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celestial sphere

(Encyclopedia)celestial sphere, imaginary sphere of infinite radius with the earth at its center. It is used for describing the positions and motions of stars and other objects. For these purposes, any astronomical...

celestial horizon

(Encyclopedia)celestial horizon, one axis of the altazimuth coordinate system. It is the great circle on the celestial sphere midway between the observer's zenith and nadir; it divides the celestial sphere into two...

celestial pole

(Encyclopedia)celestial pole, one of the two points at which the earth's axis of rotation intersects the celestial sphere. The celestial pole is important as a reference point in the equatorial coordinate system; t...

sphere

(Encyclopedia)sphere, in geometry, the three-dimensional analogue of a circle. The term is applied to the spherical surface, every point of which is the same distance (the radius) from a certain fixed point (the ce...

celestial meridian

(Encyclopedia)celestial meridian, vertical circle passing through the north celestial pole and an observer's zenith. It is an axis in the altazimuth coordinate system. ...

celestial equator

(Encyclopedia)celestial equator: see equatorial coordinate system. ...

celestial mechanics

(Encyclopedia)celestial mechanics, the study of the motions of astronomical bodies as they move under the influence of their mutual gravitation. Celestial mechanics analyzes the orbital motions of planets, dwarf pl...

sphere of influence

(Encyclopedia)sphere of influence, term formerly applied to an area over which an outside power claims hegemony with the intention of subsequently gaining more definite control, as in colonization, or with the inte...

equatorial coordinate system

(Encyclopedia)CE5 Equatorial coordinate system equatorial coordinate system, the most commonly used astronomical coordinate system for indicating the positions of stars or other celestial objects on the celesti...

precession of the equinoxes

(Encyclopedia)CE5 Precession of the equinoxes (the points at which the earth's celestial equator intersects its ecliptic) is due to the slow rotation of the earth's axis around a perpendicular to the ecliptic. ...