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    Re: Recovering Time by Time Sight
    From: Gary LaPook
    Date: 2012 Dec 18, 09:27 -0800
    We've discussed that method before and it's lesser accuracy but any additional navigational information that you have is useful. I think it is interesting that this method is at the heart of GPS, without it each of our GPS enabled devices would require an expensive atomic clock. The GPS in your phone, wristwatch, etc. has only a relatively inaccurate, cheap, clock and the GPS adjusts the presumed time from that clock to get the LOPs from each satellite to intersect at a point just like adjusting the time to get the moon LOP to cross through the star fix. When it does, you know the time is correct.


    --- On Tue, 12/18/12, Frank Reed <FrankReed@HistoricalAtlas.com> wrote:

    Then there are lunar time sights. Instead of shooting an "actual" lunar distance where we measure the angle between the Moon and the Sun or a star, we can measure the altitude of the Moon and use it for a time sight. The resulting local time should match the local time from a Sun time sight. If it doesn't, you change the assumed GMT until they match. This is, of course, equivalent to plotting a standard LOP for a Moon altitude along with other LOPs (a method independently discovered by a number of 20th century navigators including Letcher and Chichester). If the Moon LOP passes through the fix from the other LOPs, then your GMT is correct. If it passes east or west, then your GMT is wrong, and you adjust it until they match. In order to get a meaningful measure of GMT by this technique, the Moon should be more or less "sideways" in the sky with the horns of the crescent (or the poles at other phases) more or less parallel to the horizon. Though this all works, it's relatively low accuracy.

    Just some thoughts...


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