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

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 Project Gutenberg

What is the hour angle of the sun at noon?

From Project Gutenberg

By hour angle, I mean the distance in time from your meridian to the meridian of the point or celestial body in question.

From Project Gutenberg

Seated at the same table as herself was a skilful sailor, using logarithms, secants and cosecants, polar distances and hour angles, as if he were in some university class-room.

From Project Gutenberg

The diagram represents, 1st, circles of equal altitudes; 2ndly, the path of sun, stars, etc., for each 10th degree of declination; 3rdly, the hour angles, all projected down upon--4thly--the level compass card.

From Project Gutenberg