CT2LST

     To convert from Local Civil Time to Local Mean Sidereal Time.

     CT2LST, Lst, Lng, Tz, Time, [Day, Mon, Year]
                       or
     CT2LST, Lst, Lng, dummy, JD

     Lng  - The longitude in degrees (east of Greenwich) of the place for
            which the local sidereal time is desired, scalar.   The Greenwich
            mean sidereal time (GMST) can be found by setting Lng = 0.
     Tz  - The time zone of the site in hours.  Use this to easily account
            for Daylight Savings time (e.g. 4=EDT, 5 = EST/CDT), scalar
            This parameter is not needed (and ignored) if Julian date is
            supplied.
     Time or JD  - If more than four parameters are specified, then this is
               the time of day of the specified date in decimal hours.  If
               exactly four parameters are specified, then this is the
               Julian date of time in question, scalar or vector

      Day -  The day of the month (1-31),integer scalar or vector
      Mon -  The month, in numerical format (1-12), integer scalar or
      Year - The year (e.g. 1987)

       Lst   The Local Sidereal Time for the date/time specified in hours.

       If specified, the date should be in numerical form.  The year should
       appear as yyyy.

       The Julian date of the day and time is question is used to determine
       the number of days to have passed since 0 Jan 2000.  This is used
       in conjunction with the GST of that date to extrapolate to the current
       GST; this is then used to get the LST.    See Astronomical Algorithms
       by Jean Meeus, p. 84 (Eq. 11-4) for the constants used.

       Find the Greenwich mean sidereal time (GMST) on 1987 April 10, 19h21m UT
       For GMST, we set lng=0, and for UT we set Tz = 0
       IDL> CT2LST, lst, 0, 0,ten(19,21), 10, 4, 1987
               ==> lst =  8.5825249 hours  (= 8h 34m 57.0896s)
       The Web site  http://tycho.usno.navy.mil/sidereal.html contains more
       info on sidereal time, as well as an interactive calculator.

       jdcnv - Convert from year, month, day, hour to julian date

     Adapted from the FORTRAN program GETSD by Michael R. Greason, STX,
               27 October 1988.
     Use IAU 1984 constants Wayne Landsman, HSTX, April 1995, results
               differ by about 0.1 seconds
     Converted to IDL V5.0   W. Landsman   September 1997
     Longitudes measured *east* of Greenwich   W. Landsman    December 1998

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