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    Re: Time of meridian passage accuracy
    From: George Huxtable
    Date: 2009 Sep 25, 21:23 +0100

    Throughout his posting [9923], Douglas Denny appears to presume that
    Meridian Passage of the Sun occurs at the same moment as the maximum
    altitude of the Sun, at the peak of the curve of altitude with time.
    
    But it doesn't, except at the solstices, because of the Sun's changing
    declination. On the 29th April, the Sun's declination is increasing
    (Northward) by about 0.8 arc-minutes per hour. By a bit of rough guesswork,
    that's enough to delay the moment of peak altitude, to be somewhere between
    1 and 2 minutes later than Meridian Passage. Which will throw out his
    assessments by that amount.
    
    To set up a precise North-South line, it's a factor that must be allowed
    for. For star observations, there's no such problem, as the declination
    stays constant.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
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