APER Subroutine

  1. astro_module.f90
  2. astro_module
  3. APER

public subroutine APER(theta, astrom)

In the star-independent astrometry parameters, update only the Earth rotation angle, supplied by the caller explicitly.

Status: support routine.

Notes

  1. This routine exists to enable sidereal-tracking applications to avoid wasteful recomputation of the bulk of the astrometry parameters: only the Earth rotation is updated.

  2. For targets expressed as equinox based positions, such as classical geocentric apparent (RA,Dec), the supplied THETA can be Greenwich apparent sidereal time rather than Earth rotation angle.

  3. The routine APER13 can be used instead of the present routine, and starts from UT1 rather than ERA itself.

  4. This is one of several routines that inserts into the ASTROM array star-independent parameters needed for the chain of astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed.

    The various routines support different classes of observer and portions of the transformation chain:

        routines           observer        transformation

APCG APCG13    geocentric      ICRS <-> GCRS
APCI APCI13    terrestrial     ICRS <-> CIRS
APCO APCO13    terrestrial     ICRS <-> observed
APCS APCS13    space           ICRS <-> GCRS
APER APER13    terrestrial     update Earth rotation
APIO APIO13    terrestrial     CIRS <-> observed

    Those with names ending in "13" use contemporary SOFA models to compute the various ephemerides. The others accept ephemerides supplied by the caller.

    The transformation from ICRS to GCRS covers space motion, parallax, light deflection, and aberration. From GCRS to CIRS comprises frame bias and precession-nutation. From CIRS to observed takes account of Earth rotation, polar motion, diurnal aberration and parallax (unless subsumed into the ICRS <-> GCRS transformation), and atmospheric refraction.

History

  • IAU SOFA revision: 2013 September 25

Arguments

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

Earth rotation angle (radians, Note 2)
real(kind=wp), intent(inout), dimension(30):: astrom

star-independent astrometry parameters: * In: astrom(22): longitude + s' (radians) * Out: astrom(28): "local" Earth rotation angle (radians)

Called by

proc~~aper~~CalledByGraph proc~aper APER proc~apco APCO proc~apco->proc~aper proc~aper13 APER13 proc~aper13->proc~aper proc~apio APIO proc~apio->proc~aper proc~apco13 APCO13 proc~apco13->proc~apco proc~apio13 APIO13 proc~apio13->proc~apio 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

APER

Source Code

    subroutine APER ( theta, astrom )

    implicit none

    real(wp),intent(in) :: theta !! Earth rotation angle (radians, Note 2)
    real(wp),dimension(30),intent(inout) :: astrom !! star-independent astrometry parameters:
                                                   !! * In: astrom(22): longitude + s' (radians)
                                                   !! * Out: astrom(28): "local" Earth rotation angle (radians)

    astrom(28) = theta + astrom(22)

    end subroutine APER