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    Re: Accuracy of ephemeris
    From: Bill Lionheart
    Date: 2017 Oct 16, 21:02 +0100

    Good point. Just an idea: how about we video the view through the
    sextant with the index arm fixed as the body moves above the horizon,
    then calibrate the pixel to arc correspondence. Video rate is 25 Hz at
    least. Would that buy is some more accuracy at very little expense
    (video cameras are so cheap they fit them in phones after all).
    Not that we need that accuracy at sea on the time scale of a passage,
    just doing this for fun.
    On 16 October 2017 at 15:28, John D. Howard  wrote:
    >  Bill,
    > The "Gold Standard" is the data put out by the Jet Propulsion Lab.  They
    > have a public website called Horizions that you can access ( some of ) their
    > data.
    > The limit on cel nav ( IMHO ) is time.  We only record our time to the
    > second and the Nautical Almanac only shows data to the second but that is
    > .25 minutes of arc.  Untill we record the sight to the hunderth or even the
    > thousands of a second we canot get better than .25 MOA - hard to do using a
    > hand held sextant.
    > John H.
    > View and reply to this message
    Professor of Applied Mathematics
    University of Manchester

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