fk54z¶
- erfa.fk54z(r2000, d2000, bepoch)[source]¶
Convert a J2000.0 FK5 star position to B1950.0 FK4, assuming zero proper motion in FK5 and parallax.
- Parameters:
- r2000double array
- d2000double array
- bepochdouble array
- Returns:
- r1950double array
- d1950double array
- dr1950double array
- dd1950double array
Notes
Wraps ERFA function
eraFk54z
. The ERFA documentation is:- - - - - - - - - e r a F k 5 4 z - - - - - - - - - Convert a J2000.0 FK5 star position to B1950.0 FK4, assuming zero proper motion in FK5 and parallax. Given: r2000,d2000 double J2000.0 FK5 RA,Dec (rad) bepoch double Besselian epoch (e.g. 1950.0) Returned: r1950,d1950 double B1950.0 FK4 RA,Dec (rad) at epoch BEPOCH dr1950,dd1950 double B1950.0 FK4 proper motions (rad/trop.yr) Notes: 1) In contrast to the eraFk524 function, here the FK5 proper motions, the parallax and the radial velocity are presumed zero. 2) This function converts a star position from the IAU 1976 FK5 (Fricke) system to the former FK4 (Bessel-Newcomb) system, for cases such as distant radio sources where it is presumed there is zero parallax and no proper motion. Because of the E-terms of aberration, such objects have (in general) non-zero proper motion in FK4, and the present function returns those fictitious proper motions. 3) Conversion from J2000.0 FK5 to B1950.0 FK4 only is provided for. Conversions involving other equinoxes would require additional treatment for precession. 4) The position returned by this function is in the B1950.0 FK4 reference system but at Besselian epoch bepoch. For comparison with catalogs the bepoch argument will frequently be 1950.0. (In this context the distinction between Besselian and Julian epoch is insignificant.) 5) The RA component of the returned (fictitious) proper motion is dRA/dt rather than cos(Dec)*dRA/dt. Called: eraAnp normalize angle into range 0 to 2pi eraC2s p-vector to spherical eraFk524 FK4 to FK5 eraS2c spherical to p-vector This revision: 2023 March 5 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.