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    Re: Suitable Sextants
    From: Frank Reed CT
    Date: 2005 Oct 12, 19:58 EDT

    Joel Jacobs wrote:
    "Take a proper Star scope  and couple it with a small size horizon mirror,
    and note the results at  twilight."
    I think this comment gets to the heart of the matter. In older  sextants,
    telescopes rarely had large apertures. They went for small aperture  and long
    focal length. The horizon mirror only needs to be as big as the  aperture of the
    telescope. Navy sextants from the Second World War had small  horizon mirrors
    because their telescopes were usually small in aperture.  Naturally there is
    no reason to have a horizon mirror bigger than than the  telescope aperture.
    "Also take a sextant with small mirrors and  use what ever scope you are most
    comforatble with and try some high altitude sun  sights. Note the results."
    And that brings us to the index mirror. This  doesn't need to be any wider
    than the horizon mirror, but it helps a lot if it's  longer (bigger in the
    dimension along the index arm) because it will be  foreshortened when the sextant
    is set to a large angle. You can see this by  setting the sextant to 120
    degrees and then looking through the horizon glass at  the index mirror.
    42.0N 87.7W, or 41.4N  72.1W.

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