hfk5z¶
- erfa.hfk5z(rh, dh, date1, date2)[source]¶
Transform a Hipparcos star position into FK5 J2000.0, assuming zero Hipparcos proper motion.
- Parameters:
- rhdouble array
- dhdouble array
- date1double array
- date2double array
- Returns:
- r5double array
- d5double array
- dr5double array
- dd5double array
Notes
Wraps ERFA function
eraHfk5z
. The ERFA documentation is:- - - - - - - - - e r a H f k 5 z - - - - - - - - - Transform a Hipparcos star position into FK5 J2000.0, assuming zero Hipparcos proper motion. Given: rh double Hipparcos RA (radians) dh double Hipparcos Dec (radians) date1,date2 double TDB date (Note 1) Returned (all FK5, equinox J2000.0, date date1+date2): r5 double RA (radians) d5 double Dec (radians) dr5 double RA proper motion (rad/year, Note 4) dd5 double Dec proper motion (rad/year, Note 4) Notes: 1) The TT date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=2450123.7 could be expressed in any of these ways, among others: date1 date2 2450123.7 0.0 (JD method) 2451545.0 -1421.3 (J2000 method) 2400000.5 50123.2 (MJD method) 2450123.5 0.2 (date & time method) The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date & time methods are both good compromises between resolution and convenience. 2) The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt. 3) The FK5 to Hipparcos transformation is modeled as a pure rotation and spin; zonal errors in the FK5 catalog are not taken into account. 4) It was the intention that Hipparcos should be a close approximation to an inertial frame, so that distant objects have zero proper motion; such objects have (in general) non-zero proper motion in FK5, and this function returns those fictitious proper motions. 5) The position returned by this function is in the FK5 J2000.0 reference system but at date date1+date2. 6) See also eraFk52h, eraH2fk5, eraFk5hz. Called: eraS2c spherical coordinates to unit vector eraFk5hip FK5 to Hipparcos rotation and spin eraRxp product of r-matrix and p-vector eraSxp multiply p-vector by scalar eraRxr product of two r-matrices eraTrxp product of transpose of r-matrix and p-vector eraPxp vector product of two p-vectors eraPv2s pv-vector to spherical eraAnp normalize angle into range 0 to 2pi Reference: F.Mignard & M.Froeschle, 2000, Astron.Astrophys. 354, 732-739. This revision: 2023 March 7 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.