% @(#)computut.hlq	17.1.1.1 (ESO-IPG) 01/25/02 17:43:22 
%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
%.COPYRIGHT  (c)  1992 European Southern Observatory
%.IDENT      computut.hlq
%.AUTHOR     DB, IPG/ESO
%.KEYWORDS   MIDAS, help files, COMPUTE/UT
%.PURPOSE    On-line help file for the command: COMPUTE/UT
%.VERSION    1.0  26-FEB-1987 : Creation, DB
%.VERSION    1.1  02-SEP-1992 : Change to eastern longitude, PJG
%----------------------------------------------------------------
\se
SECTION./UT
\es\co
COMPUTE/UT						02-SEP-1992  DB
\oc\su
COMPUTE/UT date ST [longitude]
COMPUTE/UT table.tbl [longitude]
COMPUTE/UT image [longitude]
	calculate geocentric Julian date (JD) and universal time (UT) from 
	civil date and local mean sidereal time (ST)
\us\pu
Purpose: 
          Calculate geocentric Julian date (JD) and universal time (UT) from
          civil date and local mean sidereal time (ST)
\up\sy
Syntax:       
          COMPUTE/UT date ST [longitude]
          COMPUTE/UT table.tbl [longitude]
          COMPUTE/UT image [longitude]
\ys\pa
          date = year,month,day of civil date
\ap\pa
          ST = hour,min,sec of sidereal 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
\\
                :STHR :STMIN :STSEC   sidereal time (ST)
\ap\pa
          image = name of image which must have the following descriptors
\\
                O_TIME/D/1/3    year,month,day
\\
                O_TIME(6)       local mean ST in real hours
\ap\sa
See also:
          COMPUTE/ST, COMPUTE/PRECESSION
\as\no
Note:         
          The parameters may also be referenced via:
\\
          DATE=  ST=  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 keyword:
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          OUTPUTR/R/1/3  universal time (hour,min,sec)
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          OUTPUTD/D/1/1  Julian date
\\
          b) for the table option the following table columns will be created
          or updated:
\\
          :UTHR :UTMIN :UTSEC  -  UT
\\
          :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
\\
          O_TIME(5)       universal time in real hours
\\
          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/ut again to obtain the
	  correct value. 
\on\exs
Examples:
\ex
          COMPUTE/UT  ccd0007
            Compute JD and UT for image `ccd0007.bdf' obtained at La Silla.
\xe\ex
          COMPUTE/UT  obslist.tbl  0,0,0
            Compute JD and UT for objects in table `obslist.tbl' done in
            preparation for observations at the Royal Observatory in
            Greenwich.
\xe\ex
          COMPUTE/UT  1987,5,7  15,17,30
            Compute JD and UT for 15:17:30 hrs La Silla mean ST on 7 May 1987.
\xe \sxe