Noun
a celestial globe consisting of metal hoops; used by early astronomers to determine the positions of stars
Source: WordNetThe use of an armillary sphere is recorded from the 4th century BC and a sphere permanently mounted in equatorial axis from 52 BC. Source: Internet
Richer also revealed how Gerbert made the planets more easily observable in his armillary sphere: He succeeded equally in showing the paths of the planets when they come near or withdraw from the earth. Source: Internet
This armillary sphere was also described by Gerbert in a letter to his colleague Constantine. Source: Internet