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Astron. Astrophys. 331, L33-L36 (1998)

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Letter to the Editor

The adoption of ICRS on 1 January 1998: meaning and consequences

M. Feissel 1 and F. Mignard 2

1 IERS Central Bureau, Observatoire de Paris, URA CNRS 1125, 61 av. de l'Observatoire, F-75014 Paris, France
2 Observatoire de la Côte d'Azur, CERGA, UMR CNRS 6527, av. Copernic, F-06130 Grasse, France

Received 28 November 1997 / Accepted 9 December 1997


As of 1 January 1998, the celestial reference system adopted by the IAU will be based on a set of extragalactic directions, replacing the Fundamental Katalog No 5 (FK5) that gave star coordinates in a reference system (referred to as equator and equinox J2000) based primarily on the dynamics of the solar system. This change is deeper than a mere replacement of a reference system by a better one. It implies a drastic modification in the underlying concepts and has practical consequences at various levels for the users needing the best astrometric accuracy. The IAU decision begins a new era in the definition of reference systems and marks a sharp break with the practice of the last three hundred years characterized by the long series of fundamental star catalogues.

Send offprint requests to: M. Feissel (e-mail: feissel@obspm.fr)

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998