NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: sextant index error measurement
From: Frank Reed CT
Date: 2006 Nov 3, 23:03 EST
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From: Frank Reed CT
Date: 2006 Nov 3, 23:03 EST
Jim Martin, you wrote:
"According to "Nicholls concise guide" vol.1, a close by object
or straight line should not be used to determine index error,because it
does not allow for sextant parallax and atmospheric refraction. I can
give the textbook explanation if it is of interest."
or straight line should not be used to determine index error,because it
does not allow for sextant parallax and atmospheric refraction. I can
give the textbook explanation if it is of interest."
Sextant parallax, yes. That's an important issue for index
correction. But refraction, no. The only time terrestrial refraction would
make a difference is if you're comparing sight lines to two objects at distances
differing by a good fraction of a mile. I can't think of any instance where this
would matter for standard index correction observations.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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