The Fifth Fundamental Catalogue (FK5)

A fundamental reference frame published in 1988, giving precise positions and proper motions for 1,535 bright stars on the equinox and epoch J2000. FK5 was the optical standard of its era, but it rested on a limited number of stars; it was superseded when the ICRS, realised by Hipparcos and later Gaia, replaced star-based frames with an extragalactic one.