Py ERFA:docs

- Index
- Modules

### Navigation

- next »
- « previous |
- PyERFA v2.0.0.1 »
- erfa Package »
- ab

# ab

erfa.ab(pnat, v, s, bm1)

  Apply aberration to transform natural direction into proper direction.

  Parameters
    pnat double array
    v double array
    s double array
    bm1 double array
  Returns
    ppr double 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) 2013-2021, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.