Gilded brass astrolabe from circa 1500, 13.4 diameter, on display in the Museo Storia Scienza, Firenze, Italy. The astrolabe is a historical astronomical instrument used by classical astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars; determining local time (given local latitude) and vice-versa; surveying; and triangulation.