eqec06¶

erfa.eqec06(date1, date2, dr, dd)[source]¶

Transformation from ICRS equatorial coordinates to ecliptic coordinates (mean equinox and ecliptic of date) using IAU 2006 precession model.

Parameters:

date1double array
date2double array
drdouble array
dddouble array

Returns:

dldouble array
dbdouble array

Notes

Wraps ERFA function eraEqec06. The ERFA documentation is:

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 e r a E q e c 0 6
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Transformation from ICRS equatorial coordinates to ecliptic
coordinates (mean equinox and ecliptic of date) using IAU 2006
precession model.

Given:
   date1,date2 double TT as a 2-part Julian date (Note 1)
   dr,dd       double ICRS right ascension and declination (radians)

Returned:
   dl,db       double ecliptic longitude and latitude (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 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.

Called:
   eraS2c       spherical coordinates to unit vector
   eraEcm06     J2000.0 to ecliptic rotation matrix, IAU 2006
   eraRxp       product 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.

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eqec06¶