Determinations of precession

Recent determinations of lunisolar precession and of the motion of the equinox are reviewed. Methods of determination are discussed which are based on proper motions referred to fundamental systems, on planetary motions, and on proper motions referred to galaxies. It is concluded that a new fundamental catalogue, which will replace the FK4 at some future date, should be based on revised values of precession and freed from errors in the motion of the equinox.Presented at IAU Colloquium No. 9, The IAU System of Astronomical Constants, Heidelberg, Germany, August 12–14, 1970.