# NavList:

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

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Re: An exotic lunar distance puzzle
From: Marcel Tschudin
Date: 2011 May 5, 20:32 +0300
Dave,

Atmospheric refraction exists also above 8 miles. If I remember right, the atmospheric models for calculating refraction generally use a height of about 80km. In your calculation you mixed km and mi. The radius of the earth is about 6400 km (not mi). You are right that the refracted ray has not a constant curvature as shown in the drawing, its bending increases as it passes through air layers closer to the surface.

Marcel

On Thu, May 5, 2011 at 7:09 PM, David Fleming wrote:

Marcel your pictures that geometric dip is not the same as a straight line from body to the horizon point. This is correct. Caused by refraction as you showed in curved red line. It is not as shown a smooth arc as I'm guessing you know but experiences the curve only as it enters the atmoshpere which I am not convinced happens a 8 miles height. Could somebody check that?

cos ( GeoDip) = 1 / ( 1 + (hE/RE)^2)

take RE = 6378 mi + 8 mi

he = 211 mi

GeoDip = 2.68 deg

Dave Fleming

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