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Astron. Astrophys. 359, 1195-1200 (2000)

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4. Accessibility of ICRS

The direct access to the extragalactic objects is most precise through VLBI observations; most sources are too faint to be successfully observed with optical instruments. Therefore, the ICRS is not widely available to all users, except if it is tied to other major reference frames. The IAU decided that the Hipparcos stellar reference frame be the realization of the ICRS in optical wavelengths (Kovalevsky et al. 1997). Furthermore, the IAU has decided that the International Earth Rotation Service and the IAU Working Group on reference frames, should assure the ties between ICRF and reference frames at others wavelengths (Andersen 1999).

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© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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