EQEC06 Subroutine

  1. astro_module.f90
  2. astro_module
  3. EQEC06

public subroutine EQEC06(date1, date2, dr, dd, dl, db)

Transformation from ICRS equatorial coordinates to ecliptic coordinates (mean equinox and ecliptic of date) using IAU 2006 precession 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. No assumptions are made about whether the coordinates represent starlight and embody astrometric effects such as parallax or aberration.

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

History

  • IAU SOFA revision: 2016 February 9

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)
real(kind=wp), intent(in) :: dr

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

ICRS declination (radians)
real(kind=wp), intent(out) :: dl

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

ecliptic latitude (radians)

Calls

proc~~eqec06~~CallsGraph proc~eqec06 EQEC06 proc~c2s C2S proc~eqec06->proc~c2s proc~anpm ANPM proc~eqec06->proc~anpm proc~rxp RXP proc~eqec06->proc~rxp proc~ecm06 ECM06 proc~eqec06->proc~ecm06 proc~s2c S2C proc~eqec06->proc~s2c proc~anp ANP proc~eqec06->proc~anp proc~obl06 OBL06 proc~ecm06->proc~obl06 proc~rx RX proc~ecm06->proc~rx proc~pmat06 PMAT06 proc~ecm06->proc~pmat06 proc~rxr RXR proc~ecm06->proc~rxr proc~ir IR proc~ecm06->proc~ir proc~pfw06 PFW06 proc~pmat06->proc~pfw06 proc~fw2m FW2M proc~pmat06->proc~fw2m proc~pfw06->proc~obl06 proc~fw2m->proc~rx proc~fw2m->proc~ir proc~rz RZ proc~fw2m->proc~rz

Contents

Source Code

EQEC06

Source Code

    subroutine EQEC06 ( date1, date2, dr, dd, dl, db )

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

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

    !  Spherical to Cartesian.
    call S2C ( dr, dd, v1 )

    !  Rotation matrix, ICRS equatorial to ecliptic.
    call ECM06 ( date1, date2, rm )

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

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

    !  Express in conventional ranges.
    dl = ANP ( a )
    db = ANPM ( b )

    end subroutine EQEC06