% @(#)computst.hlq	19.1 (ESO-IPG) 02/25/03 14:03:04 
%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
%.COPYRIGHT  (c)  1992 European Southern Observatory
%.IDENT      computst.hlq
%.AUTHOR     DB, IPG/ESO
%.KEYWORDS   MIDAS, help files, COMPUTE/ST
%.PURPOSE    On-line help file for the command: COMPUTE/ST
%.VERSION    1.0  26-FEB-1987 : Creation, DB
%.VERSION    1.1  02-SEP-1992 : Change to eastern longitude, PJG
%----------------------------------------------------------------
\se
SECTION./ST
\es\co
COMPUTE/ST						02-SEP-1992  DB
\oc\su
COMPUTE/ST date UT [longitude]
COMPUTE/ST table.tbl [longitude]
COMPUTE/ST image [longitude]
	calculate geocentric Julian date (JD) and local mean sidereal time (ST)
	from civil date and universal time (UT)
\us\pu
Purpose:
          Calculate geocentric Julian date (JD) and local mean sidereal
          time (ST) from civil date and universal time (UT).
\up\sy
Syntax:       
          COMPUTE/ST date UT [longitude]
          COMPUTE/ST table.tbl [longitude]
          COMPUTE/ST image [longitude]
\ys\pa
          date = year,month,day of civil date at longitude zero (Greenwich)
                 NOT at the longitude of the observatory!
\ap\pa
          UT = hour,min,sec of universal time
\ap\pa
          longitude = degree,min,sec of eastern longitude of observatory,
\\
                 defaulted to -70,43,55.35
\\
                 (= Schmidt telescope, La Silla) must be negative !
\\
                 NOTE: Eastern longitudes are used conforming to IAU.
\ap\pa
          table = name of input table with the following column labels:
\\
                 :YEAR :MONTH :DAY     date
\\
                 :UTHR :UTMIN :UTSEC   universal time (UT)
\ap\pa
          image = name of image with the following descriptors set:
\\
                 O_TIME/D/1/3    year,month,day
\\
                 O_TIME(5)       universal time in real hours
\ap\sa
See also:
          COMPUTE/UT, COMPUTE/PRECESSION
\as\no
Note:         
          The parameters may also be referenced via:
\\
          DATE=  UT=  LONGITUDE= 
\\
          Dates and coordinates are of type REAL so that, e.g., the date can
          also be entered as 1982.787,0,0 or just 1982.787 . However,
          parameters must not be combined. That is, in the example given, the
          fraction of the year may contain only the number of elapsed full days
          not also UT.
\\
          The same applies to table input, however all input columns must be
          present even if they contain only zeros. The minus sign for negative
          values may occur in any field.
\\
          a) output keywords:
\\
          OUTPUTR/R/1/3  local mean sidereal time (hour,min,sec)
\\
          OUTPUTD/D/1/1  Julian date
\\
          b) for the table option the following table columns will be created
          or updated:
\\
          :STHR :STMIN :STSEC  -   local mean ST
\\
          :JD  -  Julian date
\\
          (Note that the table option is rather slow.)
\\
          c) the following descriptors will be created or updated:
\\
          O_TIME(4)       Julian date -2,400,000.5 in days
\\
          Eastern longitudes are positive and western counted negative
          conforming to IAU recommendations.
\\      
          If o_time(1) is the year 0 or 1900, a warning will be displayed. 
	  You should then write the correct value into the descriptor (do this
	  while the image is a .bdf file, because in .fits format o_time might 
	  not be changed correctly) and run compute/st again to obtain the
	  correct value. 
\on\exs
Examples:
\ex
          COMPUTE/ST  ccd0007
            Compute JD and ST for image `ccd0007.bdf' obtained at La Silla
\xe\ex
          COMPUTE/ST  obslist.tbl  0,0,0
            Compute JD and ST for objects in table `obslist.tbl', done in
            preparation for observations at the Royal Observatory in Greenwich.
\xe\ex
          COMPUTE/ST  1987,5,7  3,17,30
            Compute JD for 03:17:30 hrs UT on 7 May 1987 and the local mean
            sidereal time at La Silla
\xe \sxe
