were sometimes not to scale at all): the actual relative sizes and distances make using a single scale impractical. Mechanical orreries using clock technology have been built for centuries. (The word orrery comes from the place-name, Orrery, in County Cork, Ireland: an Earl of Orrery was recipient of such a mechanical model.)

The term orrery has been borrowed for software or videos that display such motions on a screen, particularly for those showing models of other planetary systems, often created showing more than one such system on a single screen. A series of such video orreries showing Kepler Telescope discoveries (Kepler Orrery I, II, etc.) have displayed summaries of Kepler discoveries, simultaneously showing numerous planetary systems with their orbital motions, shown next to each other on the screen.