The Milan Planetarium opened on May 20, 1930 with a Zeiss Planetarium Model II projector. The erection of the planetarium was made possible by a donation from the Italian publisher Ulrico Hoepli to the city of Milan. With its dome diameter of 19.6 m, the planetarium is still the largest planetarium in Italy and has been in operation ever since. The building with its octagonal basic shape was designed by the architect Piero Portaluppi. Since 1968, a Model IV planetarium projector has served as the centerpiece for the astronomical presentations.