A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Mark Coady
Date: 2017 Jun 2, 10:01 -0700
We engineers love our definitions...tend to consider them a life jacket......
I can't help but notice that LHA seems to have two definitions stated in common use. Due to the lovely flowing curves of trigonometry, it all seems to work.....but...for the persnickity types....
A brief search of multiple internet sources last night gave me enough of a statistical split to leave the question open to argument.
The two ways I see LHA defined: #1 LHA = GHA - Long (simply stated as the "difference in angle", implies to me you would often simply figure by inspection and use the shorter "included angle") #2 LHA = GHA +/- Long (+E, -W) (Always measured westward from observer to celestial object)
if I go #1 GHA = 200, Long = 60E def#1 by inspection I could conclude LHA as the included angle between them: LHA =100 degrees
if I go #2 GHA = 200, Long = 60E def #2 gives me a strict def as LHA = 260 degrees circling around from the west.
The cosine value is the same....so...ok....happy enough. (sin & tan are reversed +/-)
Which is the most correct statement: is it the "difference" only , or "difference measured west". EG as in above the acute angle (nearest) or obtuse angle measured west the "explementary or conjugate" angle.
Perhaps I am being obtuse more than the angle here....