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    Interactive utility for precession and coordinate conversion.

Calling Sequence

    ASTRO, [ selection, EQUINOX =, /FK4]

Optional Input

      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.

Optional Keyword Input

      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
              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

Procedures Used

      Procedures: GET_COORDS, EULER Function: ADSTRING

Revision History

      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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