Back Hemelbol Afrikaans كرة سماوية Arabic Esfera celeste AST Səma sferası Azerbaijani Күк сфераһы Bashkir Нябесная сфера Byelorussian Нябесная сфэра BE-X-OLD Небесна сфера Bulgarian খ-গোলক Bengali/Bangla Esfera celeste Catalan
In astronomy and navigation, the celestial sphere is an imaginary sphere (ball) of a very large unspecified size. The earth and the sphere have the same centre: they are concentric. They also rotate upon the same axis. All objects in the sky can be thought of as projected (drawn, written) upon the celestial sphere. This imaginary sphere is a very practical tool for positional astronomy.