fk425¶
- erfa.fk425(r1950, d1950, dr1950, dd1950, p1950, v1950)[source]¶
Convert B1950.0 FK4 star catalog data to J2000.0 FK5.
- Parameters:
- r1950double array
- d1950double array
- dr1950double array
- dd1950double array
- p1950double array
- v1950double array
- Returns:
- r2000double array
- d2000double array
- dr2000double array
- dd2000double array
- p2000double array
- v2000double array
Notes
Wraps ERFA function
eraFk425
. The ERFA documentation is:- - - - - - - - - e r a F k 4 2 5 - - - - - - - - - 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. This revision: 2023 March 20 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.