# NavList:

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

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Re: Refraction near the Horizon ? Observation vs. Calculation
Date: 2013 Apr 11, 17:46 -0700

Hi Frank

In your posts, you explained that geometric dip, in minutes, can be derived from 3438sqrt(2h/R) into the form dip, minutes=1.06sqrt(h).

You then stated that geometric dip did not match the Nautical Almanac's version of refracted dip,minutes=.97sqrt(h,feet), giving a nice history lesson in marketing Navigation Tomes. I actually though that was neat.

I responded that the geometric form of 3438sqrt(2h/R) could be made the refracted form by dividing R by (1-k), k=.164. That this unified all the equations. Made them all produce the same result.

Here's the funny part. If I multiply 1.06 (the geometric dip constant) by the square root of (1-.164), I get 0.96919 or if you want just two decimal places .97 (the refracted dip constant). Hmmm, now why would that be?

So it seems that we are actually in mathematical agreement, although the starting point was begun in my confusion. The equations have clearly been resolved to my satisfaction.

Thanks for hanging in there!

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