hour circle

noun

Astronomy.

1. a great circle on the celestial sphere passing through the celestial poles and containing a point on the celestial sphere, as a star or the vernal equinox.

hour circle

noun

1. a great circle on the celestial sphere passing through the celestial poles and a specified point, such as a star

hour circle

1. A great circle passing through the poles of the celestial sphere and intersecting the celestial equator at right angles. An hour circle is equivalent to a meridian on Earth and is used in describing the position of a celestial body with respect to an observer's celestial meridian.

2. See more at hour angle

Word History and Origins

Origin of hour circle¹

First recorded in 1665–75

Example Sentences

It is equal to the angle at the pole between the hour circle through the body and the meridian, but is usually expressed in time.

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Right ascension, corresponding to terrestrial longitude, is the angular distance of a heavenly body from the vernal equinox measured on the celestial equator eastward to the hour circle passing through the body.

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The inclination of the declination axis was determined with a hanging level which had been provided by Mr. Crossley, the hour circle and polar axis being very firmly clamped.

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Note that in the map one of these hour circles is marked 0.

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To layout the hour circle, draw two parallel lines AB and CD, Fig.

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