An orrery is a mechanical model that represents the positions and motions of celestial bodies in the solar system. It typically includes the Sun, Earth, and other planets, illustrating their orbits and relative sizes. Orreries can vary in complexity, from simple models to intricate devices that accurately depict planetary movements. These devices are often used for educational purposes, helping people understand the mechanics of the solar system. The name "orrery" comes from the Earl of Orrey, who commissioned a notable model in the 18th century. Today, orreries are popular in museums and as decorative items.