Celestial Pole Offsets: Conversion From (dX, dY) to (d(psi), d(epsilon). Version 3
NAVAL OBSERVATORY WASHINGTON DC
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Resolutions B1.6-B1.8 of the 2000 IAU General Assembly established the IAU 2000A precession-nutation model defined more precisely what is meant by the celestial pole and provided a new definition of UT1 in terms of an angle that directly measures the rotation of Earth in the celestial reference system. These resolutions represent major changes in the way in which the instantaneous orientation of the Earth is to be computed. In particular, the equinox is no longer a fundamental reference point and sidereal time is no longer needed for this computation. However, Resolution B1.8 contains the following provision ...the IERS will continue to provide users with data and algorithms for the conventional transformations. Thus, the IERS International Earth Rotation and Reference Systems Service has published a new expression for sidereal time consistent with the new definition of UT1....Thus, in the long term, only dX and dY will be available from the IERS.