An orrery is a mechanical model that represents the positions and motions of celestial bodies in the solar system. It typically illustrates the movements of the Earth, Moon, and planets around the Sun, allowing viewers to visualize their orbits and relative positions over time. Orreries can vary in complexity, from simple models to intricate devices with moving parts. These models are often used for educational purposes, helping people understand astronomy and the mechanics of the solar system. The name "orrery" is derived from the Earl of Orrey, who commissioned a notable example in the early 18th century.