erfa.hfk5z(rh, dh, date1, date2)[source]

Transform a Hipparcos star position into FK5 J2000.0, assuming zero Hipparcos proper motion.

rhdouble array
dhdouble array
date1double array
date2double array
r5double array
d5double array
dr5double array
dd5double array


Wraps ERFA function eraHfk5z. The ERFA documentation is:

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 e r a H f k 5 z
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Transform a Hipparcos star position into FK5 J2000.0, assuming
zero Hipparcos proper motion.

   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)


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

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.

   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


   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.