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    Re: Lunar refernce
    From: Alexandre Eremenko
    Date: 2006 Apr 11, 19:26 -0400

    Dear Todd,
    The best reference for the lunars is THIS LIST.
    
    There are several books (I know one!) and websites
    on the Lunars, all of them  were extensively discussed
    on this list. The best website (on my opinioon) is
    www.clockwk.com/lunars/
    
    But I hope the Lunars experts forgive me if I include
    
    A VERY SHORT INTRODUCTION TO LUNARS:-)
    
    In XVII century, the most pressing question of the whole science
    was "how to find longitude".
    From the beginning, there were two competing methods:
    1. Making a (very) good clock (chronometer) and
    2. Lunar distances (=Lunars as they are known in English-speaking
    countries).
    (I do not mention many other methods proposed which proved to be
    non-practiceable, at least at sea).
    
    Until the end of XVIII century these two methods seriously
    competed.
    By the end of the 1-st quarter of XIX century chronometers won
    the competition, (because of the simplicity of the chronometer method) but
    Lunars were still used (mainly to check chronometers)
    probably to the beginning of XIX century, occasionally.
    
    From the beginning of 20-s century, chronometers also gradually
    became obsolete, because of the invention of Radio.
    (If you can get time signals few times a day, your wristwatch
    is not worse than the best chronometer).
    
    Still, chronometers were widely used, until 1970-s, and are used to this
    time, at
    least in some countries:-)
    
    So in XX century, the lunars were completely forgotten, not taught
    at schools and no tables to use them were published.
    
    Sometime in the beginning of 1980-s, the whole subject of Cel Nav
    became obsolete "for all practical purposes"
    because of the cheap
    satellite navigation systems.
    
    (But marine people are extremally conservative, they still teach Cel Nav;
    in come countries this is even REQUIRED to obtain certain licences.
    In some countries, sextants and chronometers are still required on every
    commercial
    ship:-)
    
    A strange thing happened in the end of 1990-s.
    Some people decided to revive this ancient Lunars method.
    Why not? There are people who like to do all sorts of non-profit,
    non-commercial activities:-) Who sail, who collect ancient furniture,
    or ancient steam engines, chronometers, sextants etc., and even wish
    to USE these things.
    
    So they revived this almost completely forgotten method of
    Lunar distances.
    
    2. The essence of the method. You want to know the TIME.
    Some absolute time not related to your longitude.
    You have to use some celestial phenomenon which will give you
    this absolute time. But the sky does not change much.
    (Except the daily rotation which gives you relative, local time.)
    There are essentially two phenomena in the sky which can be observed
    inbdependently of your longitude, and which change quickly enough to
    help you determine the time. These are the Moon motion with
    respect to the stars and the motion of Jupiter satellites.
    Jupiter satellites are better if you are on land, and not in a hurry,
    and have a powerful telescope, installed on a firm foundation.
    
    Moon is preferable if you are at sea.
    
    Resume.
    Lunar distances is a method of determinimg your position
    WITHOUT knowing time.
    
    You can scan this list archive for more info,
    or to go dtraight to the web site mentioned above.
    
    Alex.
    
    
    

       
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