The sky and the astrolabe
S. Battaglia and G. Miglietta

This model illustrates the principle on which the representation of the heavenly vault on a plane - a crucial element in the construction of an astrolabe - is based. A direct correlation is established between the fixed stars and their projection on the equatorial plane, where the design of the astrolabe's rete takes shape. The stars and their projections are joined by straight lines that converge on the South Pole, the ideal observation point from which the design of the rete appears to coincide perfectly with the three-dimensional vault of the heavens.