A mechanical device that illustrates the relative positions and motions of the planets and moons in the Solar System … typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms.
[They] can range widely in size from hand-held to room-sized. An orrery is used to demonstrate the motion of the planets, while a mechanical device used to predict eclipses and transits is called an astrarium.
He meant by this the old orrery at the top of the house, from whose round window he had looked out as the stork bearing Lilac and Mrs. Underhill had passed. Everyone told him that the machinery which operated the planets in this antiquity was clabbered thick with rust and had been immovable for years.