Equinox (celestial coordinates)
The equinox moves, in the sense that as time goes forward it is in a different location with respect to the distant stars. As a result, star catalogs over the years, even over the course of a few decades, will list different ephemerides.  This is due to precession and nutation, both of which can be modeled, as well as other minor perturbing (disturbing) forces which can only be decided by observation and are this way tabulated in astronomical almanacs.