pla·ni·sphere 
(plānĭ-sfîr′)
(plānĭ-sfîr′)n.
1. A representation of a sphere or part of a sphere on a plane surface.
2. Astronomy A polar projection of half or more of the celestial sphere on a chart equipped with an adjustable overlay to show the stars visible at a particular time and place.
pla′ni·spheric (-sfîrĭk, -sfĕr-), pla′ni·spheri·cal (-ĭ-kəl) adj.