An instrument used since ancient times to demonstrate and observe the movements of the heavens. It consists of a number of rings (armillaries) representing celestial great circles such as the meridian, horizon, celestial equator, and ecliptic, arranged to form a skeletal celestial sphere. Armillary spheres can still be found in the form of equatorial sundials, in which the ring representing the celestial equator is marked with hours. The name comes from the Latin word armilla, meaning ‘ring’ or ‘bracelet’.
Subjects: History — Astronomy and Astrophysics.