# NavList:

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

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Re: Refraction
From: Robert Eno
Date: 2005 Sep 3, 09:32 -0400
If I had a scanner, I could scan the table for you.  Here are a few examples:

Height of observer: 0 feet
Sextant Altitude:  minus 1 degree
Correction: minus 35 minutes

Observed Altitude = minus 1 degree 35 minutes

Height of Observer: 55,000 feet
Sextant Altitude: minus 3 degrees 50 minutes
Correction:   minus 60 minutes

Observed Altitude: minus 4 degrees 50 minutes.

There is an additional component for temperature correction as well, but I have excluded this from the examples for the sake of keeping things simple. The tables do not extend below sextant altitudes of minus 3 degrees 53 minutes for altidudes (height of observer) of 55,000 feet. For observers at sea level, the lowest entry argument is minus 0 degrees 18 minutes.

Keep in mind the tables are intended for air navigators. As I said before, I am not aware of any tables intended for surface navigators that provide corrections for negative altitudes. Again, negative altitudes should not be expected anywhere else but in aircraft and polar regions. In the case of the latter, it is not uncommon to see the sun return when technically, it is well below the horizon. The extreme cold in the Arctic induces some pretty extreme refraction conditions.

I suppose the only other way would be to calculate the correction mathematically but I do not know what formula one would use. From what I understand, considering the variablility of conditions, refraction correction tables are part science and part black magic .

Perhaps some of our more learned and experienced members can expand on this. George, Joel, Ken, Fred are you listening???

Robert
----- Original Message -----
Sent: Thursday, August 04, 2005 8:40 AM
Subject: Re: Refraction

Hello Robert

Thank you for your fast reply. Unfortunately I am not in possession of the Air Almanac; in addition I am for about an other year abroad in a country where I am not able to order copies from a library. May I therefore ask you, whether it would be possible for you to derive from the table you indicated one or the other benchmark value? As you mentioned this would at least give a clue. Thanks a lot!

Like you I am still hoping that there is some one out there who really can provide a solution to this problem.

Marcel

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