NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The Noon Fix
From: James N Wilson
Date: 2009 Apr 8, 11:19 -0700
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From: James N Wilson
Date: 2009 Apr 8, 11:19 -0700
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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