Hipparcos Celestial Reference Frame

The Hipparcos Celestial Reference Frame (HCRF or Hipparcos Reference Frame, HRF) is a celestial reference frame based upon data from the Hipparcos mission, an optical reference frame for use with the International Celestial Reference System (ICRS), effectively replacing earlier reference frames based upon the Catalogues of Fundamental Stars. Such reference frames provide established positions of observable astronomical objects on which to base celestial coordinates of any observable object. A more recent effort is the Gaia Celestial Reference Frame (Gaia-CRF3).