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Re: Why are NA sight reduction tables not popular?
From: Alexandre Eremenko
Date: 2012 Apr 8, 20:23 -0400
From: Alexandre Eremenko
Date: 2012 Apr 8, 20:23 -0400
Gary, > The N.A. implementation of he law of cosines formula is: > S= sin Dec > C = cos Dec cos LHA > Hc = arc sin (S sin Lat + C cos Lat) > Hunh? > What's wrong with the way we all learned it: > sin Hc = (sin Lat sin Dec + cos Lat cos Dec cos LHA) If you look carefully, this is EXACTLY THE SAME. The reason they need S and C is that they are also used in their Asimuth formula, why to compute them twice? > cos A = (sin Dec cos Lat - cos Lat cos LHA)/cos Hc > instead the standard: > sin A = sec Hc cos Dec sin LHA sin A (and thus A) can be nagative, and seamen hate negative numbers. They prefer cos A. Then A is always positive and you only need to know E or W. For this they have a rule. The formula for sin A also needs a special rule: you need to know whether A is N or S, and then it can be negative:-) Alex.
