catalog equinoxThe intersection of the hour circle of zero right ascension of a star catalog with the celestial equator. It is thus the origin of right ascension of the catalog. It is usually an approximation to the dynamical equinox of some date, differing from it as a result of the limits of observational accuracy. There is also a difference, over a period of time, due to the motion of the dynamical equinox; this time-dependent difference is called equinox motion.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006