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    Re: Spherical Trig
    From: Bill Lionheart
    Date: 2024 Mar 16, 14:57 +0000
    Just to add the Wolfram Mathworld page page https://mathworld.wolfram.com/SphericalTrigonometry.html

    includes a derivation using dot and cross product, but readers may find it satisfying to derive the basic "cosine and sine rule" themselves. If you know dot and cross produvt from school.

    Also,  if you like this sort of thing,  you can use eg sin x is aporoximately x for x small etc, to check that over small distances we get back the Euclidean trig formulae.  Plane sailing!

    Bill Lionheart. 




    On Sat, 16 Mar 2024, 12:08 NavList Community, <NavList@fer3.com> wrote:
    Re: Spherical Trig
    From: Frank Reed
    Date: 2024 Mar 16, 04:56 -0700

    Chris L., you asked:
    "can you suggest a good book to self teach spherical trigonometry. I've taken plane trigonometry."

    I wouldn't recommend a book. Learning spherical trigonometry abstracted from its navigational context is not that useful. The only thing you need for almost everything is the spherical "law of cosines" (which also goes by other names). It's very little more than the great circle distance equation:
        cos(dist) = sin(Lat1)·sin(Lat2) + cos(Lat1)·cos(Lat2)·cos(dLon).
    You might imagine that it would be useful to know the derivation of this equation. I occasionally teach a derivation in classes when students insist, but I find there's almost no benefit. This equation "is what it is". You might be surprised how completely this one equation solves almost every problem that arises in celestial navigation!

    If you want more anyway, I can recommend the Wikipedia article on spherical trigonometry. It's extensive and detailed, and despite the reputation of some Wikipedia articles, this one is well-written and has no obvious flaws that I could find (with a cursory reading). It includes things like half-angle formulae and Napier's rules that have are important historically in navigation.

    Frank Reed


       
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