The original planetarium in the Round Tower was constructed by Ole Rømer in Paris around 1675. After his return to Denmark he placed the machine in the observatory and it was used for education. The planetarium was horizontal and could be moved with a handle.

During "The big fire" in Copenhagen, 1728, the planetarium was severely damaged, but it was reconstructed and replaced in the observatory in 1740. In 1822, the planetarium was placed in the spiral walk, where it is today. To make room for the now vertical planetarium, the radiuses of the orbits of Jupiter and Saturn were halved. After 1822 the planetarium was set in motion by a handle in the hemisphere below.

In 1929, the old backplate from 1822 was replaced and a clockwork was connected to the planetarium gear. Today, the planetarium shows the position of the planets in the Solar system.