The word PLANETARIUM today usually refers to an optical or digital projection instrument that shows upon the inner surface of a hemispherical dome onto which scenes of stars, planets, sun, moon, and, in most cases, additional astronomical effects can be made to appear. The term also refers to the room or a building in which the projector is housed. In 1913, an astronomer, Max Wolf of Heidelberg Observatory, discussed with Oskar Von Miller, founder of the Deutsches Museum, the possibility of a display which would show the motions of the sun, moon and planets within a dome of spherical curvature. In this device, light comes through hole in a darkened dome under which the audience sits. Miller proposed this project to the Zeiss Works but preliminary investigations were interrupted by World War I. Following the war, Walther Bauersfeld, Zeiss Chief Engineer proposed to construct a hemispherical dome painted white interior, and to place an optical projector in the center to show the stars, sun, moon and planets together with their motions as observed from the earth. Early in 1920, Bauersfeld began to work out the design details and technical calculations. Finally, after three and a half years of design and construction, the first Planetarium Projector, Zeiss model was unveiled at the Carl Zeiss factory in Jena, Germany in August, 1923.
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