erfa.gst00a(uta, utb, tta, ttb)[source]

Greenwich apparent sidereal time (consistent with IAU 2000 resolutions).

utadouble array
utbdouble array
ttadouble array
ttbdouble array
c_retvaldouble array


Wraps ERFA function eraGst00a. The ERFA documentation is:

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 e r a G s t 0 0 a
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Greenwich apparent sidereal time (consistent with IAU 2000

   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 apparent sidereal time (radians)


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:

           uta            utb

       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

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

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

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

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

   eraGmst00    Greenwich mean sidereal time, IAU 2000
   eraEe00a     equation of the equinoxes, IAU 2000A
   eraAnp       normalize angle into range 0 to 2pi


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