Editing Celestial sphere (section)

{{short description|Imaginary sphere of arbitrarily large radius, concentric with the observer}}
{{for multi|the ancient cosmological model|Celestial spheres|other uses|Celestial (disambiguation)}}
[[File:Celestial Sphere - Eq w Label figures.png|thumb|Visualization of a celestial sphere]]
In [[astronomy]] and [[navigation]], the '''celestial sphere''' is an [[abstraction|abstract]] [[sphere]] that has an arbitrarily large [[radius]] and is [[concentric objects|concentric]] to [[Earth]]. All objects in the [[sky]] can be conceived as being [[projective geometry|projected]] upon the inner surface of the celestial sphere, which may be [[geocentric model|centered on Earth]] or the observer. If centered on the observer, half of the sphere would resemble a [[Sphere#Hemisphere|hemispherical]] [[projection screen|screen]] over the observing location.

The celestial sphere is a conceptual tool used in [[spherical astronomy]] to [[celestial coordinate system|specify]] the position of an [[astronomical object|object]] in the sky without consideration of its linear distance from the observer. The [[celestial equator]] divides the celestial sphere into [[northern celestial hemisphere|northern]] and [[southern celestial hemisphere|southern]] hemispheres.