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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2022 Aug 8, 19:19 -0700
In addition to my last post, I just took the time to check this Liechtenstein Lunar from a known position.
Let us assume N47°00.0' / E009°50.0' , with LD = 30°09.8' at UT = 03h40m16.1s
* For LD = 30°09.6', i.e. for a -0.2' difference in topocentric observed LD, then UT = 03h41m19.6s , which makes a difference in UT equal to +63,5s, i.e. a difference of +32,0 s for a difference of -0.1' in topocentric observed LD
** For LD = 30°10.6', i.e. for a +0.2' difference in topocentric observed LD, then UT = 03h39m12.0s , which makes a difference in UT equal to -64.1s, i.e. a difference of -32,0 s for a difference of +0.1' in topocentric observed LD
Hence clearly a +/- 0.1' topocentric change in LD translates into a -/+32,0 s change in the UT value derived under these assumptions, exactly as predicted here.
One last note : the Position GDOP obtained through this Lunar has a high value. In other words the distance between the Observer's extreme possible positions is not known to better than maybe 3° - a couple of hundred NM - or so, especially since the heights are not accurately known and the bodies azimuths are almost identical. It still puts us in Liechtenstein or vicinity. Nonetheless, even within such wide uncertain area, UT determinations seem to remain rather stable to less than one minute of UT.
Given the "fixed position method" I have assumed here, I trust that the "32.0s UT / 0.1' LD ratio" derived herabove could be improved if one were using the classical method instead.
It certainly would be worth to check all the above - i.e. differences in expected accuracies with known position vs. classical method - on a different example with much lower and better GDOP.
But the actual Bodies configuration with such high GDOP prevents me from adequately checking this assumption here.
For all these reasons, I feel it wise to keep considering that the "32.0s UT / 0.1' LD ratio" - and no significantly better - still remains reasonably applicable to this specific environment configuration current example.
Kermit
PS : Given the significant differences between various answers published so far, what are the actual numbers of the solution to this Liechtenstein Lunar ?