HADEC2ALTAZ

      Converts Hour Angle and Declination to Horizon (alt-az) coordinates.

      Can deal with NCP/SCP singularity.    Intended mainly to be used by
      program EQ2HOR

      HADEC2ALTAZ, ha, dec, lat ,alt ,az [ /WS ]

     ha -  the local apparent hour angle, in DEGREES, scalar or vector
     dec -  the local apparent declination, in DEGREES, scalar or vector
     lat -  the local latitude, in DEGREES, scalar or vector

     alt - the local apparent altitude, in DEGREES.
     az  - the local apparent azimuth, in DEGREES, all results in double
           precision

      /WS - Set this keyword for the output azimuth to be measured West from
            South.    The default is to measure azimuth East from North.

     What were the apparent altitude and azimuth of the sun when it transited
     the local meridian at Pine Bluff Observatory (Lat=+43.07833 degrees) on
     April 21, 2002?   An object transits the local meridian at 0 hour angle.
     Assume this will happen at roughly 1 PM local time (18:00 UTC).
     IDL> jdcnv, 2002, 4, 21, 18., jd  ; get rough Julian date to determine
                                       ;Sun ra, dec.
     IDL> sunpos, jd, ra, dec
     IDL> hadec2altaz, 0., dec, 43.078333, alt, az
       ===> Altitude alt = 58.90
            Azimuth  az = 180.0

      Written  Chris O'Dell Univ. of Wisconsin-Madison May 2002

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