planetarium

Optical projection device by means of which the motions of stars and planets are reproduced on a domed ceiling representing the sky; or, more generally, any device that represents such motions, such as an orrery. Traditional projectors are being replaced by digital systems in which an image is created by computer, and then cast onto the dome by one or more projectors.

Also, a building housing such a device, usually with auditoriums and scheduled lectures. About 60 such planetariums exist in the US.