# 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
From: Frank Reed
Date: 2013 Apr 8, 19:59 -0700

"To be sure I didn't misunderstand this equation, I referred back to Frank's post 122845 http://fer3.com/arc/m2.aspx?i=122845 and re-examined his dip0 equation, where he states "R is the radius of the Earth and of course dip0=sqrt(2h/R)" and then "multiplying by 3438 to convert to minutes of arc ".

Brad, I just can't believe this. You actually re-read my earlier post, and you still didn't get it?? May I ask, have you come to your senses YET? WHAT did that equation represent? It was obviously in the middle of an explanation --not the end. You're getting yourself terribly confused by trying so hard to find fault with my previous explanations.

You wrote:
"To be sure I didn't misunderstand this equation, I referred back to Frank's post 122845 http://fer3.com/arc/m2.aspx?i=122845 and re-examined his dip0 equation, where he states "R is the radius of the Earth and of course dip0=sqrt(2h/R)" and then "multiplying by 3438 to convert to minutes of arc "."

Just FYI, the post you referred back to (122845) is NOT the one that includes that equation. Both do, however, include the factor 3438 (which is nothing more than 180*60/pi rounded to four significant digits --a convenient number that anyone working with small angles in navigation should learn).

"Instead of some snarky comments, I'll simply urge Frank to defend his post, and explain why ALL THE OTHER EQUATIONS MATCH THE NAUTICAL ALMANC FOR STANDARD ENVIRONMENTAL CONDITIONS EXCEPT FRANK'S APPROXIMATION. Dip for standard environmental conditions is simply NOT =3438sqrt(2h/R)"

Of course it isn't! Slow down, Brad... Just SLOW DOWN and figure out what these equations are actually about instead of hammering away with Excel and racing from one to the next. You're making a mess.

-FER

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