right ascension

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

noun

1. 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 α Compare declination

right ascension

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

Word History and Origins

Origin of right ascension¹

First recorded in 1585–95

Example Sentences

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

This event is also a conjunction, which in astronomy means that the planets share the same right ascension.

From The Guardian

By adjusting the right ascension of the plane ABC and rotating the axis with the angular velocity of the sun, it follows that BC will be the direction of the solar rays throughout the day.

From Project Gutenberg

Sir John Herschel, who followed up the stellar researches of his father, Sir William, in great detail, places the north pole of the Galactic plane in declination 37 degrees N., and right ascension 12 h.

From Project Gutenberg

The measurements that correspond in astronomy to terrestrial latitude and longitude are called declination and right ascension and are obviously made with reference to the celestial equator, not the ecliptic.

From Project Gutenberg