ab¶

erfa.ab(pnat, v, s, bm1)[source]¶

Apply aberration to transform natural direction into proper direction.

Parameters:

pnatdouble array
vdouble array
sdouble array
bm1double array

Returns:

pprdouble array

Notes

Wraps ERFA function eraAb. The ERFA documentation is:

- - - - - -
 e r a A b
- - - - - -

Apply aberration to transform natural direction into proper
direction.

Given:
  pnat    double[3]   natural direction to the source (unit vector)
  v       double[3]   observer barycentric velocity in units of c
  s       double      distance between the Sun and the observer (au)
  bm1     double      sqrt(1-|v|^2): reciprocal of Lorenz factor

Returned:
  ppr     double[3]   proper direction to source (unit vector)

Notes:

1) The algorithm is based on Expr. (7.40) in the Explanatory
   Supplement (Urban & Seidelmann 2013), but with the following
   changes:

   o  Rigorous rather than approximate normalization is applied.

   o  The gravitational potential term from Expr. (7) in
      Klioner (2003) is added, taking into account only the Sun's
      contribution.  This has a maximum effect of about
      0.4 microarcsecond.

2) In almost all cases, the maximum accuracy will be limited by the
   supplied velocity.  For example, if the ERFA eraEpv00 function is
   used, errors of up to 5 microarcseconds could occur.

References:

   Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to
   the Astronomical Almanac, 3rd ed., University Science Books
   (2013).

   Klioner, Sergei A., "A practical relativistic model for micro-
   arcsecond astrometry in space", Astr. J. 125, 1580-1597 (2003).

Called:
   eraPdp       scalar product of two p-vectors

This revision:   2021 February 24

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

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