Glossary of Astronomical Terms/celestial sphere

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The celestial sphere is an imaginary sphere that is much larger than the Earth and is used to identify the locations of stars and galaxies. The celestial sphere is centered on the Earth. Celestial spheres are normally defined with respect to observers, and the north celestial pole is directly above the observer. If the observer's location is not given explicitly, the north celestial pole is normally above the North Pole.