An Etymological Dictionary of Astronomy and Astrophysics

A graphical method of depicting three-dimensional geometrical objects in two dimensions. In a → planispheric astrolabe, it is the projection of a point of the celestial sphere onto the equatorial plane, as seen from one of the poles. The center of projection is the South pole for the northern hemisphere, and the North pole for the southern hemisphere. In this operation
the projection of any circle of the sphere remains a circle on the projection plane and moreover the projection does not alter angles.

See also: → stereographic; → projection