Name

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      ZENPOS

Purpose

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

Calling Sequence

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      ZENPOS, Date, Ra, Dec

Input

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

Outputs

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

Procedure

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      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.

Prompts

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      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

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

Procedure Calls

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      CT2LST - Convert to Local Mean Sidereal Time

Modification History

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      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