lteqec¶
- erfa.lteqec(epj, dr, dd)[source]¶
Transformation from ICRS RA,Dec to ecliptic coordinates (mean equinox and ecliptic of date), using a long-term precession model.
- Parameters:
- epjdouble array
- drdouble array
- dddouble array
- Returns:
- dldouble array
- dbdouble array
Notes
Wraps ERFA function
eraLteqec
. The ERFA documentation is:- - - - - - - - - - e r a L t e q e c - - - - - - - - - - Transformation from ICRS RA,Dec to ecliptic coordinates (mean equinox and ecliptic of date), using a long-term precession model. Given: epj double Julian epoch (TT) dr,dd double ICRS right ascension and declination (radians) Returned: dl,db double ecliptic longitude and latitude (radians) 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 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. 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. Called: eraS2c spherical coordinates to unit vector eraLtecm J2000.0 to ecliptic rotation matrix, long term 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 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 This revision: 2023 March 18 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.