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|armillary sphere |
An early astronomical device made of fixed and movable rings representing circles of the celestial sphere, such as the ecliptic and the celestial equator. It was used as early as the third century BCE as both a teaching instrument and an observational tool.
early astronomical device for representing the great circles of the heavens, including in the most elaborate instruments the horizon, meridian, Equator, tropics, polar circles, and an ecliptic hoop. The sphere is a skeleton celestial globe, with circles divided into degrees for angular measurement. In the 17th and 18th centuries such models-either suspended, rested on a stand, or affixed to a handle-were used to show the difference between the Ptolemaic theory of a central Earth and the Copernican theory of a central Sun.