hour circle


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Related to hour circle: hour angle

hour circle,

in astronomy, a secondary axis in the equatorial coordinate systemequatorial coordinate system,
the most commonly used astronomical coordinate system for indicating the positions of stars or other celestial objects on the celestial sphere. The celestial sphere is an imaginary sphere with the observer at its center.
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. The hour circle of a celestial body is the great circle on the celestial spherecelestial 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 object can be thought of as being located at the point where the line of sight
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 that passes through both the body and the north celestial pole. A star's hour circle is used in determining its right ascensionright ascension,
in astronomy, one of the coordinates in the equatorial coordinate system. The right ascension of a celestial body is the angular distance measured eastward from the vernal equinox along the celestial equator to its intersection with the body's hour circle.
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 and declinationdeclination,
in astronomy, one of the coordinates in the equatorial coordinate system. The declination of a celestial body is its angular distance north or south of the celestial equator measured along its hour circle.
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.

hour circle

Any of a series of great circles on the celestial sphere along which declination is measured. The hour circle of a particular celestial body or point passes through the body or point and the north and south celestial poles. See also hour angle.

hour circle

[′au̇r ‚sər·kəl]
(astronomy)
An imaginary great circle passing through the celestial poles on the celestial sphere above which declination is measured. Also known as circle of declination; circle of right ascension.

hour circle

hour circle
Any great circle joining the celestial poles and passing through a point on the celestial sphere. All celestial bodies are positioned on particular hour circles. Unlike celestial meridians, which remain fixed with respect to the earth, hour circles move with the celestial sphere as it rotates about the earth. Also called a circle of declination or a circle of right ascension.