A term that has two interrelated meanings: (1) the building that houses a hemispherical domed theater that displays the motions of the sky (stars, Sun, Moon, and planets) as viewed from Earth, and displays (in the modern digital planetarium) the relative position of Earth in space; and (2) the projector that generates these astronomical views. The planetarium projector can be an optomechanical device, a digital video projection system, or a combination of both, popularly called a hybrid planetarium system.