EQEQ94 Function

  1. astro_module.f90
  2. astro_module
  3. EQEQ94

public function EQEQ94(date1, date2) result(eqe)

Equation of the equinoxes, IAU 1994 model.

Status: canonical model.

Notes

  1. The TDB date DATE1+DATE2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TDB)=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 result, which is in radians, operates in the following sense:

    Greenwich apparent ST = GMST + equation of the equinoxes

References

  • IAU Resolution C7, Recommendation 3 (1994)

  • Capitaine, N. & Gontier, A.-M., Astron.Astrophys., 275, 645-650 (1993)

History

  • IAU SOFA revision: 2017 October 12

Arguments

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

TDB date (Note 1)
real(kind=wp), intent(in) :: date2

TDB date (Note 1)

Return Value real(kind=wp)

equation of the equinoxes (Note 2)


Calls

proc~~eqeq94~~CallsGraph proc~eqeq94 EQEQ94 proc~anpm ANPM proc~eqeq94->proc~anpm proc~nut80 NUT80 proc~eqeq94->proc~nut80 proc~obl80 OBL80 proc~eqeq94->proc~obl80 proc~nut80->proc~anpm

Called by

proc~~eqeq94~~CalledByGraph proc~eqeq94 EQEQ94 proc~gst94 GST94 proc~gst94->proc~eqeq94

Contents

Source Code

EQEQ94

Source Code

    function EQEQ94 ( date1, date2 ) result(eqe)

    implicit none

    real(wp),intent(in) :: date1 !! TDB date (Note 1)
    real(wp),intent(in) :: date2 !! TDB date (Note 1)
    real(wp) :: eqe !! equation of the equinoxes (Note 2)

    real(wp) :: t, om, dpsi, deps, eps0

    !  Interval between fundamental epoch J2000.0 and given date (JC).
    t = ( ( date1-dj00 ) + date2 ) / djc

    !  Longitude of the mean ascending node of the lunar orbit on the
    !  ecliptic, measured from the mean equinox of date.
    om = ANPM( ( 450160.280_wp + ( -482890.539_wp + &
               ( 7.455_wp + 0.008_wp * t ) * t ) * t ) * das2r &
                 + mod(-5.0_wp*t,1.0_wp) * d2pi )

    !  Nutation components and mean obliquity.
    call NUT80 ( date1, date2, dpsi, deps )
    eps0 = OBL80 ( date1, date2 )

    !  Equation of the equinoxes.
    eqe = dpsi * cos(eps0) + das2r * ( 0.00264_wp * sin(om) + &
                                       0.000063_wp * sin(om+om))

    end function EQEQ94