hour angle

hour angle

noun Astronomy.
the angle, measured westward through 360°, between the celestial meridian of an observer and the hour circle of a celestial body.


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World English Dictionary
hour angle
the angular distance along the celestial equator from the meridian of the observer to the hour circle of a particular celestial body

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
hour angle  
The angular distance, measured westward along the celestial equator, between the celestial meridian of the observer and the hour circle passing through a celestial body. A body's hour angle is measured in hours, minutes, and seconds, and corresponds to its right ascension as measured with respect to the observer's meridian (which changes with time) rather than the vernal equinox (which is fixed on the celestial equator). A celestial object that crossed the observer's meridian 3 hours and 20 minutes ago has an hour angle of +3 hours 20 minutes. An object that will not cross the meridian for another 3 hours and 20 minutes has an hour angle of -3 hours 20 minutes.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica

hour angle

in astronomy, the angle between an observer's meridian (a great circle passing over his head and through the celestial poles) and the hour circle (any other great circle passing through the poles) on which some celestial body lies. This angle, when expressed in hours and minutes, is the time elapsed since the celestial body's last transit of the observer's meridian. The hour angle can also be expressed in degrees, 15 of arc being equal to one hour. See also right ascension.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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