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    Re: 1851 Bowditch
    From: Bruce Stark
    Date: 2003 Feb 3, 13:02 EST

    Good to hear from you, Robert!
    
    All's well here, except I had the upper left lobe of my lung removed in
    December, which has slowed me down quite a bit. Nothing to worry about, as
    they got it early and it wasn't the spreading kind, but It's slow work
    getting back up to speed. I'm pretty far behind on everything. But the
    surgeon says that if I work at it, Janice and I can be hiking and camping by
    next summer.
    
    You said you weren't in on last years discussion and would like a Reader's
    Digest style condensation. I'd rather not try that. The discussion itself
    would be in the List's Archive. But I will flounder around a bit to see if I
    can explain why accurate GMT needn't be critical in working observations.
    
    Granted, you have to have accurate Greenwich time to check your longitude. So
    did Bowditch. He found it by lunar, checked his longitude with it and, since
    he didn't have a chronometer to keep track of it, forgot it. He based his
    calculations on local apparent time, regulating his watch by time sight. For
    a reasonable number of hours his watch could keep track of the sweep of the
    celestial sphere over his meridian. That 15� per hour westward sweep is the
    only reason time is critical. Within the sphere itself the celestial bodies
    move around slowly. An approximate Greenwich time will locate a body within
    the sphere close enough for practical navigation.
    
    To get that approximate Greenwich time to locate a body with the sphere,
    Bowditch "reduced" local time to Greenwich by applying his DR longitude,
    converted to hours and minutes.
    
    Here are the Archive addresses of three postings which sum it up to the best
    of my ability:
    
    http://www.i-DEADLINK-com/lists/navigation/0210/0172.html
    http://www.i-DEADLINK-com/lists/navigation/0210/0187.html
    http://www.i-DEADLINK-com/lists/navigation/0210/0213.html
    
    Keep in touch.
    
    Bruce
    
    
    

       
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