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    Re: How Many Chronometers?
    From: Frank Reed
    Date: 2009 May 10, 23:44 -0700

    Brad, you wrote:
    "Bruce Stark, when he was contributing to the list, offered a wonderful 
    exposition on how to recover GMT via lunars.  The details are found in a 
    NavList posting whose number I cannot remember.  I did keep a file of it 
    though, and link it herein.  All the way from not knowing any time to GMT! I 
    have not exercised the method and can offer no insight as to how accurately 
    one can recover GMT from it. "
    Uh, now wait a minute. You measure the angle between the Moon and the Sun (or 
    some other celestial body from the list in the almanac). You clear it (some 
    math here but not too bad). Then you interpolate the cleared value between 
    known values of those "lunar distance" angles taken from the almanac where 
    they were printed at three hour intervals of GMT. And that's it. That's all 
    there is to it. Bruce's explanation may have obscured that simplicity. Of 
    course if you then want to get longitude, you need to compare GMT with local 
    time which requires a time sight, but that was a common feature of all 
    navigation in that era, not lunars specifically.
    Incidentally, while reading the 'doc' file you attacheded, I was impressed 
    with the fine description of the time sight which occupies about half of the 
    file (just below Bruce's description). And then I realized, 'well, no wonder 
    I'm impressed --that's MY post.' ;-)
    PS: If you have some text in your notes that you've taken from a list posting 
    and you can't remember where it's from (which message), just go to the search 
    box at fer3.com/arc, drop in a phrase from it, and click Search. You'll 
    almost always find it. Then you can post the link to the original message. 
    Messages before the summer of 2006 have arbitrary message numbers which were 
    not part of the original messages so you should post a full URL if you want 
    to link to one of those posts.
    Navigation List archive: www.fer3.com/arc
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