hour circle definition of hour circle in the Free Online Encyclopedia.

hour circle, in astronomy, a secondary axis in the 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 celestial sphere . The celestial sphere is an imaginary sphere with the observer at its center.
..... Click the link for more information. . The hour circle of a celestial body is the great circle on the celestial sphere 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.
..... Click the link for more information. that passes through both the body and the north celestial pole. A star's hour circle is used in determining its right ascension right 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 .
..... Click the link for more information. and declination declination, 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 [′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.