celestial sphere

celestial sphere
the imaginary spherical shell formed by the sky, usually represented as an infinite sphere, the center of which is a given observer's position.
[1875-80]

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Apparent surface of the heavens, on which the stars seem to be fixed.

For the purpose of establishing celestial coordinate systems to mark the positions of heavenly bodies, it can be thought of as a real sphere at an infinite distance from Earth. Earth's rotational axis, extended to infinity, touches this sphere at the northern and southern celestial poles, around which the heavens seem to turn. The intersection of the plane of Earth's Equator with the sphere marks the celestial equator.

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      the apparent surface of the heavens, on which the stars seem to be fixed. For the purpose of establishing coordinate systems to mark the positions of heavenly bodies, it can be considered a real sphere at an infinite distance from the Earth. The Earth's axis, extended to infinity, touches this sphere at the north and south celestial poles, around which the heavens seem to turn. The plane of the Earth's Equator, extended to infinity, marks the celestial equator. See also hour circle; ecliptic; zenith.

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Universalium. 2010.

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