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    Re: Master & Commander
    From: George Huxtable
    Date: 2003 Dec 8, 00:33 +0000

    Bruce Stark quotes the following statement from a friend-
    
    "By this time the Navigator is observing the track of the sun.  At his
    signal, the OOD instructs the Bo's'n's Mate of the Watch to strike 8 bells.
    Thus an exact noon is noted by the ringing of the ship's bell and it is
    dead accurate with a well trained bridge watch.  Sometimes this takes a bit
    of doing, but rather quickly they all get on to it and we can all set our
    wrist watches accurately."
    
    I would like to take issue with the "exact" and "accurately" aspects of
    this statement. Time may be determined that way accurately enough for
    change-of-watch, but NOT for navigational purposes. No matter how
    well-trained a bridge watch is, there's no way to determine the
    moment-of-noon, to within several minutes, by observing at or near noon,
    for (at least) two reasons.
    
    1. The Sun is rising so slowly, near noon, then remaining stationary with
    imperceptible motion, then falling so slowly, that it just isn't humanly
    possible to determine the moment-of-noon with any accuracy. Only by
    determining an altitude before noon, then the same after noon, and
    splitting the time-difference, can any accuracy be obtained.
    
    2. Even then, that's only the moment of maximum altitude, not the moment of
    local apparent noon, which occurs at the time of meridian passage. Between
    the two, even on a sailing vessel, there can be a discrepancy of 5 minutes
    or so, depending on the Northerly or Southerly component of the speed of
    the vessel.
    
    Sorry to reiterate what's been said several times before on this list, by
    me and by others.
    
    In other respects, the message was of great interest, and I hope Bruce can
    persuade its author to join our list.
    
    George.
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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