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    Small zenith distance: a "bubble" sextant vs a Newtonian type sextant?
    From: Tony Oz
    Date: 2018 Feb 27, 06:13 -0800

    Hello.

    Will a sight of a star near zenith taken with a bubble type sextant be more reliable than a sight of a star at medium/lower altitude taken with a Newtonian type sextant (referenced to the natural horizon)?

    I think it should be the case because of the:

    • more precise sextant positioning in vertical plane
    • less or negligible refraction correction required

    Been to Finnish Gulf this weekend, compared the height of a distant island/fort - in the quiet air and sunny conditions the refraction was very diffrerent to our usual conditions - I could measure the refraction to alter the height of the island as much as by 4' (four arc-minutes) in unfavourable weather. This time the fort at ~5km was in full view and the next one - in ~10km was clearly visible too.

    Please comment.

    Regards,

    Tony

       
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