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# gmst00

erfa.gmst00(uta, utb, tta, ttb)

  Greenwich mean sidereal time (model consistent with IAU 2000 resolutions).

  Parameters
    uta double array
    utb double array
    tta double array
    ttb double array
  Returns
    c_retval double array

  Notes

  Wraps ERFA function `eraGmst00`. The ERFA documentation is:

      - - - - - - - - - -
       e r a G m s t 0 0
      - - - - - - - - - -

      Greenwich mean sidereal time (model consistent with IAU 2000
      resolutions).

      Given:
         uta,utb    double    UT1 as a 2-part Julian Date (Notes 1,2)
         tta,ttb    double    TT as a 2-part Julian Date (Notes 1,2)

      Returned (function value):
                    double    Greenwich mean sidereal time (radians)

      Notes:

      1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both
         Julian Dates, apportioned in any convenient way between the
         argument pairs.  For example, JD(UT1)=2450123.7 could be
         expressed in any of these ways, among others:

                Part A         Part B

             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 (in the case of UT;  the TT is not at all critical
         in this respect).  The J2000 and MJD methods are good compromises
         between resolution and convenience.  For UT, the date & time
         method is best matched to the algorithm that is used by the Earth
         Rotation Angle function, called internally:  maximum precision is
         delivered when the uta argument is for 0hrs UT1 on the day in
         question and the utb argument lies in the range 0 to 1, or vice
         versa.

      2) Both UT1 and TT are required, UT1 to predict the Earth rotation
         and TT to predict the effects of precession.  If UT1 is used for
         both purposes, errors of order 100 microarcseconds result.

      3) This GMST is compatible with the IAU 2000 resolutions and must be
         used only in conjunction with other IAU 2000 compatible
         components such as precession-nutation and equation of the
         equinoxes.

      4) The result is returned in the range 0 to 2pi.

      5) The algorithm is from Capitaine et al. (2003) and IERS
         Conventions 2003.

      Called:
         eraEra00     Earth rotation angle, IAU 2000
         eraAnp       normalize angle into range 0 to 2pi

      References:

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

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

      This revision:  2021 May 11

      Copyright (C) 2013-2021, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.