vec = ERFA.ltpecl(epj)Long-term precession of the ecliptic.
epj double Julian epoch (TT)
vec double[3] ecliptic pole unit vector
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The returned vector is with respect to the J2000.0 mean equator and equinox.
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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.
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) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.