the name for a stereographic projection of the sphere, either upon the plane of the equator, the eye being supposed to be in the pole of the world; or upon the plane of the meridian, when the eye is supposed in the point of the intersection of the equinoctial and horizon.

Astrolabe is also the name of an instrument formerly used for taking the altitude of the sun or stars at sea.

among the ancients, was the same as our armillary sphere.