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Session 68 - Invited Talk.
Oral session, Friday, January 09
International Ballroom Center,
The European Space Agency included the Hipparcos mission within its scientific programme in 1980. Dedicated to the precise measurement of stellar positions, distances, and proper motions, the objective was the construction of a catalogue of 100,000 stars with a target accuracy of 0.002 arcsec on each of these five astrometric parameters. The Hipparcos satellite was launched in 1989, and operated until mid-1993. The products of the mission were finalised in August 1996, with a one-year proprietary period applying until June 1997, when the final data were made available: as a 17-volume printed publication (ESA SP--1200, including 6 ASCII CD-ROMs with access software); through the CDS Strasbourg (and mirror sites); and via the Hipparcos www page in ESA. The mission products comprise the Hipparcos Catalogue: 118,000 stars with a median astrometric accuracy of slightly better than 0.001 arcsec (with annexes of variable, double star, and solar system object data); and the Tycho Catalogue: slightly more than one million stars with an astrometric accuracy of typically 0.03 arcsec. These catalogues provide a definitive source of astrometric data, free from systematic parallax effects (probably below the level of 0.1 milliarcsec) and within an inertial system at a comparable accuracy level. As an indication of the data quality, some 40,000 catalogue stars have a relative distance accuracy of better than 20 per cent. A summary of the catalogue contents, and applications in various areas (such as direct distance scale determination of individual stars and open clusters, and Galactic structure and kinematics) will be illustrated.
