# NavList:

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

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Re: from a watcher
From: Robert Eno
Date: 2002 Oct 18, 10:49 +0100

```I agree with you 100% on this Dan. Knowing this formula and how to
manipulate and transform it, is of the utmost importance. In fact, I will
take it a step further by suggesting that everyone should, once in a
while, sit down and draw a spherical triangle with all of the points and
sides labeled and then derive the navigation formula from the basic
spherical trig formula. Furthermore, one should commit to memory, the
signs (plus or minus) of the trigonometric functions (sin, cos, tan) in

I do this every once in a while and my wife -- an engineer no less --
accuses me of being a geek! No respect anymore.

I am no mathematical whiz kid so I find it necessary to go through this
tedious, though necessary exercise just to keep sharp. I also have a neat
little book (about the same size as HO 211) with the basic trig and log
functions. Finally, by committing the basics to memory, I can use my
calculator guilt-free!

Cheers,

Robert

>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
>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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