[dpsibi, depsbi, dra] = ERFA.bi00()Frame bias components of IAU 2000 precession-nutation models; part of the Mathews-Herring-Buffett (MHB2000) nutation series, with additions.
dpsibi,depsbi double longitude and obliquity corrections
dra double the ICRS RA of the J2000.0 mean equinox
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The frame bias corrections in longitude and obliquity (radians) are required in order to correct for the offset between the GCRS pole and the mean J2000.0 pole. They define, with respect to the GCRS frame, a J2000.0 mean pole that is consistent with the rest of the IAU 2000A precession-nutation model.
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In addition to the displacement of the pole, the complete description of the frame bias requires also an offset in right ascension. This is not part of the IAU 2000A model, and is from Chapront et al. (2002). It is returned in radians.
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This is a supplemented implementation of one aspect of the IAU 2000A nutation model, formally adopted by the IAU General Assembly in 2000, namely MHB2000 (Mathews et al. 2002).
Chapront, J., Chapront-Touze, M. & Francou, G., Astron. Astrophys., 387, 700, 2002.
Mathews, P.M., Herring, T.A., Buffet, B.A., "Modeling of nutation and precession: New nutation series for nonrigid Earth and insights into the Earth's interior", J.Geophys.Res., 107, B4, 2002. The MHB2000 code itself was obtained on 2002 September 9 from ftp://maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
This revision: 2021 May 11
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