Hour-angle



noun, Astronomy.
1.
the angle, measured westward through 360°, between the celestial meridian of an observer and the hour circle of a celestial body.
noun
1.
the angular distance along the celestial equator from the meridian of the observer to the hour circle of a particular celestial body
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.

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