Equatorium
An equatorium (plural, equatoria) is an astronomical calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without arithmetic operations, using a geometrical model to represent the position of a given celestial body. History In his comment on Ptolemy's Handy Tables, 4th century mathematician Theon of Alexandria introduced some diagrams to geometrically compute the position of the planets based on Ptolemy's epicyclical theory. The first description of the construction of a solar equatorium (as opposed to planetary) is contained in Proclus's fifth-century work Hypotyposis, where he gives instructions on how to construct one in wood or bronze. The earliest known descriptions of planetary equatoria are in the Latin translation of an early eleventh century text by Ibn al‐Samḥ and a 1080/1081 treatise by al-Zarqālī, contained in the Libros del saber de astronomia (Books of the knowledge of astronomy), a Castilian compilation of astronomical works collected under the patronage of Alfonso X of Castile in the thirteenth century. The Theorica Planetarum (c. 1261–1264) by Campanus of Novara is the earliest extant description of the construction of an equatorium in Latin Europe. Campanus' instrument resembled an astrolabe, with several interchangeable plates within a mater. The best