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    Re: The Noon Fix
    From: Gary LaPook
    Date: 2009 Apr 11, 12:54 -0700

    Why not just cheat?
    
    For the short period between the two observations simply change your
    course to straight east of west, that eliminates the problem of vessel
    movement. Even better, adjust the course slightly north or south of
    east or west to create a vector north or south movement to compensate
    for the change in declination of the sun. The maximum speed that the
    sun moves in declination is one knot around the time of the equinoxes.
    On a six knot sail boat simply sail 080� or 280� around March 20th to
    have a movement of one knot north to compensate for the sun's one knot
    northward movement. Smaller corrections are needed at other times of
    the year.
    
    That said, I don't see any advantage over the traditional method of
    advancing the morning sun line to cross the afternoon sun line. In
    effect, you method retards the afternoon running fix back to the time
    of meridian passage which you will then have to advance to the current
    time.
    
    
    gl
    On Apr 8, 8:19�pm, James N Wilson  wrote:
    > George:
    >
    > I have wrestled with this problem, and only reluctantly called the
    > position determination by the method a fix. Longitude is determined at
    > noon, but it is based on data taken before and after noon. It is not a
    > running fix, since no lines of position are advanced or retarded. Or even
    > determined. I do discuss a bit the error sensitivity, but not as
    > completely is in the reference, my 1985 Navigation paper.
    >
    > I originally calculated Dhs at two different times bracketing LAN, thus
    > allowing for the different slope of the adjusted hs vs WT line. I
    > abandoned that in the interest of simplicity. For the example I used,
    > that made LAN eight seconds earlier. I considered that was not worth the
    > extra effort, considering other errors.
    >
    > I didn't explore much at the extremes of Latitude and, as you have
    > pointed out, there are some where the Sun is never visible. So, the
    > method does have its limitations.
    >
    > Thanks for your proper critique. As for the details of the arguments,
    > there's not much more in the two and a half page book. It was not
    > intended to be a treatise, but a description of a backup method. The
    > resultant surprise benefits were thoroughly examined to be sure that they
    > were true, but that's the extent of the effort.
    >
    > Jim Wilson
    > ____________________________________________________________
     
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