Py ERFA:docs

- Index
- Modules

### Navigation

- next »
- « previous |
- PyERFA v2.0.1.5 »
- erfa Package »
- eceq06

# eceq06

erfa.eceq06(date1, date2, dl, db)

  Transformation from ecliptic coordinates (mean equinox and ecliptic of date) to ICRS RA,Dec, using the IAU 2006 precession model.

  Parameters:
    date1 double array
    date2 double array
    dl double array
    db double array
  Returns:
    dr double array
    dd double array

  Notes

  Wraps ERFA function `eraEceq06`. The ERFA documentation is:

      - - - - - - - - - -
       e r a E c e q 0 6
      - - - - - - - - - -

      Transformation from ecliptic coordinates (mean equinox and ecliptic
      of date) to ICRS RA,Dec, using the IAU 2006 precession model.

      Given:
         date1,date2 double TT as a 2-part Julian date (Note 1)
         dl,db       double ecliptic longitude and latitude (radians)

      Returned:
         dr,dd       double ICRS right ascension and declination (radians)

      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

             2450123.7           0.0       (JD method)
             2451545.0       -1421.3       (J2000 method)
             2400000.5       50123.2       (MJD method)
             2450123.5           0.2       (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 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.

      Called:
         eraS2c       spherical coordinates to unit vector
         eraEcm06     J2000.0 to ecliptic rotation matrix, IAU 2006
         eraTrxp      product of transpose of r-matrix and p-vector
         eraC2s       unit vector to spherical coordinates
         eraAnp       normalize angle into range 0 to 2pi
         eraAnpm      normalize angle into range +/- pi

      This revision:  2021 May 11

      Copyright (C) 2013-2023, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.