GST00B Function

  1. astro_module.f90
  2. astro_module
  3. GST00B

public function GST00B(uta, utb) result(gast)

Greenwich Apparent Sidereal Time (consistent with IAU 2000 resolutions but using the truncated nutation model IAU 2000B).

Status: support routine.

Notes

  1. The UT1 date UTA+UTB is a Julian Date, apportioned in any convenient way between the argument pair. For example, JD=2450123.7 could be expressed in any of these ways, among others:

         UTA            UTB

 2450123.7D0        0D0        (JD method)
  2451545D0      -1421.3D0     (J2000 method)
 2400000.5D0     50123.2D0     (MJD method)
 2450123.5D0       0.2D0       (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 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 routine, called internally: maximum accuracy (or, at least, minimum noise) 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. The result is compatible with the IAU 2000 resolutions, except that accuracy has been compromised for the sake of speed and convenience in two respects:

    • UT is used instead of TDB (or TT) to compute the precession component of GMST and the equation of the equinoxes. This results in errors of order 0.1 mas at present.

    • The IAU 2000B abridged nutation model (McCarthy & Luzum, 2001) is used, introducing errors of up to 1 mas.

  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.

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. & Luzum, B.J., "An abridged model of the precession-nutation of the celestial pole", Celestial Mechanics & Dynamical Astronomy, 85, 37-49 (2003)

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

History

  • IAU SOFA revision: 2007 December 8

Arguments

TypeIntentOptionalAttributesName
real(kind=wp), intent(in) :: uta

UT1 as a 2-part Julian Date (Notes 1,2)
real(kind=wp), intent(in) :: utb

UT1 as a 2-part Julian Date (Notes 1,2)

Return Value real(kind=wp)

Greenwich apparent sidereal time (radians)


Calls

proc~~gst00b~~CallsGraph proc~gst00b GST00B proc~anp ANP proc~gst00b->proc~anp proc~ee00b EE00B proc~gst00b->proc~ee00b proc~gmst00 GMST00 proc~gst00b->proc~gmst00 proc~nut00b NUT00B proc~ee00b->proc~nut00b proc~obl80 OBL80 proc~ee00b->proc~obl80 proc~ee00 EE00 proc~ee00b->proc~ee00 proc~pr00 PR00 proc~ee00b->proc~pr00 proc~gmst00->proc~anp proc~era00 ERA00 proc~gmst00->proc~era00 proc~eect00 EECT00 proc~ee00->proc~eect00 proc~era00->proc~anp proc~faom03 FAOM03 proc~eect00->proc~faom03 proc~falp03 FALP03 proc~eect00->proc~falp03 proc~fae03 FAE03 proc~eect00->proc~fae03 proc~fal03 FAL03 proc~eect00->proc~fal03 proc~faf03 FAF03 proc~eect00->proc~faf03 proc~fad03 FAD03 proc~eect00->proc~fad03 proc~fave03 FAVE03 proc~eect00->proc~fave03 proc~fapa03 FAPA03 proc~eect00->proc~fapa03

Contents

Source Code

GST00B

Source Code

    function GST00B ( uta, utb ) result(gast)

    implicit none

    real(wp),intent(in) :: uta !! UT1 as a 2-part Julian Date (Notes 1,2)
    real(wp),intent(in) :: utb !! UT1 as a 2-part Julian Date (Notes 1,2)
    real(wp) :: gast !! Greenwich apparent sidereal time (radians)

    gast = ANP ( GMST00 ( uta,utb, uta,utb ) + EE00B ( uta,utb ) )

    end function GST00B