right ascension

American  

noun

Astronomy.

1. the arc of the celestial equator measured eastward from the vernal equinox to the foot of the great circle passing through the celestial poles and a given point on the celestial sphere, expressed in degrees or hours.

---

right ascension British  

noun

1. α. astronomy the angular distance measured eastwards along the celestial equator from the vernal equinox to the point at which the celestial equator intersects a great circle passing through the celestial pole and the heavenly object in question Compare declination

---

right ascension Scientific  

1. The position of a celestial object east of the vernal equinox along the celestial equator. Right ascension is measured in hours, minutes, and seconds from the vernal equinox (0 hours) to the point where a great circle drawn through the object and the north and south celestial poles intersects the celestial equator. Each hour corresponds to 15° of angular distance along the celestial equator for a total of 24 hours.

2. See more at equatorial coordinate system

---

Etymology

Origin of right ascension

First recorded in 1585–95

Example Sentences

See Examples For:

right ascension

But the flight control team can read out data describing the orientation of the telescope — for example, “32 degrees right ascension, 12 degrees declination.”

From Washington Post ● Aug. 26, 2022

What is the right ascension and declination of the Sun at noon on the summer solstice in the Northern Hemisphere?

From Textbooks ● Oct. 13, 2016

Instead of latitude and longitude, however, astronomers use coordinates called declination and right ascension.

From Textbooks ● Oct. 13, 2016

What is the right ascension and declination of the autumnal equinox?

From Textbooks ● Oct. 13, 2016

The outcome, accordingly, was an apex most likely correctly placed as regards right ascension, but displaced southward by some fifteen degrees.

From A Popular History of Astronomy During the Nineteenth Century Fourth Edition by Agnes M. (Agnes Mary) Clerke