SLALIB_Version_2.4-0                                  Expiry 31 December 1999

The latest releases of SLALIB include the following changes:

*  Four new routines have been introduced which transform between the
   FK5 system and the ICRS (Hipparcos) system.  sla_FK52H and sla_H2FK5
   transform star positions and proper motions from FK5 coordinates to
   Hipparcos coordinates and vice versa.  sla_FK5HZ and sla_HFK5Z do the
   same but for the case where the Hipparcos proper motions are zero.

*  Six new routines have been introduced for dealing with orbital elements.
   Four of them (sla_EL2UE, sla_PV2UE, sla_UE2EL and sla_UE2PV) provide
   applications with direct access to the "universal variables" method
   that was already being used internally.  Compared with using conventional
   (angular) elements and solving Kepler's equation, the universal variables
   approach has a number of advantages, including better handling of near-
   parabolic orbits and greater efficiency.  The remaining two routines
   (sla_PERTEL and sla_PERTUE) generate updated elements by applying
   major-planet perturbations.  The new elements can then be used to
   predict positions that are much more accurate.  For minor planets,
   sub-arcsecond accuracy over a decade is achievable.

*  Several observatory sites have been added to the sla_OBS routine:  CFHT,
   Keck 2, Gemini North, FCRAO, IRTF and CSO.  The coordinates for all
   the Mauna Kea sites have been updated in accordance with recent aerial
   photography results made available by the Institute for Astronomy,
   University of Hawaii.

*  A bug in sla_DAT has been corrected.  It used to give incorrect
   results for dates in the first 54 days of 1972.

*  There are new routines for generating permutations (sla_PERMUT) and
   combinations (sla_COMBN).
 
 P.T.Wallace
 17 August 1999

 ptw@star.rl.ac.uk
 +44-1235-44-5372
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