Armillary Sphere

Armillary Sphere, an astronomical instrument employed to illustrate the chief lines of reference in the celestial sphere, and to exhibit the apparent motions of the heavenly bodies as seen by an observer at the centre. It was much employed by the ancient astronomers, and Tycho Brahe used a modification thereof to make actual measurements; but the instrument is now rarely used, its place being generally supplied by the celestial globe (q.v.).