ASTRO

     Interactive utility for precession and coordinate conversion.

     ASTRO, [ selection, EQUINOX =, /FK4]

      SELECTION - Scalar Integer (0-6) giving the the particular astronomical
              utility to be used.  (0) Precession, (1) RA, Dec (2000) to Galactic
              coordinates, (2) Galactic to RA,Dec (2000) (3) RA,Dec (2000) to
              Ecliptic, (4) Ecliptic to RA, Dec, (5) Ecliptic to Galactic, (6) Galactic
              to Ecliptic.   Program will prompt for SELECTION if this
              parameter is omitted.

       EQUINOX - numeric scalar specifying the equinox to use when converting
               between celestial and other coordinates.    If not supplied,
               then the RA and Dec will be assumed to be in EQUINOX J2000.
               This keyword is ignored by the precession utility.   For
               example, to convert from RA and DEC (J1975) to Galactic
               coordinates:
               IDL> astro, 1, E=1975
       /FK4 - If this keyword is set and nonzero, then calculations are done
              in the FK4 system.    For example, to convert from RA and Dec
              (B1975) to Galactic coordinates
               IDL> astro,1, E=1975,/FK4

      ASTRO uses PRECESS to compute precession, and EULER to compute
      coordinate conversions.   The procedure GET_COORDS is used to
      read the coordinates, and ADSTRING to format the RA,Dec output.

      (1) ASTRO temporarily sets !QUIET to suppress compilation messages and
      keep a pretty screen display.
      (2) ASTRO was changed in December 1998 to use J2000 as the default
      equinox, **and may be incompatible with earlier calls.***
      (3) A nice online page for coordinate conversions is available at
       http://heasarc.gsfc.nasa.gov/cgi-bin/Tools/convcoord/convcoord.pl

      Procedures: GET_COORDS, EULER       Function: ADSTRING

      Written, W. Landsman November 1987
      Code cleaned up       W. Landsman   October 1991
      Added Equinox keyword, call to GET_COORDS, W. Landsman   April, 1992
      Allow floating point equinox input J. Parker/W. Landsman  July 1996
      Make FK5 the default, add FK4 keyword

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