EORS Function

  1. astro_module.f90
  2. astro_module
  3. EORS

public function EORS(rnpb, s) result(res)

Equation of the origins, given the classical NPB matrix and the quantity s.

Status: support routine.

Notes

  1. The equation of the origins is the distance between the true equinox and the celestial intermediate origin and, equivalently, the difference between Earth rotation angle and Greenwich apparent sidereal time (ERA-GST). It comprises the precession (since J2000.0) in right ascension plus the equation of the equinoxes (including the small correction terms).

  2. The algorithm is from Wallace & Capitaine (2006).

References

  • Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855

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

History

  • IAU SOFA revision: 2008 February 24

Arguments

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

classical nutation x precession x bias matrix
real(kind=wp), intent(in) :: s

the quantity s (the CIO locator)

Return Value real(kind=wp)

the equation of the origins in radians.


Called by

proc~~eors~~CalledByGraph proc~eors EORS proc~gst06 GST06 proc~gst06->proc~eors proc~apci13 APCI13 proc~apci13->proc~eors proc~eo06a EO06A proc~eo06a->proc~eors proc~apco13 APCO13 proc~apco13->proc~eors proc~gst06a GST06A proc~gst06a->proc~gst06 proc~atic13 ATIC13 proc~atic13->proc~apci13 proc~atci13 ATCI13 proc~atci13->proc~apci13 proc~atco13 ATCO13 proc~atco13->proc~apco13 proc~atoc13 ATOC13 proc~atoc13->proc~apco13 proc~ee06a EE06A proc~ee06a->proc~gst06a

Contents

Source Code

EORS

Source Code

    function EORS ( rnpb, s ) result(res)

    implicit none

    real(wp),dimension(3,3),intent(in) :: rnpb !! classical nutation x precession x bias matrix
    real(wp),intent(in) :: s !! the quantity s (the CIO locator)
    real(wp) :: res !! the equation of the origins in radians.

    real(wp) :: x, ax, xs, ys, zs, p, q

    !  Evaluate Wallace & Capitaine (2006) expression (16).
    x = rnpb(3,1)
    ax = x / ( 1.0_wp + rnpb(3,3) )
    xs = 1.0_wp - ax*x
    ys = -ax*rnpb(3,2)
    zs = -x
    p = rnpb(1,1)*xs + rnpb(1,2)*ys + rnpb(1,3)*zs
    q = rnpb(2,1)*xs + rnpb(2,2)*ys + rnpb(2,3)*zs
    if ( p/=0.0_wp .or. q/=0.0_wp ) then
       res = s - atan2 ( q, p )
    else
       res = s
    end if

    end function EORS