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    Re: navigation problem
    From: George Huxtable
    Date: 2006 Feb 23, 00:39 -0000

    Dick Winchurch quoted from a sea-story set in the 1700s, author unnamed.
    
    ...a small boat became
    | separated from the mother ship in a fog.  They in the boat had taken bearing
    | fore and aft  on the way out but had lost the compass in scuffle with the
    | French.  In the fog they had no idea of the direction back to the ship.  The
    | moon was barely visible above the fog.  They computed the way back
    |
    | For any meridian the moon will cross just 49 minutes after the sun crosses
    | and the moon falls back 49 minutes every day.
    | By counting the days after new moon, multiplying that number by 49 and
    | dividing by 60
    | One arrives at the time in hours and minutes when the moon is due south.
    | With south noted and knowing the reciprocal bearing back the ship they could
    | safely return.
    ========
    
    If it was C S Forester, I respect his sea-knowledge. O'Brian, I don't.
    
    Would it work? Unlikely.
    
    "For any meridian the moon will cross just 49 minutes after the sun crosses
    | and the moon falls back 49 minutes every day."
    
    The lag, at new moon, varies from month to month, between about 0 and 45 minutes. That's the lag,
    behind the Sun, of the first crossing of the meridian by the Moon after the moment of new moon.
    Subsequently, the moon lags further behind the Sun each day, by an AVERAGE of 49 minutes, but the
    daily lag varies, just as the lag of the tides does, between 40 minutes and 60 minutes, at different
    times of the month. That will upset any attempt at such a calculation.
    
    But more seriously, how were they supposed to determine the time, in the night? Was one of them
    supposed to be carrying a pocket-watch? Unlikely, in the late 1700s.  Was one of them supposed to be
    turning an hour-glass regularly, in the heat of a fight? Equally unlikely.
    
    Without knowing more about it than we have been told so far, it seems to be one of those instances
    of an author seizing on a fact and building some story out of it.
    
    However, I don't wish to discourage Dick from providing something for us to pick at. We haven't
    discussed sea-fiction here for quite a while.
    
    George.
    
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    

       
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