A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Hav-Doniol Lat/Dec subtractions
From: Greg Rudzinski
Date: 2016 Oct 19, 09:11 -0700
Just subtract the smaller from the larger so that L+/- d is always positive. The formula works at all latitudes and declinations through 180° of meridian angle.
From: Michael Bradley
Date: 2016 Oct 17, 15:48 -0700
Hi Stan K
Re your 2015 postings discussing the subtractions of Dec and Lat.
I came upon another possible minor tweak to the Hav Doniol formulas tonight, reducing a sight of gamma Cassiopiea ( Declination roughly 61 North ) from the local beach (at Latitude roughly 55 North). Lat-Dec comes out negative.
IMHO the subtractions would be better expressed as differences, e.g. Dec ~ Lat or Lat ~ Dec. All those worked examples of sun sights undertaken from north of the sun in the northern hemisphere in summer are obviously not a complete set of possible position finding problems. A first time user coming across a negative answer to one of the 'normal' subtractions would not know what to do, unless he or she knew that hav(A-B) = hav(B-A), or expressed as in the Doniol formulas Hav(-n) = Hav(n) and Hav(-p) = Hav(p). The difference form of the formulas might give an additional clue about what to do.... or might not.
How did the use of Doniol in class go? I don't recall any reports, but I do go off message for great lumps of time.
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