|
A type of celestial globe in which the sphere of the sky is represented by a skeletal
framework of intersecting circles, with the Earth at the centre. The rings in the
framework represent important circles on the celestial sphere, such as the
celestial equator and the ecliptic. Some of the rings may be movable so that the sky's
appearance at different times and at different latitudes may be reproduced. On
some armillary spheres, the positions of the brighter stars are shown by small
pointers attached to the fixed rings. The use of armillary spheres, for both
observations and demonstrations, dates from at least the third century BC.
|