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    On measuring the distance
    From: Bruce Stark
    Date: 2002 Mar 22, 14:17 EST

    Didn't get back to the computer as soon as expected!
    
    Far and away the most critical aspect of lunars is the observer's skill in
    measuring the distance. George has pointed out that a phenomena he's
    discovered and given the name "Parallactic retardation" makes the measurement
    twice as critical if the moon is near the meridian. That came as an
    unpleasant shock, but it reinforces the importance of developing good sextant
    technique.
    
    One thing I noticed about Chuck's measurements of the distance is that he got
    and recorded them in short order. That's the way it should be. Agonizing over
    the perfection of each contact only wears you out.
    
    Another thing I noticed is that, although the distance is increasing, his
    measurement of it gets shorter each time. And I believe it is getting better
    each time. My own experience is that it often takes one or two contacts to
    warm up. Perhaps for his next lunars he'll take only one altitude of each
    body before and after the distances and use the time saved to get more
    distance contacts. Maybe five or six, and throw the first one or two away.
    
    My own eyesight is poor, and when I bring the sextant up again the last
    contact still looks OK. So I always give the knob a little twist one way or
    the other so as to have to make a new adjustment. That way, five or six
    contacts usually gets GMT within two minutes.
    
    Bruce
    
    
    

       
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