# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Two definitions of LHA
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....

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