Planetarium projector

Two spheres on a common axis project the stars of the northern and southern hemispheres, while the cage between them carries separate Sun, Moon and planet projectors with mechanically driven orbits. Each star is a hole in a metal plate whose size sets its apparent magnitude. Unlike digital domes, an opto-mechanical projector gives point-like stars with no pixels — an image still considered the benchmark. The mechanism can accelerate time and show the sky of any date within millennia. On display in the planetarium hall; sessions run daily on a schedule.