LTECEQ Subroutine

  1. astro_module.f90
  2. astro_module
  3. LTECEQ

public subroutine LTECEQ(epj, dl, db, dr, dd)

Transformation from ecliptic coordinates (mean equinox and ecliptic of date) to ICRS RA,Dec, using a long-term precession model.

Status: support routine.

  1. No assumptions are made about whether the coordinates represent starlight and embody astrometric effects such as parallax or aberration.

  2. The transformation is approximately that from ecliptic longitude and latitude (mean equinox and ecliptic of date) to mean J2000.0 right ascension and declination, with only frame bias (always less than 25 mas) to disturb this classical picture.

  3. The Vondrak et al. (2011, 2012) 400 millennia precession model agrees with the IAU 2006 precession at J2000.0 and stays within 100 microarcseconds during the 20th and 21st centuries. It is accurate to a few arcseconds throughout the historical period, worsening to a few tenths of a degree at the end of the +/- 200,000 year time span.

References

  • Vondrak, J., Capitaine, N. and Wallace, P., 2011, New precession expressions, valid for long time intervals, Astron.Astrophys. 534, A22

  • Vondrak, J., Capitaine, N. and Wallace, P., 2012, New precession expressions, valid for long time intervals (Corrigendum), Astron.Astrophys. 541, C1

History

  • IAU SOFA revision: 2016 February 9

Arguments

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

Julian epoch (TT)
real(kind=wp), intent(in) :: dl

ecliptic longitude (radians)
real(kind=wp), intent(in) :: db

ecliptic latitude (radians)
real(kind=wp), intent(out) :: dr

ICRS right ascension (radians)
real(kind=wp), intent(out) :: dd

ICRS declination (radians)

Calls

proc~~lteceq~~CallsGraph proc~lteceq LTECEQ proc~c2s C2S proc~lteceq->proc~c2s proc~anpm ANPM proc~lteceq->proc~anpm proc~ltecm LTECM proc~lteceq->proc~ltecm proc~anp ANP proc~lteceq->proc~anp proc~s2c S2C proc~lteceq->proc~s2c proc~trxp TRXP proc~lteceq->proc~trxp proc~ltpecl LTPECL proc~ltecm->proc~ltpecl proc~ltpequ LTPEQU proc~ltecm->proc~ltpequ proc~pxp PXP proc~ltecm->proc~pxp proc~rxp RXP proc~trxp->proc~rxp proc~tr TR proc~trxp->proc~tr

Contents

Source Code

LTECEQ

Source Code

    subroutine LTECEQ ( epj, dl, db, dr, dd )

    implicit none

    real(wp),intent(in) :: epj !! Julian epoch (TT)
    real(wp),intent(in) :: dl !! ecliptic longitude (radians)
    real(wp),intent(in) :: db !! ecliptic latitude (radians)
    real(wp),intent(out) :: dr !! ICRS right ascension (radians)
    real(wp),intent(out) :: dd !! ICRS declination (radians)

    real(wp) :: rm(3,3), v1(3), v2(3), a, b

    !  Spherical to Cartesian.
    call S2C ( dl, db, v1 )

    !  Rotation matrix, ICRS equatorial to ecliptic.
    call LTECM ( epj, rm )

    !  The transformation from ecliptic to ICRS.
    call TRXP ( rm, v1, v2 )

    !  Cartesian to spherical.
    call C2S ( v2, a, b )

    !  Express in conventional ranges.
    dr = ANP ( a )
    dd = ANPM ( b )

    end subroutine LTECEQ