celestial sphere
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The celestial sphere is an imaginary sphere of enormous size centered on wherever you are standing, onto which all the stars and planets appear to be projected in the sky. It's a useful tool for astronomers and stargazers to map and describe the positions of objects in the night sky as if they were all equally distant from Earth.
AI-generated from the Wikipedia summary — may contain errors.
Article
Visualization of a celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location.
The celestial sphere is a conceptual tool used in spherical astronomy to specify the position of an object in the sky without consideration of its linear distance from the observer. The celestial equator divides the celestial sphere into northern and southern hemispheres.