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    Re: A noon sight conundrum
    From: Paul Hirose
    Date: 2003 Dec 1, 15:02 -0800

    Kieran Kelly wrote:
    >
    > 3) In your learned opinion what was the time of meridian passage on that day
    > at long 132d 40' E.
    
    I'll use MICA 1.52 again, but this time working the problem with local
    hour angle rather than azimuth as I did earlier.
    
    MICA doesn't seem to have a way to display local hour angles, so I
    have to get tabulations of sidereal time and the Sun's right
    ascension, then subtract one from the other.
    
    
                                    SIDEREAL TIME
                     Location:  E132?40'00", S21?48'18",     0m
                     (Longitude referred to Greenwich meridian)
    
                               Local App.
       Date        Time      Sidereal Time
            (UT1)
                 h  m   s    h  m   s
    2002 Jul 20 03:15:38.0   7 57 14.4944
    2002 Jul 20 03:15:39.0   7 57 15.4972
    2002 Jul 20 03:15:40.0   7 57 16.4999
    
    
                                      Sun
                            Apparent Topocentric Positions
                           True Equator and Equinox of Date
                     Location:  E132?40'00", S21?48'18",     0m
                     (Longitude referred to Greenwich meridian)
    
       Date        Time      Right Ascension
            (UT1)
                 h  m   s       h  m   s
    2002 Jul 20 03:15:38.0      7 57 15.607
    2002 Jul 20 03:15:39.0      7 57 15.610
    2002 Jul 20 03:15:40.0      7 57 15.613
    
    
    The differences:
    
      UT1        LAST-RA
    03:15:38   23:59:58.9
    03:15:39   23:59:59.9
    03:15:40   00:00:00.9
    
    Meridian passage occurs .1 s after the middle time, i.e., at
    03:15:39.1 UT1.
    
    On that date UT1 was .23 s behind UTC, so the UTC time was
    03:15:39.3.
    
    As I said before, on this date MICA overestimates the TT-UT1
    difference by 3.6 seconds. So the Sun's UT1 position against the fixed
    stars is computed for a time 3.6 seconds later than the correct time.
    In 3.6 s its right ascension increases .01 s, so strictly speaking all
    the RA's I tabulated above should be decreased by .01 s to put them on
    the UT1 time scale. That's too small to worry about.
    
    
    

       
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