This historic photograph was one of the popular images from the early days of ZEISS planetariums. It conveys to people who had not yet visited a planetarium the ambience of a live demonstration. The essential nature of this ambience included the audience, the live presenter and/or operator, the star projector and the projection of the starry sky onto the dome.. At the same time, it highlights the essential components of the ZEISS planetarium projector. Pictured here is a Model II from 1926. 

The numbers in the image denote:
4 Large projector sphere with 16 projectors for the stars of the northern sky
5 Large projector sphere with 16 projectors for the stars of the southern sky
6 Projectors for nebulae, star-clusters, and the brightest star, Sirius
7 Projectors for constellation names of the northern sky and precession scale north
8 Projectors for constellation names of the southern sky and precession scale south
9 Projector for the Milky Way North
10 Projector for the Milky Way South
11 Projector cage with the projectors for Saturn, Sun and Moon
12 Projector cage with the projectors for Jupiter, Mars, Venus and Mercury
13 Small projector sphere for ecliptic, equator and pole marker
15 Small projector sphere for meridian
17 Projector for reading the scale of years
20 Motor for precession motion
21 Motor for polar altitude motion (latitude change)
22 Slip rings for polar altitude motion
28 Speaker’s desk and switchboard for the projector control
29 Projector for the arrow-shaped pointer