SP00 Function

  1. astro_module.f90
  2. astro_module
  3. SP00

public function SP00(date1, date2) result(sp)

The TIO locator s', positioning the Terrestrial Intermediate Origin on the equator of the Celestial Intermediate Pole.

Status: canonical model.

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 TIO locator s' is obtained from polar motion observations by numerical integration, and so is in essence unpredictable. However, it is dominated by a secular drift of about 47 microarcseconds per century, which is the approximation evaluated by the present routine.

Reference

  • McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), IERS Technical Note No. 32, BKG (2004)

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)

the TIO locator s' in radians (Note 2)


Called by

proc~~sp00~~CalledByGraph proc~sp00 SP00 proc~apco13 APCO13 proc~apco13->proc~sp00 proc~c2t00a C2T00A proc~c2t00a->proc~sp00 proc~c2txy C2TXY proc~c2txy->proc~sp00 proc~c2tpe C2TPE proc~c2tpe->proc~sp00 proc~apio13 APIO13 proc~apio13->proc~sp00 proc~c2t06a C2T06A proc~c2t06a->proc~sp00 proc~atco13 ATCO13 proc~atco13->proc~apco13 proc~atoi13 ATOI13 proc~atoi13->proc~apio13 proc~atio13 ATIO13 proc~atio13->proc~apio13 proc~atoc13 ATOC13 proc~atoc13->proc~apco13

Contents

Source Code

SP00

Source Code

    function SP00 ( date1, date2 ) result(sp)

    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) :: sp !! the TIO locator s' in radians (Note 2)

    !  Time since J2000.0, in Julian centuries
    real(wp) :: t

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

    !  Approximate s'.
    sp = -47.0e-6_wp * t * das2r

    end function SP00