S00A Function

  1. astro_module.f90
  2. astro_module
  3. S00A

public function S00A(date1, date2) result(s)

The CIO locator s, positioning the Celestial Intermediate Origin on the equator of the Celestial Intermediate Pole, using the IAU 2000A precession-nutation model.

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 CIO locator s is the difference between the right ascensions of the same point in two systems. The two systems are the GCRS and the CIP,CIO, and the point is the ascending node of the CIP equator. The CIO locator s remains a small fraction of 1 arcsecond throughout 1900-2100.

  3. The series used to compute s is in fact for s+XY/2, where X and Y are the x and y components of the CIP unit vector; this series is more compact than a direct series for s would be. The present routine uses the full IAU 2000A nutation model when predicting the CIP position. Faster results, with no significant loss of accuracy, can be obtained via the routine S00B, which uses instead the IAU 2000B truncated model.

References

  • Capitaine, N., Chapront, J., Lambert, S. and Wallace, P., "Expressions for the Celestial Intermediate Pole and Celestial Ephemeris Origin consistent with the IAU 2000A precession-nutation model", Astron.Astrophys. 400, 1145-1154 (2003)

  • n.b. The celestial ephemeris origin (CEO) was renamed "celestial intermediate origin" (CIO) by IAU 2006 Resolution 2.

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

History

  • IAU SOFA revision: 2010 January 18

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 CIO locator s in radians (Note 2)


Calls

proc~~s00a~~CallsGraph proc~s00a S00A proc~pnm00a PNM00A proc~s00a->proc~pnm00a proc~s00 S00 proc~s00a->proc~s00 proc~bpn2xy BPN2XY proc~s00a->proc~bpn2xy proc~pn00a PN00A proc~pnm00a->proc~pn00a proc~faom03 FAOM03 proc~s00->proc~faom03 proc~falp03 FALP03 proc~s00->proc~falp03 proc~fae03 FAE03 proc~s00->proc~fae03 proc~fal03 FAL03 proc~s00->proc~fal03 proc~faf03 FAF03 proc~s00->proc~faf03 proc~fad03 FAD03 proc~s00->proc~fad03 proc~fave03 FAVE03 proc~s00->proc~fave03 proc~fapa03 FAPA03 proc~s00->proc~fapa03 proc~nut00a NUT00A proc~pn00a->proc~nut00a proc~pn00 PN00 proc~pn00a->proc~pn00 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 proc~obl80 OBL80 proc~pn00->proc~obl80 proc~numat NUMAT proc~pn00->proc~numat proc~bp00 BP00 proc~pn00->proc~bp00 proc~pr00 PR00 proc~pn00->proc~pr00 proc~rxr RXR proc~pn00->proc~rxr proc~rx RX proc~numat->proc~rx proc~ir IR proc~numat->proc~ir proc~rz RZ proc~numat->proc~rz proc~bp00->proc~pr00 proc~bp00->proc~rxr proc~bp00->proc~rx proc~ry RY proc~bp00->proc~ry proc~bp00->proc~ir proc~bp00->proc~rz proc~bi00 BI00 proc~bp00->proc~bi00

Contents

Source Code

S00A

Source Code

    function S00A ( date1, date2 ) result(s)

    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) :: s !! the CIO locator s in radians (Note 2)

    real(wp) :: rbpn(3,3), x, y

    !  Bias-precession-nutation-matrix, IAU 2000A.
    call PNM00A ( date1, date2, rbpn )

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

    !  Compute the CIO locator s, given the CIP coordinates.
    s = S00 ( date1, date2, x, y )

    end function S00A