The ZEISS Model II Projector

This ZEISS II Planetarium Projector was for many years the instrument that operated at the old seat of the Rome Planetarium in the Octagonal Room at Diocletian’s Baths in Piazza d’Esedra. The optical projector was constructed by the Zeiss Company from Jena and was at the cutting edge of its era. Rome’s projector was the thirteenth Zeiss projector installed in the world. The Model II was the first planetarium projector to be widely distributed throughout the world.

The instrument was donated by Germany to Italy as part of World War One damages. It was positioned in the middle of the Sala and was surrounded by wooden seats. To one side a bench was placed that held the command panel for the motor, which was equipped with electrical instruments that had illuminated arrow indicators. The Octagonal Room had a diameter of 22 metres and its dome rose 19 metres; it was able to house 387 guests. The model II was made of two 0.5 metre diameter spheres that were joined by a long three pronged metallic cylinder that was set into a central socket that allowed for free movement in all directions. The entire projection apparatus was set on a wheeled framework that did not impede the spheres’ movements. The spheres were equipped with 31 projection lamps to represent the stars on their very same magnitude, another 11 projected the Via Lacetea (the galaxy) and a further 30 projected star system and the constellation names, the meridians, the ecliptics of the equator and those of the poles.

The disappearance of the stars on the horizon was achieved by means of sophisticated diaphragm of shutters placed on the lenses of the projection apparatus and regulated by lead counter weights. Inside the connecting cylinder the numerous projectors for the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn were positioned. The velocity of planetary movements was set that a year could run its cycle in seven or three and a half minutes. The Model II furthermore allowed observers to visualise the effects of equinox, precession, and changes in terrestrial latitude with complete representations of the southern hemisphere’s sky as well as the north’s.

The instrument, which is fully original, has been reassembled but is no longer functional. In 1980 the State Authority for Heritage decided to close the old planetarium, which had been inaugurated on 28 October 1928 by Mussolini, to restore the Sala della Minerva to permit it to become an exhibition hall. On the setting of the old planetarium’s history the projector was dismantled, packed and delivered to the University of Rome La Sapienza, which stored it at the Monteporzio Observatory. In 2000 the university handed over the cases containing the antique instrument to the Comune di Roma, which reassembled this magnificent feat of engineering so that it would adorn the entrance of the new Rome Planetarium.

In the world, only two Zeiss Model II Planetarium Projectors remain, which have had no major modifications: Rome’s projector and a Zeiss II from the original Buhl Planetarium and Institute of Popular Science in Pittsburgh, Pennsylvania USA. Buhl Planetarium’s Zeiss II was functional until dismantled and placed in storage in 2002. The Planetarium of the Royal Observatory of Belgium in Brussels operates a Zeiss II projector, which was rebuilt after World War II with some refinements. Additionally, the Osaka (Japan) Science Museum displays a non-functioning Zeiss II projector (which had undergone some modifications while in use), the first planetarium projector in Japan.

(Credit: Rome Planetarium – 2008 May 20)