What is "celestial longitude"

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" [syn: right ascension, RA]

A celestial longitude is a component of any of five celestial coordinate systems, which measures the angle between an astronomical object and that coordinate system's primary direction. See here for a table detailing the elements of celestial coordinate systems, including each's celestial longitude.