GST00A Function

  1. astro_module.f90
  2. astro_module
  3. GST00A

public function GST00A(uta, utb, tta, ttb) result(gast)

Greenwich Apparent Sidereal Time (consistent with IAU 2000 resolutions).

Status: canonical model.

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=2450123.7 could be expressed in any of these ways, among others:

        Part A         Part B

 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 (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 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. 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 result.

  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., 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)
real(kind=wp), intent(in) :: tta

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

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

Return Value real(kind=wp)

Greenwich apparent sidereal time (radians)


Calls

proc~~gst00a~~CallsGraph proc~gst00a GST00A proc~anp ANP proc~gst00a->proc~anp proc~gmst00 GMST00 proc~gst00a->proc~gmst00 proc~ee00a EE00A proc~gst00a->proc~ee00a proc~gmst00->proc~anp proc~era00 ERA00 proc~gmst00->proc~era00 proc~nut00a NUT00A proc~ee00a->proc~nut00a proc~obl80 OBL80 proc~ee00a->proc~obl80 proc~ee00 EE00 proc~ee00a->proc~ee00 proc~pr00 PR00 proc~ee00a->proc~pr00 proc~faom03 FAOM03 proc~nut00a->proc~faom03 proc~faju03 FAJU03 proc~nut00a->proc~faju03 proc~fasa03 FASA03 proc~nut00a->proc~fasa03 proc~fae03 FAE03 proc~nut00a->proc~fae03 proc~fame03 FAME03 proc~nut00a->proc~fame03 proc~fal03 FAL03 proc~nut00a->proc~fal03 proc~fapa03 FAPA03 proc~nut00a->proc~fapa03 proc~faf03 FAF03 proc~nut00a->proc~faf03 proc~fave03 FAVE03 proc~nut00a->proc~fave03 proc~fama03 FAMA03 proc~nut00a->proc~fama03 proc~faur03 FAUR03 proc~nut00a->proc~faur03 proc~eect00 EECT00 proc~ee00->proc~eect00 proc~era00->proc~anp proc~eect00->proc~faom03 proc~eect00->proc~fae03 proc~eect00->proc~fal03 proc~eect00->proc~fapa03 proc~eect00->proc~faf03 proc~eect00->proc~fave03 proc~falp03 FALP03 proc~eect00->proc~falp03 proc~fad03 FAD03 proc~eect00->proc~fad03

Contents

Source Code

GST00A

Source Code

    function GST00A ( uta, utb, tta, ttb ) 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),intent(in) :: tta !! TT as a 2-part Julian Date (Notes 1,2)
    real(wp),intent(in) :: ttb !! TT as a 2-part Julian Date (Notes 1,2)
    real(wp) :: gast !! Greenwich apparent sidereal time (radians)

    gast = ANP ( GMST00 ( uta,utb, tta,ttb ) + EE00A ( tta,ttb ) )

    end function GST00A