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On 2018-09-10 8:45, Antoine Couëtte wrote:
> Regarding Nutation, and since the Planetary Terms effects come to play only 
at the sub-milli arc second level, and given the 0.001" accuracy you are 
claiming with your "B" Model, I would surmise that this "B" Model of yours 
encompasses / includes / computes **all **Luni-Solar Terms, and **none** of 
the Planetary Terms. *True ?*

The SOFA documentation says,

"The full IAU 2000A (MHB2000) nutation model contains nearly 1400
terms.  The IAU 2000B model (McCarthy & Luzum 2003) contains only
77 terms, plus additional simplifications, yet still delivers
results of 1 mas accuracy at present epochs.  This combination of
accuracy and size makes the IAU 2000B abridged nutation model
suitable for most practical applications.

"The function delivers a pole accurate to 1 mas from 1900 to 2100
(usually better than 1 mas, very occasionally just outside
1 mas).  The full IAU 2000A model, which is implemented in the
function iauNut00a (q.v.), delivers considerably greater accuracy
at current dates;  however, to realize this improved accuracy,
corrections for the essentially unpredictable free-core-nutation
(FCN) must also be included.

"The IAU 2000B model includes 'planetary bias' terms that are
fixed in size but compensate for long-period nutations.  The
amplitudes quoted in McCarthy & Luzum (2003), namely
Dpsi = -1.5835 mas and Depsilon = +1.6339 mas, are optimized for
the "total nutations" method described in Note 6.  The Luzum
(2001) values used in this SOFA implementation, namely -0.135 mas
and +0.388 mas, are optimized for the 'rigorous' method, where
frame bias, precession and nutation are applied separately and in
that order.  During the interval 1995-2050, the SOFA
implementation delivers a maximum error of 1.001 mas (not
including FCN)."

Source code for the IAU 1980 and 2000B nutation models:
http://www.iausofa.org/2017_0420_C/sofa/nut80.html
http://www.iausofa.org/2017_0420_C/sofa/nut00b.html

   

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