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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction
From: Robert Eno
Date: 2005 Sep 3, 09:32 -0400
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 -----From: Marcel E. TschudinSent: Thursday, August 04, 2005 8:40 AMSubject: Re: RefractionHello 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
