An armillary sphere is an astronomical model made from rings representing reference circles on the celestial sphere. Rotating the rings makes relations among the sky's reference planes visible in three dimensions. A central globe can represent the Earth, while inclined rings represent the apparent solar path and other celestial circles.
Royal Museums Greenwich records a 1602 instrument with eight brass rings, a horizon ring, movable solar and lunar ring systems and a small terrestrial globe. Its nested parts make the reference geometry tangible rather than merely drawing intersecting circles on paper.[ref]
Armillary sphere AST0633 by Royal Museums Greenwich. Instrument description, primary sphere and movable systems; object details AST0633, date 1602
An armillary sphere is useful for explaining why an angular coordinate depends on a chosen reference plane. It represents directions and geometric relations; its ring sizes should not be interpreted as a scale model of the distances to the Sun, Moon or stars.
Articles by others on the same topic
There are currently no matching articles.