fk425

erfa.fk425(r1950, d1950, dr1950, dd1950, p1950, v1950)[source]

Wrapper for ERFA function eraFk425.

Parameters

r1950 : double array

d1950 : double array

dr1950 : double array

dd1950 : double array

p1950 : double array

v1950 : double array

Returns

r2000 : double array

d2000 : double array

dr2000 : double array

dd2000 : double array

p2000 : double array

v2000 : double array

Notes

The ERFA documentation is below.

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  e r a F k 4 2 5
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 Convert B1950.0 FK4 star catalog data to J2000.0 FK5.

 This function converts a star's catalog data from the old FK4
(Bessel-Newcomb) system to the later IAU 1976 FK5 (Fricke) system.

 Given: (all B1950.0, FK4)
    r1950,d1950    double   B1950.0 RA,Dec (rad)
    dr1950,dd1950  double   B1950.0 proper motions (rad/trop.yr)
    p1950          double   parallax (arcsec)
    v1950          double   radial velocity (km/s, +ve = moving away)

 Returned: (all J2000.0, FK5)
    r2000,d2000    double   J2000.0 RA,Dec (rad)
    dr2000,dd2000  double   J2000.0 proper motions (rad/Jul.yr)
    p2000          double   parallax (arcsec)
    v2000          double   radial velocity (km/s, +ve = moving away)

 Notes:

 1) The proper motions in RA are dRA/dt rather than cos(Dec)*dRA/dt,
    and are per year rather than per century.

 2) The conversion is somewhat complicated, for several reasons:

    . Change of standard epoch from B1950.0 to J2000.0.

    . An intermediate transition date of 1984 January 1.0 TT.

    . A change of precession model.

    . Change of time unit for proper motion (tropical to Julian).

    . FK4 positions include the E-terms of aberration, to simplify
      the hand computation of annual aberration.  FK5 positions
      assume a rigorous aberration computation based on the Earth's
      barycentric velocity.

    . The E-terms also affect proper motions, and in particular cause
      objects at large distances to exhibit fictitious proper
      motions.

    The algorithm is based on Smith et al. (1989) and Yallop et al.
    (1989), which presented a matrix method due to Standish (1982) as
    developed by Aoki et al. (1983), using Kinoshita's development of
    Andoyer's post-Newcomb precession.  The numerical constants from
    Seidelmann (1992) are used canonically.

 3) Conversion from B1950.0 FK4 to J2000.0 FK5 only is provided for.
    Conversions for different epochs and equinoxes would require
    additional treatment for precession, proper motion and E-terms.

 4) In the FK4 catalog the proper motions of stars within 10 degrees
    of the poles do not embody differential E-terms effects and
    should, strictly speaking, be handled in a different manner from
    stars outside these regions.  However, given the general lack of
    homogeneity of the star data available for routine astrometry,
    the difficulties of handling positions that may have been
    determined from astrometric fields spanning the polar and non-
    polar regions, the likelihood that the differential E-terms
    effect was not taken into account when allowing for proper motion
    in past astrometry, and the undesirability of a discontinuity in
    the algorithm, the decision has been made in this ERFA algorithm
    to include the effects of differential E-terms on the proper
    motions for all stars, whether polar or not.  At epoch J2000.0,
    and measuring "on the sky" rather than in terms of RA change, the
    errors resulting from this simplification are less than
    1 milliarcsecond in position and 1 milliarcsecond per century in
    proper motion.

 Called:
    eraAnp       normalize angle into range 0 to 2pi
    eraPv2s      pv-vector to spherical coordinates
    eraPdp       scalar product of two p-vectors
    eraPvmpv     pv-vector minus pv_vector
    eraPvppv     pv-vector plus pv_vector
    eraS2pv      spherical coordinates to pv-vector
    eraSxp       multiply p-vector by scalar

 References:

    Aoki, S. et al., 1983, "Conversion matrix of epoch B1950.0
    FK4-based positions of stars to epoch J2000.0 positions in
    accordance with the new IAU resolutions".  Astron.Astrophys.
    128, 263-267.

    Seidelmann, P.K. (ed), 1992, "Explanatory Supplement to the
    Astronomical Almanac", ISBN 0-935702-68-7.

    Smith, C.A. et al., 1989, "The transformation of astrometric
    catalog systems to the equinox J2000.0".  Astron.J. 97, 265.

    Standish, E.M., 1982, "Conversion of positions and proper motions
    from B1950.0 to the IAU system at J2000.0".  Astron.Astrophys.,
    115, 1, 20-22.

    Yallop, B.D. et al., 1989, "Transformation of mean star places
    from FK4 B1950.0 to FK5 J2000.0 using matrices in 6-space".
    Astron.J. 97, 274.

 Copyright (C) 2013-2019, NumFOCUS Foundation.
 Derived, with permission, from the SOFA library.  See notes at end of file.