Armillary sphere The armillary sphere is an early version of the astrolabe. It is a mathematical instrument used to make astronomical calculations. Constructed from rings and hoops, it revolves on its axis to demonstrate the movement of the celestial sphere around a stationary Earth at its centre. The armillary sphere was used as early as the 2nd century AD by the astronomer and mathematician Claudius Ptolemy of Alexandria. Ptolemy’s armillary astrolabe represented the main celestial great circles with connected, pivoting, graduated bronze rings. During the 1500s, the mathematician Nicolaus Copernicus challenged the geocentric model (the basis for this instrument) with his heliocentric theory. Despite this, armillary spheres continued to be used as purely mathematical instruments during the Rennaisance and early modern periods. Further Reading Rome, A. 1927. Annales de la Société Scientifique de Bruxelles pp. 77–102 (for the armillary astrolabe).
