EO06A Function

  1. astro_module.f90
  2. astro_module
  3. EO06A

public function EO06A(date1, date2) result(res)

Equation of the origins, IAU 2006 precession and IAU 2000A nutation.

Status: support routine.

Notes

  1. The TT date DATE1+DATE2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=2450123.7 could be expressed in any of these ways, among others:

        DATE1          DATE2

 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 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date & time methods are both good compromises between resolution and convenience.

  2. 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).

References

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

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

History

  • IAU SOFA revision: 2007 February 13

Arguments

TypeIntentOptionalAttributesName
real(kind=wp), intent(in) :: date1

TT as a 2-part Julian Date (Note 1)
real(kind=wp), intent(in) :: date2

TT as a 2-part Julian Date (Note 1)

Return Value real(kind=wp)

equation of the origins in radians


Calls

proc~~eo06a~~CallsGraph proc~eo06a EO06A proc~pnm06a PNM06A proc~eo06a->proc~pnm06a proc~eors EORS proc~eo06a->proc~eors proc~bpn2xy BPN2XY proc~eo06a->proc~bpn2xy proc~s06 S06 proc~eo06a->proc~s06 proc~pfw06 PFW06 proc~pnm06a->proc~pfw06 proc~nut06a NUT06A proc~pnm06a->proc~nut06a proc~fw2m FW2M proc~pnm06a->proc~fw2m proc~falp03 FALP03 proc~s06->proc~falp03 proc~faom03 FAOM03 proc~s06->proc~faom03 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~obl06 OBL06 proc~pfw06->proc~obl06 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~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

Contents

Source Code

EO06A

Source Code

    function EO06A ( date1, date2 ) result(res)

    implicit none

    real(wp),intent(in) :: date1 !! TT as a 2-part Julian Date (Note 1)
    real(wp),intent(in) :: date2 !! TT as a 2-part Julian Date (Note 1)
    real(wp) :: res !! equation of the origins in radians

    real(wp) :: r(3,3), x, y, s
    !  Classical nutation x precession x bias matrix.
    call PNM06A ( date1, date2, r )

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

    !  The CIO locator, s.
    s = S06 ( date1, date2, x, y )

    !  Solve for the EO.
    res = EORS ( r, s )

    end function EO06A