ltecm¶
- erfa.ltecm(epj)[source]¶
ICRS equatorial to ecliptic rotation matrix, long-term.
- Parameters:
- epjdouble array
- Returns:
- rmdouble array
Notes
Wraps ERFA function
eraLtecm
. The ERFA documentation is:- - - - - - - - - e r a L t e c m - - - - - - - - - ICRS equatorial to ecliptic rotation matrix, long-term. Given: epj double Julian epoch (TT) Returned: rm double[3][3] ICRS to ecliptic rotation matrix Notes: 1) The matrix is in the sense E_ep = rm x P_ICRS, where P_ICRS is a vector with respect to ICRS right ascension and declination axes and E_ep is the same vector with respect to the (inertial) ecliptic and equinox of epoch epj. 2) P_ICRS is a free vector, merely a direction, typically of unit magnitude, and not bound to any particular spatial origin, such as the Earth, Sun or SSB. No assumptions are made about whether it represents starlight and embodies astrometric effects such as parallax or aberration. The transformation is approximately that between mean J2000.0 right ascension and declination and ecliptic longitude and latitude, 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: eraLtpequ equator pole, long term eraLtpecl ecliptic pole, long term eraPxp vector product eraPn normalize vector 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: 2021 May 11 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.