3.5 Equinox for Coordinates [Equinox]

The year of the equator and equinox to which the coordinates are referred must be J2000 (Julian).

It is not necessary to apply precession corrections to coordinates from positional catalogs. The Guide Star Catalog and the Hipparcos Input Catalogue both use the J2000 equinox. (Note, however, that the Hipparcos output catalogue is epoch 1991.25, which means proper motions can have significant effects if you are not careful.)

For some notes on Equinox, Epoch, and units, see Section 3.13 .