GST06A Function

  1. astro_module.f90
  2. astro_module
  3. GST06A

public function GST06A(uta, utb, tta, ttb) result(gast)

Greenwich apparent sidereal time (consistent with IAU 2000 and 2006 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 2000/2006 resolutions and must be used only in conjunction with IAU 2006 precession and IAU 2000A nutation.

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

Reference

 Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981

History

  • IAU SOFA revision: 2010 March 5

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~~gst06a~~CallsGraph proc~gst06a GST06A proc~pnm06a PNM06A proc~gst06a->proc~pnm06a proc~gst06 GST06 proc~gst06a->proc~gst06 proc~pfw06 PFW06 proc~pnm06a->proc~pfw06 proc~nut06a NUT06A proc~pnm06a->proc~nut06a proc~fw2m FW2M proc~pnm06a->proc~fw2m proc~eors EORS proc~gst06->proc~eors proc~s06 S06 proc~gst06->proc~s06 proc~bpn2xy BPN2XY proc~gst06->proc~bpn2xy proc~era00 ERA00 proc~gst06->proc~era00 proc~anp ANP proc~gst06->proc~anp proc~obl06 OBL06 proc~pfw06->proc~obl06 proc~faom03 FAOM03 proc~s06->proc~faom03 proc~falp03 FALP03 proc~s06->proc~falp03 proc~fae03 FAE03 proc~s06->proc~fae03 proc~fal03 FAL03 proc~s06->proc~fal03 proc~faf03 FAF03 proc~s06->proc~faf03 proc~fad03 FAD03 proc~s06->proc~fad03 proc~fave03 FAVE03 proc~s06->proc~fave03 proc~fapa03 FAPA03 proc~s06->proc~fapa03 proc~nut00a NUT00A proc~nut06a->proc~nut00a proc~rx RX proc~fw2m->proc~rx proc~ir IR proc~fw2m->proc~ir proc~rz RZ proc~fw2m->proc~rz proc~era00->proc~anp proc~nut00a->proc~faom03 proc~nut00a->proc~fae03 proc~nut00a->proc~fal03 proc~nut00a->proc~faf03 proc~nut00a->proc~fave03 proc~nut00a->proc~fapa03 proc~fame03 FAME03 proc~nut00a->proc~fame03 proc~fasa03 FASA03 proc~nut00a->proc~fasa03 proc~faju03 FAJU03 proc~nut00a->proc~faju03 proc~fama03 FAMA03 proc~nut00a->proc~fama03 proc~faur03 FAUR03 proc~nut00a->proc~faur03

Called by

proc~~gst06a~~CalledByGraph proc~gst06a GST06A proc~ee06a EE06A proc~ee06a->proc~gst06a

Contents

Source Code

GST06A

Source Code

    function GST06A ( 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)

    real(wp) :: rnpb(3,3)

    !  Classical nutation x precession x bias matrix, IAU 2000A/2006.
    call PNM06A ( tta, ttb, rnpb )

    !  Greenwich apparent sidereal time.
    gast = GST06 ( uta, utb, tta, ttb, rnpb )

    end function GST06A