% @(#)computpara.hlq	17.1.1.1 (ESO-IPG) 01/25/02 17:55:39
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%.COPYRIGHT  (c)  1993 European Southern Observatory
%.IDENT      computpara.hlq
%.AUTHOR     PB, IPG/ESO
%.KEYWORDS   MIDAS, help files, 
%.PURPOSE    On-line help file for the command: COMPUTE/PARAL
%.VERSION    1.0  22-MAR-95 : Creation, PB
%----------------------------------------------------------------
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SECTION./PARAL
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COMPUTE/PARAL					      22-MAR-95  AS
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COMPUTE/PARAL   ra  dec  st  wave  refw 
	 Computes parallactic angle and atmospheric differential refraction
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Purpose:    
            Computes the parallactic angle and the atmospheric 
            differential refraction. cf. Filippenko, A.V.: 1982, 
            PASP, 94, 715. The command provides: \\
 \\
            a) altitude in degrees ( 0 at horizon, 90 at zenith) \\
 \\
            b) azimuth in degrees (south=0,west=90,north=180,east=270)
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            c) parallactic angle in degrees (-180 to 180)
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            d)  differential refraction angle in arcseconds (negative values
             mean that the working wavelength image is at an altitude
             larger than reference wavelength image)
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Syntax:     
            COMPUTE/PARAL  ra  dec  st  wave  refw 
 \\
\ys\pa
            ra     = Right Ascension in format hour,min,seconds \\ 
                     (seconds can be fractionary) 
\\
\ap\pa
            dec    = Declination in format  degree,min,seconds \\
                     (seconds can be fractionary) 
 \\
\ap\pa    
            st     = Sidereal time in format  degree,min,seconds \\
                     (seconds can be fractionary) 
 \\
\ap\pa    
            wave   = working wavelength in Angstroms (default: 5000)
 \\
\ap\pa    
            refw   = reference wavelength  in Angstroms (default: 5000)
 \\
\ap\sa
See also: 
            REFRACTION/LONG
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Note:       
            1) RA and Dec should be apparent coordinates.
 \\
            2) The procedure assumes standard conditions for the 
               refraction angle calculation: Alt = 2km; phi = +/- 30deg; 
               P = 600 mm Hg; T = 7deg C; f = 8 mm Hg. \\
               (not much dependence on f or T)
 \\
            3) The procedure assumes the latitude of La Silla observatory
               (Schmidt telescope: -29deg15'25.8")
 \\
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Examples:
\ex
            COMPUTE/PARAL 11,04,0 -18,05,0 11,0,0 3500. 6000. \\
            Will give the following results:\\
            Altitude                      : 78.62 degrees  \\ 
            Azimuth                       : 184.83 degrees \\
            Parallactic Angle             : -175.57 degrees \\
            Differential Refraction Angle : -0.31 arcseconds  \\
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