(From the Greek
"astrer" [star] and "labin" [to take].)
An astronomical instrument used by ancient Greeks and others to measure
the height above the horizon of celestial bodies. The Seaman's astrolabe
was a simple device used for measuring the altitude of the sun or a star
for fixing one's approximate latitude. It consists of a heavy brass ring
fitted with an alidade or sighting rule pivoted at the center of the ring.
Suspended vertically from a shackle at the top of the ring, the alidade
was positioned to sight the sun or star and the angle was read off on-scale
marks on the ring.
