Planispheric projection of the celestial sphere
S. Battaglia and G. Miglietta

The exhibit shows three different kinds of projection of the celestial sphere through the projection of the shadow of an armillary sphere.

Polar stereographic projection
described by Ptolemy, its projection point is situated at the South Pole.

Equatorial stereographic projection
in use in the Middle Ages and the Renaissance, its projection point is situated on the equator, at the equinoctial colure.

Gnomonic projection
in use since antiquity, its projection point is located at the centre of the sphere.