Planetarium Projector - 1960s

1960s

A good example of a "typical" planetarium projector of the 1960s was the Universal Projection Planetarium type 23/6, made by VEB Carl Zeiss Jena in what was then East Germany. The planetarium projector was a 13-foot (4.0 m)-long dumbbell-shaped object, with 29-inch (740 mm)-diameter spheres attached at each end representing the night sky for the northern and southern hemispheres. Connecting the two spheres was a framework that held nearly 150 individual projectors, including those dedicated to the planets, the Sun, and specific stars.

Each globe held representations of almost 4,500 stars per hemisphere. The "stars" were created by tiny holes that were punched into copper foil, ranging from 0.023 to 0.452 mm in size, the larger holes letting more light get through and thereby creating brighter star images. Two glass plates held this foil between them to create what was called a "star field plate". Each globe was illuminated using a 1,500-watt lamp that was located in its center. A number of aspherical condenser lenses were placed within each globe to focus the light onto the plates. Twenty-three of the most prominent stars had their own projectors, designed to project a small disk instead of pinpoint of light, and were also colored: Betelgeuse and Antares would appear reddish, Rigel and Spica would each have a blue tinge. An image of the Milky Way was created by using drum-type projectors that were studded with unfocused pinprick-sized holes based on photographic images of our galaxy. Specific projectors could imitate the light changes of such variable stars as Algol or Omicron Ceti, and other projectors could produce images of the constellations, of specific historical comets, compass points and other astronomical phenomena. When a particular star or planet dipped below the artificial horizon, a gravity-based mercury-filled shutter would be activated, blocking out the light.