hour circle

American  

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.

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hour circle British  

noun

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

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hour circle Scientific  

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

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Etymology

Origin of hour circle

First recorded in 1665–75

Example Sentences

See Examples For:

hour circle

The sidereal time at any moment is the right ascension of the hour circle which at that moment coincides with the meridian.

From A Text-Book of Astronomy by Comstock, George C.

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.

From Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 7 "Horticulture" to "Hudson Bay" by Various

It is desirable that the hour circle should read approximately zero when the declination axis is horizontal, but this is not necessary for a reason soon to be explained.

From The Boy Mechanic: Volume 1 700 Things for Boys to Do by Popular Mechanics Co.

The movable hour circle and driving wheel of the Crossley reflector has two sets of graduations.

From Photographs of Nebul? and Clusters Made with the Crossley Reflector by Keeler, James Edward

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.

From Photographs of Nebul? and Clusters Made with the Crossley Reflector by Keeler, James Edward