hour angle

American  

noun

Astronomy.

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

---

hour angle British  

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 Scientific  

1. 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.

---

Etymology

Origin of hour angle

First recorded in 1830–40

Example Sentences

The hour angle of the center of the sun is the measure of apparent or solar time.

From Lectures in Navigation by Draper, Ernest Gallaudet

What is the hour angle of the sun at noon?

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

What is the hour angle of the sun when it has the greatest altitude?

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

He would read on the chronometer the hour of the meridian of Greenwich, and from it would be able to deduce the longitude by the hour angle.

From Dick Sand A Captain at Fifteen by Verne, Jules

Let also the hour angle corresponding to p be 90� − n, and the declination of the same = m, the star’s declination being δ, and the latitude ϕ.

From Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 6 "Geodesy" to "Geometry" by Various