# NavList:

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

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Re: Table 8, Bowditch
From: Lu Abel
Date: 2009 Jan 13, 00:03 -0800

```Ark Shvetsky wrote:
> Thank you, Frank!
>
>
> Just wants to make it clear for myself :>: to calculate a distance to the
visible horizon I need to use statute miles, not nautical.  Is this a correct
statement?
>
No -- the Bowditch formulas are for distance to horizon in nautical
miles.

As an aside, as Frank pointed out the distance-to-the-horizon figure can
vary depending on the amount of refraction, which in turn depends on
atmospheric conditions.  Because it's not a three-digit-accuracy
calculation, I prefer to use 8/7 as the multiplier rather than 1.15 (or
1.17 or other numbers given in Bowditch or other publications over the
years).   It's a lot easier to remember and a lot easier to use in
mental calculations (and even arguably fewer keystrokes on a calculator).
> Also, just curious: radio waves and light wave are electromagnetic waves
which are differ in frequency.  Therefore, it means the refraction-wise high
frequency signal is refracted more.  Is it logarithmic or just a linear
correlation for refraction rate between low and high frequency waves?
The lower the frequency, the greater the refraction.  But there are many
factors that contribute to refraction -- for light, it's primarily the
density of the atmosphere.  But for lower frequency electromagnetic
radiation, its primarily the conductivity of the surface of the earth.
So to the best of my knowledge, there's no simple linear-vs-logarithmic

Lu Abel

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