A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Francis Upchurch
Date: 2017 Jan 8, 11:29 -0800
Attatched my clearance workings for your first sight 1 lunar.
I have sorted some of my earlier problems:
1)The artificial horizon (AH) means , No dip, No SD (for altitudes), the Alt measurement has to be divided by 2 to get the proper h value for the clearance formulae. (Question for Frank, does the lunar clearance website calculator deal with artifical horizon scenarios?)
2) The AH also means that the moon main correction method is different and according to the NA, you use the instructions for the Bubble sextant for the second main correction for altitude.
I have found a mysterious difference in results comparing the conventional cosine formula (Karl page 92) and the abbreviated Thompson .
Usually the cosine full method is more accurate, but in this case, the Thompson gives a much better result in terms of LDo and resulting GMT. Not entirely sure why, perhaps Frank would know?
The Thompson method does not require Ho or ho inputs and therefore is not affected by the moon main correction/AH issues.
This is the first time I have found this and it may be I have made some fundamental mistake with adapting the AH readings to the cosine method.( I have no previous experience with AH readings).
However, I think for a first ever lunar, your result is not bad! I will look at some of the others soon.Some look even better.
Normally ,I would try to average out your 3 sights by graphing, choosing best fit curve and choosing a single time for the LDs, Hs and hs. However, this works best if you can do the 3 the sights within say about 5 minutes.
Best wishes and happy lunars to all.