An orrery is a mechanical model of the solar system that illustrates the relative positions and motions of the planets and moons. It is named after Charles Boyle, 4th Earl of Orrery, who commissioned the first one in 1704. The term 'planetarium' is derived from the Latin word for 'wandering star, ' and it refers to a building or theater that houses a large-scale model of the solar system. Planetariums are used to educate people about astronomy and space exploration.