Hipparcos, a satellite with the Hipparcos Catalogue and other star datasets, was a scientific mission of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permitted the accurate determination of proper motions and parallaxes of stars, allowing a determination of their distance and tangential velocity. When combined with radial-velocity measurements from spectroscopy, this pinpointed all six quantities needed to determine the motion of stars. The Hipparcos Catalogue, a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision Tycho Catalogue of more than a million stars was published at the same time, while the enhancedTycho-2 Catalogue of 2.5 million stars was published in 2000.
The word "Hipparcos" is an acronym for "High precision parallax collecting satellite" and a reference to the ancient Greek astronomerHipparchus of Nicaea, noted for trigonometry and the precession of the equinoxes.