Definitions for: Right Ascension

[n] an arc of the celestial equator eastward from the vernal equinox
[n] (astronomy) the angular distance eastward along the celestial equator from the vernal equinox to the intersection of the hour circle that passes through the body; expressed in hours and minutes and second; used with declination to specify positions on the celestial sphere; "one hour of right ascension equals fifteen degrees"