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    Re: I need help with my first noon sun sight
    From: Jim Thompson
    Date: 2003 Dec 20, 17:39 -0400

    Ker-plunk!  Everything dropped into place after interpolating EqT, Trevor.
    Thanks.
    http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm
    
    Jim Thompson
    jim2{at}jimthompson.net
    www.jimthompson.net
    Outgoing mail scanned by Norton Antivirus
    -----------------------------------------
    
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Trevor J.
    > Kenchington
    >
    > Explaining the difference between your Methods 1 & 2 is easy. For Method
    > 2, you started from the time of meridian passage quoted in the almanac
    > to the nearest minute. You cannot expect calculations based on that to
    > be accurate to anything better than the nearest minute. Since both of
    > your calculations round to a time of 1308, they are in full agreement to
    > this level of accuracy. If you want the time of meridian passage to
    > the nearest second, you can't use your Method 2.
    >
    > I think that your problem with your method 8 is that you have read off
    > the Equation of Time for 1200 GMT on 14 September but you are applying
    > it to an observation after 1600 GMT that day. If you check the almanac,
    > you will see that the Equation of Time increased by 10 seconds in the 12
    > hours after 1200 GMT. Hence, in the four hours to your local noon, it
    > must have increased by 4 seconds (to the nearest second). Apply that
    > correction and your Method 8 will agree with your Method 1 to the
    > nearest second.
    >
    > You wrote:
    >
    > > Please see my calculations below for 3 ways to predict the
    > local zone time
    > > for meridian transit of the sun on September 14, 2003 at my
    > position of L
    > > 46o 11.1' N, Lo 63o 08.0' W (GPS Fix).  I cannot understand why
    > Methods 1, 2
    > > and 8 produce different predictions.  Can anyone spot the reason?
    > >
    > > I made a time diagram of this problem, though I am not sure that it is
    > > correct, and it gives yet a third answer:
    > >
    http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm#Time%20Diagram
    > (ignore the rest of what I have written on that page -- I am still
    muddling
    > through this).
    
    
    

       
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