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    Re: Sumner's Line (Navigation question)
    From: George Huxtable
    Date: 2006 Feb 17, 09:30 -0000

    In the mailing I sent last night on this topic I made a careless mistake when I wrote, at the end,
    about working a time-sight-
    
    |
    | To work the problem by a calculator, rather than with logs, it's easier to use another expression
    | from Bowditch para 2106,
    |
    | cos (HA) = (sin lat - sin lat sin dec) / cos lat cos dec,
    |
    | and then convert angle to hours by dividing by 15.
    |
    | Again, lat and dec should be North-positive.
    
    =============
    
    That expression should have read-
    
    | cos (HA) = (sin alt - sin lat sin dec) / cos lat cos dec.
    
    It makes a big difference.
    
    Sorry about that.
    
    George.
    
    
    

       
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