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Subject: Re: from a watcher
From: Dan Allen (danallen46@XXX.XXX)
Date: Fri Oct 18 2002 - 00:25:27 EDT
On Thursday, October 17, 2002, at 08:11 PM, David Weilacher wrote:
> cos(c) = cos(a)*cos(b) + sin(a)*sin(b)*cos(ab)
> Isn't this the flatlanders side-angle-side trig formula.
No, it is the spherical law of cosines. It is the most fundamental
formula in celestial navigation. One can use it to determine
great circle distances and courses, do sight reduction, measure the
length of twilight, and many other useful things. The first chapter
of W. M. Smart's classic "Textbook on Spherical Astronomy" is all
about this formula and how it is derived and used. If you understand
this formula and how to use it, you can do much of sight reduction
in your sleep. It is not a difficult formula and it is worthy of
everyone's study.
Gee, that sounds rather pedantic, but it really is handy in any case.
Dan
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