Campanus

Campanus refers to a group of related astronomical instruments used for measuring celestial positions, particularly altitudes and angles. The most well-known is the Campanus astrolabe, named after the 13th-century Italian mathematician and astronomer Johannes Campanus of Novara. Campanus's work involved simplifying and explaining Ptolemy's Almagest and also described the construction and use of the astrolabe.

The Campanus astrolabe is characterized by its specific stereographic projection and the arrangement of its rete and mater. Unlike some other astrolabes, the Campanus projection places the zenith of the celestial sphere at the center of the astrolabe's face. This projection method allows for the measurement of various astronomical quantities, including the altitude of celestial bodies, time of day and night, and the azimuth of stars.

These instruments were widely used from the late Middle Ages through the Renaissance for astronomical observation, navigation, and astrological calculations. They were complex devices, typically made of brass, with intricate engravings that represented the stars and celestial circles. The Campanus astrolabe, in particular, was popular in Europe for centuries due to its perceived ease of use and the clarity of its presentation of celestial data. Its design influenced later astronomical instrument development.