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    Re: Time of meridian passage accuracy
    From: Douglas Denny
    Date: 2009 Sep 25, 23:51 -0700

    I do not believe I have missed the point. I believe you have.
    
    I am aware of the changing declination of the Sun - it is changing constantly, 
    hence a meridian passage curve such as the one I gave is actually skewed - in 
    theory.  The question is: to what extent?  Answer - very small as to be of no 
    practical concern to practical navigators.
    
    The change in declination per DAY, as you say is only 0.8 minutes of arc - 
    which applied as an altitude correction it is negligable in practical 
    navigation.
    
    The differences between actual (appareent) max Altitude and true Mer passage 
    of the Sun are so small as to be negligable if max altitude is calculated 
    near to the apparent Mer Passage... and if not so, why does the Nautical 
    Almanac persist in publishing the Sun's Mer Passage each day so navigators 
    can use Max altitude?
    
    There is a vast difference between practical navigation and theoretical astronomy.
    That is the point which you have academically and pedantically missed.
    
    Douglas Denny.
    Chichester. England.
    
    
    
    
    
    
    
    Douglas Denny has missed the point. The nearness of his observation point to
    Greenwich has nothing to do with it. The time correction, due to changing
    declination, as the same the whole world over, at the same latitude and
    time-of-year..
    
    His calculated time of Meridian Passage may well be correct. But he isn't
    observing Meridian Passage, when the Sun is due South. He is observing
    maximum altitude, the peak of the curve, which is subtly different.
    
    George.
    
    
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