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eraXy06

[x, y] = ERFA.xy06(date1, date2)

X,Y coordinates of celestial intermediate pole from series based on IAU 2006 precession and IAU 2000A nutation.

Given:

   date1,date2  double     TT as a 2-part Julian Date (Note 1)

Returned:

   x,y          double     CIP X,Y coordinates (Note 2)

Notes:

  1. The TT date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=2450123.7 could be expressed in any of these ways, among others:
          date1          date2

       2450123.7           0.0       (JD method)
       2451545.0       -1421.3       (J2000 method)
       2400000.5       50123.2       (MJD method)
       2450123.5           0.2       (date & time method)

The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date & time methods are both good compromises between resolution and convenience.

  1. The X,Y coordinates are those of the unit vector towards the celestial intermediate pole. They represent the combined effects of frame bias, precession and nutation.

  2. The fundamental arguments used are as adopted in IERS Conventions (2003) and are from Simon et al. (1994) and Souchay et al. (1999).

  3. This is an alternative to the angles-based method, via the ERFA function eraFw2xy and as used in eraXys06a for example. The two methods agree at the 1 microarcsecond level (at present), a negligible amount compared with the intrinsic accuracy of the models. However, it would be unwise to mix the two methods (angles-based and series-based) in a single application.

Called:

   eraFal03     mean anomaly of the Moon
   eraFalp03    mean anomaly of the Sun
   eraFaf03     mean argument of the latitude of the Moon
   eraFad03     mean elongation of the Moon from the Sun
   eraFaom03    mean longitude of the Moon's ascending node
   eraFame03    mean longitude of Mercury
   eraFave03    mean longitude of Venus
   eraFae03     mean longitude of Earth
   eraFama03    mean longitude of Mars
   eraFaju03    mean longitude of Jupiter
   eraFasa03    mean longitude of Saturn
   eraFaur03    mean longitude of Uranus
   eraFane03    mean longitude of Neptune
   eraFapa03    general accumulated precession in longitude

References:

Capitaine, N., Wallace, P.T. & Chapront, J., 2003, Astron.Astrophys., 412, 567

Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855

McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003), IERS Technical Note No. 32, BKG

Simon, J.L., Bretagnon, P., Chapront, J., Chapront-Touze, M., Francou, G. & Laskar, J., Astron.Astrophys., 1994, 282, 663

Souchay, J., Loysel, B., Kinoshita, H., Folgueira, M., 1999, Astron.Astrophys.Supp.Ser. 135, 111

Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.