Celestial sphere
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In astronomy and navigation, the celestial sphere is an imaginary rotating sphere of "gigantic radius", concentric and coaxial with the Earth. All objects in the sky can be thought of as lying upon the sphere. Projected from their corresponding geographic equivalents are the celestial equator and the celestial poles. The celestial sphere projection is a very practical tool for positional astronomy.
In the Aristotelic and Ptolemaic models, the celestial sphere was imagined as a physical reality rather than a geometrical projection (see Celestial spheres).
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See also
- Armillary sphere
- Astronomical rings
- Celestial horizon
- Colure
- Conformal geometry
- Equinox
- Firmament
- Geocentric model
- North Star
- Pole star
- Retrograde motion
- Setting circles
- Solstice
- South Star
- Spherical Earth
- Zodiac
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