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# eect00

erfa.eect00(date1, date2)

  Equation of the equinoxes complementary terms, consistent with IAU 2000 resolutions.

  Parameters:
    date1 double array
    date2 double array
  Returns:
    c_retval double array

  Notes

  Wraps ERFA function `eraEect00`. The ERFA documentation is:

      - - - - - - - - - -
       e r a E e c t 0 0
      - - - - - - - - - -

      Equation of the equinoxes complementary terms, consistent with
      IAU 2000 resolutions.

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

      Returned (function value):
                      double   complementary terms (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.

      2) The "complementary terms" are part of the equation of the
         equinoxes (EE), classically the difference between apparent and
         mean Sidereal Time:

            GAST = GMST + EE

         with:

            EE = dpsi * cos(eps)

         where dpsi is the nutation in longitude and eps is the obliquity
         of date.  However, if the rotation of the Earth were constant in
         an inertial frame the classical formulation would lead to
         apparent irregularities in the UT1 timescale traceable to side-
         effects of precession-nutation.  In order to eliminate these
         effects from UT1, "complementary terms" were introduced in 1994
         (IAU, 1994) and took effect from 1997 (Capitaine and Gontier,
         1993):

            GAST = GMST + CT + EE

         By convention, the complementary terms are included as part of
         the equation of the equinoxes rather than as part of the mean
         Sidereal Time.  This slightly compromises the "geometrical"
         interpretation of mean sidereal time but is otherwise
         inconsequential.

         The present function computes CT in the above expression,
         compatible with IAU 2000 resolutions (Capitaine et al., 2002, and
         IERS Conventions 2003).

      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
         eraFave03    mean longitude of Venus
         eraFae03     mean longitude of Earth
         eraFapa03    general accumulated precession in longitude

      References:

         Capitaine, N. & Gontier, A.-M., Astron.Astrophys., 275,
         645-650 (1993)

         Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
         implement the IAU 2000 definition of UT1", Astron.Astrophys., 406,
         1135-1149 (2003)

         IAU Resolution C7, Recommendation 3 (1994)

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

      This revision:  2021 May 11

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