GST06 Function

  1. astro_module.f90
  2. astro_module
  3. GST06

public function GST06(uta, utb, tta, ttb, rnpb) result(gast)

Greenwich apparent sidereal time, IAU 2006, given the NPB matrix.

Status: support routine.

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. Although the routine uses the IAU 2006 series for s+XY/2, it is otherwise independent of the precession-nutation model and can in practice be used with any equinox-based NPB matrix.

  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: 2008 January 2

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)
real(kind=wp), intent(in), dimension(3,3):: rnpb

nutation x precession x bias matrix

Return Value real(kind=wp)

Greenwich apparent sidereal time (radians)


Calls

proc~~gst06~~CallsGraph proc~gst06 GST06 proc~eors EORS proc~gst06->proc~eors proc~s06 S06 proc~gst06->proc~s06 proc~era00 ERA00 proc~gst06->proc~era00 proc~bpn2xy BPN2XY proc~gst06->proc~bpn2xy proc~anp ANP proc~gst06->proc~anp 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~era00->proc~anp

Called by

proc~~gst06~~CalledByGraph proc~gst06 GST06 proc~gst06a GST06A proc~gst06a->proc~gst06 proc~ee06a EE06A proc~ee06a->proc~gst06a

Contents

Source Code

GST06

Source Code

    function GST06 ( uta, utb, tta, ttb, rnpb ) 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),dimension(3,3),intent(in) :: rnpb !! nutation x precession x bias matrix
    real(wp) :: gast !! Greenwich apparent sidereal time (radians)

    real(wp) :: x, y, s

    !  Extract CIP coordinates.
    call BPN2XY ( rnpb, x, y )

    !  The CIO locator, s.
    s = S06 ( tta, ttb, x, y )

    !  Greenwich apparent sidereal time.
    gast = ANP ( ERA00 ( uta, utb ) - EORS ( rnpb, s ) )

    end function GST06