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      Return the zenith RA and Dec in radians for a given Julian date.

Calling Sequence

      ZENPOS, Date, Ra, Dec


      Date The Julian date, in double precision, of the date and time
              for which the zenith position is desired, scalar or vector.


      Ra The right ascension in RADIANS of the zenith.
      Dec The declination in RADIANS of the zenith.


      The local sidereal time is computed; this is the RA of the zenith.
      It and the observatories latitude (corresponding to the Dec.) are
      converted to radians and returned as the zenith direction.


      ZENPOS will prompt for the following 3 parameters if they are not
      defined in the common block SITE (see below)
      LAT,LNG - north latitude and east longitude of the desired location
              in DEGREES
      TZONE - Time Zone (in hours) of the desired location (e.g. 4 = EDT,
              5 = EST)

Common Blocks

      SITE - This common block should contain the three scalars LAT, LNG
              and TZONE

Procedure Calls

      CT2LST - Convert to Local Mean Sidereal Time

Modification History

      Written by Michael R. Greason, STX, 14 October 1988.
      Converted to IDL V5.0 W. Landsman September 1997
      Update documentation, longitude now *east* of Greenwich W.L. July 2000

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