Hipparcos

Hipparcos (an acronym for "High precision parallax collecting satellite") was a scientific mission of the European Space Agency (ESA), launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permits 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 fixes all six quantities needed to determine the motion of the star. The Hipparcos Catalogue, a high-precision catalogue of more than 100,000 stars, was published in 1997. The lower precision Tycho Catalogue of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000.