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P.T. Wallace (Space Science & Technology Department, Rutherford Appleton Laboratory, UK)
The IAU 2000 models for precession-nutation and Earth rotation offer a big step forward in accuracy. Not surprisingly, they are also larger than their predecessors (thousands of terms in some cases), but also they involve dealing with complications that previously were below practical limits on accuracy. These considerations make using standard software especially attractive, and the IAU SOFA collection provides implementations of the IAU 2000 algorithms that offer the full accuracy and yet are easy to use for everyday applications.
A striking feature of the IAU 2000 models is that the ecliptic and equinox have been downgraded in status and no longer provide the zero-point in right ascension. The new origin is a point on the celestial equator close to its intersection with the ICRS prime meridian, but defined kinematically. The counterpart of Greenwich apparent sidereal time when using this new origin is the Earth Rotation Angle, which is linearly related to UT1.
Though the new approach offers a number of advantages, stemming from the clean separation between Earth pole orientation and Earth rotation, it is sufficiently different from the existing equinox-based approach that many users will be reluctant or unable to make the switch. The SOFA routines cater for this by providing equal levels of support for both the classical equinox-based approach and for the new approach. The two options give results that agree to microarcsecond accuracy.
If you would like more information about this abstract, please follow the link to http://www.iau-sofa.rl.ac.uk/. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.
The author(s) of this abstract have provided an email address for comments about the abstract: ptw@star.rl.ac.uk
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Bulletin of the American Astronomical Society, 36 #2
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