xys06a¶

erfa.xys06a(date1, date2)[source]¶

For a given TT date, compute the X,Y coordinates of the Celestial Intermediate Pole and the CIO locator s, using the IAU 2006 precession and IAU 2000A nutation models.

Parameters:

date1double array
date2double array

Returns:

xdouble array
ydouble array
sdouble array

Notes

Wraps ERFA function eraXys06a. The ERFA documentation is:

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 e r a X y s 0 6 a
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For a given TT date, compute the X,Y coordinates of the Celestial
Intermediate Pole and the CIO locator s, using the IAU 2006
precession and IAU 2000A nutation models.

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

Returned:
   x,y          double  Celestial Intermediate Pole (Note 2)
   s            double  the CIO locator s (Note 3)

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.

2) The Celestial Intermediate Pole coordinates are the x,y components
   of the unit vector in the Geocentric Celestial Reference System.

3) The CIO locator s (in radians) positions the Celestial
   Intermediate Origin on the equator of the CIP.

4) Series-based solutions for generating X and Y are also available:
   see Capitaine & Wallace (2006) and eraXy06.

Called:
   eraPnm06a    classical NPB matrix, IAU 2006/2000A
   eraBpn2xy    extract CIP X,Y coordinates from NPB matrix
   eraS06       the CIO locator s, given X,Y, IAU 2006

References:

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

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

This revision:  2021 May 11

Copyright (C) 2013-2023, NumFOCUS Foundation.
Derived, with permission, from the SOFA library.  See notes at end of file.

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