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Marcel,

So there is no confusion. Using a table of corrections specifically for star to star distances - a refraction value is extracted to be always added to the sextant star to star reading which then becomes the true star too star distance as if observed from space.

The purpose of this star to star sextant measurement is to determine index error or to verify index error done in the usual manner. I like the star to star distance method because as the sextant is rocked slightly the star pair passes back and forth through each other. Any misalignment becomes more noticeable vs. a single star superimposed with the sextant set to zero.

Greg Rudzinski

[NavList] Re: Angular Distance Between Stars By Camera and Sextant
From: Marcel Tschudin
Date: 18 Sep 2012 23:04
Greg, regarding

On Tue, Sep 18, 2012 at 10:43 PM, Greg Rudzinski <gregrudzinski---com> wrote:
If you look at my original results:

Alioth Alkaid Hc 31*37*
10* 27.1' observed distance by sextant
+0.3' refraction correction by table
10* 27.4' true distance

10* 27.6' true calculated distance by William's on-line calculator
Low 0.2'

Your nomenclature may be misleading. "True" is in this context generally used for the positions without atmosphere. If I understand you correct, then your refraction correction relates to a correction for difference in refraction, because your sextant observations from each star already contain refraction. Your "true distance" corresponds then actually to observed distance because they include refraction. But, yes, indeed, the various results finally "converge" and we can now better evaluate them.

Marcel
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