OBL80 Function

  1. astro_module.f90
  2. astro_module
  3. OBL80

public function OBL80(date1, date2) result(obl)

Mean obliquity of the ecliptic, IAU 1980 model.

Status: canonical model.

Notes

  1. The 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 is the angle between the ecliptic and mean equator of date DATE1+DATE2.

Reference

  • Explanatory Supplement to the Astronomical Almanac, P. Kenneth Seidelmann (ed), University Science Books (1992), Expression 3.222-1 (p114).

History

  • IAU SOFA revision: 2009 December 15

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)

obliquity of the ecliptic (radians, Note 2)


Called by

proc~~obl80~~CalledByGraph proc~obl80 OBL80 proc~ee00a EE00A proc~ee00a->proc~obl80 proc~ee00b EE00B proc~ee00b->proc~obl80 proc~eqeq94 EQEQ94 proc~eqeq94->proc~obl80 proc~pn00 PN00 proc~pn00->proc~obl80 proc~nutm80 NUTM80 proc~nutm80->proc~obl80 proc~pn00a PN00A proc~pn00a->proc~pn00 proc~gst94 GST94 proc~gst94->proc~eqeq94 proc~pnm80 PNM80 proc~pnm80->proc~nutm80 proc~gst00a GST00A proc~gst00a->proc~ee00a proc~pn00b PN00B proc~pn00b->proc~pn00 proc~gst00b GST00B proc~gst00b->proc~ee00b proc~c2tpe C2TPE proc~c2tpe->proc~pn00 proc~pnm00a PNM00A proc~pnm00a->proc~pn00a proc~num00a NUM00A proc~num00a->proc~pn00a proc~num00b NUM00B proc~num00b->proc~pn00b proc~pnm00b PNM00B proc~pnm00b->proc~pn00b proc~xys00a XYS00A proc~xys00a->proc~pnm00a proc~s00a S00A proc~s00a->proc~pnm00a proc~c2i00b C2I00B proc~c2i00b->proc~pnm00b proc~c2i00a C2I00A proc~c2i00a->proc~pnm00a proc~s00b S00B proc~s00b->proc~pnm00b proc~xys00b XYS00B proc~xys00b->proc~pnm00b proc~c2t00b C2T00B proc~c2t00b->proc~c2i00b proc~c2t00a C2T00A proc~c2t00a->proc~c2i00a

Contents

Source Code

OBL80

Source Code

    function OBL80 ( date1, date2 ) result(obl)

    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) :: obl !! obliquity of the ecliptic (radians, Note 2)

    real(wp) :: t

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

    !  Mean obliquity of date.
    obl = das2r * ( 84381.448_wp + &
                    ( -46.8150_wp + &
                     ( -0.00059_wp + &
                        0.001813_wp * t ) * t ) * t )

    end function OBL80