May 7, 1925, saw the debut of the projection planetarium at the Deutsches Museum in Munich, Germany. The first planetarium of its kind, it featured the Zeiss Model I projector, a triumph of engineering that projected 4,500 stars onto the dome – plus the Milky Way, the Sun, the Moon, and five of the planets. Its movements were driven by gears and motors operated by the educator narrating the program, giving it the ability to replicate the changing of the skies based on seasons and Earth rotation.
The projection planetarium revolutionized astronomy education, helping the public standing inside the dome at the Deutsches Museum better understand the systems that made up the heavens. Word spread, fueled by postcard images of the pioneering institution, and soon other museums and schools were building their own planetariums. Today, over 4,000 exist around the world, and May 7 is recognized as the International Day of Planetariums.
