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    Re: Lunar Distance in Wikipedia
    From: Frank Reed
    Date: 2007 Sep 19, 01:18 -0400

    Henry H, you wrote:
    "The calculation time to complete this work, exclusive of observation time,
    but including the Longitude work-up was 22-minutes - and I'm a bit rusty.
    Claims that this problem required hours to solve are simply myths."
    
    Yep. And frequently-repeated! It's in Sadler's book. It's in the PBS/Nova
    documentary about longitude. And it's in Sobel. As I noted before, they're
    all getting this number, very likely, from an article published in the
    Transactions of the Royal Society (THE science journal of its era) which
    reported 3 to 4 hour computation times in the days before the Nautical
    Almanac was first published. Those folks spent hours because they had to
    calculate the Moon's true position every time. That's a lot of work!
    
    "When I get the opportunity, it is my intent to publish these observations
    on the List. However, as the accuracy of Longitude obtained is really
    astounding, I am double checking everything before giving George and Frank a
    go at it."
    
    Have you tried running it up using the clearing tool on my web site here:
    http://www.HistoricalAtlas.com/lunars ?
    Click on the link there that says "Clear a Lunar Online". It does the
    standard spherical triangle solution and includes a couple of minor details
    like refractional flattening and the oblateness of the Earth (neither of
    these usually make a lot of difference and you can de-select them if you
    want to see whether they're significant in a particular case). The almanac
    data is tabulated in advance, for the entire preiod from 1750 to 2050, so
    you don't need to input that. You can also download predicted lunar distance
    tables for any day in that period if you wish.
    
    You say that the resulting longitude accuracy is "astounding". I frequently
    find the same thing, and I have seen interested beginners get amazing
    results, too. Alex often gets annoyed when I say that beginners can get good
    results, so it occurs to me that I should qualify this statement from now on
    by noting that these are often people with excellent technical observing
    skills in other fields. I don't grab people off the street and say, "hey
    kid, wanna find yer longitude?" :-) They come to me with a natural interest
    in arcane technical arts like navigation. They're often people with skill in
    amateur astronomy or photography, for example. The sorts of people who can
    align things through an eyepiece in any technical field can pick up a
    sextant for the first time and get an excellent longitude right off the bat.
    My own standard deviation for measured lunar distances is about 0.2 minutes
    of arc so that's about +/-6 minutes in longitude. Not infrequently, the
    error is simply zero (less than 1.5 minutes of longitude to be more
    specific).
    
     -FER
    
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