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    Re: Loss of accuracy using Sun over Sun with a mercury artificial horizon?
    From: Geoffrey Kolbe
    Date: 2016 Jul 19, 07:00 +0100


    On 18 July 2016 at 12:53, Sean C <NoReply_SeanC@fer3.com> wrote:

     Personally, I seem to have experienced an increase in accuracy by overlapping the two images. 


    ​This has been my experience too - but this should be qualified by saying that it has been my experience using very low magnification (Galilean telescope) or zero​ magnification (pocket "box" sextant). 

    Using a theodolite to determine azimuth, the sun simply rushes across the field of view towards the cross-hairs in the 30x scope and it is possible to determine the moment when the sun is tangential to the vertical cross-hair to better than a second. Similarly, I observe that with a 28x scope which I made for my Husun sextant the direct image and the derived image from the AH rush towards each other, so using the touching-limbs method seems to work best.

    Geoffrey Kolbe

       
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