erfa.eo06a(date1, date2)[source]

Equation of the origins, IAU 2006 precession and IAU 2000A nutation.

date1double array
date2double array
c_retvaldouble array


Wraps ERFA function eraEo06a. The ERFA documentation is:

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 e r a E o 0 6 a
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Equation of the origins, IAU 2006 precession and IAU 2000A nutation.

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

Returned (function value):
                double    the equation of the origins in radians


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 equation of the origins is the distance between the true
   equinox and the celestial intermediate origin and, equivalently,
   the difference between Earth rotation angle and Greenwich
   apparent sidereal time (ERA-GST).  It comprises the precession
   (since J2000.0) in right ascension plus the equation of the
   equinoxes (including the small correction terms).

   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
   eraEors      equation of the origins, given NPB matrix and s


   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.