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    Latitude and longitude from a single twilight polarum reading of Alkaid and sextant Alt of Polaris
    From: Francis Upchurch
    Date: 2016 Sep 17, 23:44 -0700

    We all give a knowing smile when we see the historical film of the captain boldly proclaiming a lat/long fix from a single noon sextant sight. I haven't done that, but close.

    A single polarum (nocturnal that just measures angles) shot of Alkaid angle, with "simultaneous sextant alt of Polaris quickly gave me reasonable lat and long.

    Latitude. 

    Ha Polaris 50°42' by sextant

    Polarum Alkaid angle gives Q correction -36'. Latitude 50°06 .Spot on.

    Longitude.

           GHA Aries 78°43'

    +SHA Alkaid    153°  =GHA Alkaid 231°43' (this would be the polarum angle reading at Greenwich)

    Minus LHA alkaid from local Cornwall polarum angle reading 226° = Longitude 05° 43' 

    Correct long by GPS 5°32', so just 11' out with basic small polarum (I' still working on another "improved version" (more later)

    I had only used Kochab before for longitude, but this one shot of Alkaid worked well for both q correction and longitude.

    I  hope to experiment with my improved polarum soon. this hopefully will give readings to about 6'.

    Best wishes

    Francis

       
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