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    Lunar eclipses and other things
    From: Alexandre Eremenko
    Date: 2004 Oct 26, 18:32 -0500

    1. Contrary to some messages on this list,
    the moon eclipse will occur not "tonight" but
    TOMORROW night. That is on October 27 for most
    of the US and at small hours October 28 in Europe.
    
    2. I want to use this opportunity to pay tribute to some
    people whose efforts made the very business of
    Cel Nav possible at all,
    and
    who are rarely mentioned on this list.
    
    The idea of using Moon eclipses to find longitude
    is credited to
    HIPPARCHUS, who probably was the greatest astronomer
    of all times, and possibly, one of the greatest mathematicians.
    He lived in II century BC.
    We know almost nothing about his life,
    and none of his original writing survives.
    Ptolemy calls him "a hard-working man, and an admirer of Truth".
    
    Most of our knowledge about him
    comes from the references in the books of Ptolemy,
    but Ptolemy was writing
    300 years after Hypparchus.
    
    (The time span is like the time span between Newton and us!)
    
    Hypparchus own astronomical observations, referred by
    Ptolemy permit to establish the time when Hipparchus lived,
    by applying the Lunar theory of Hipparchus backwards in time:-)
    
    (So he built a good memorial for himself, did not he?:-)
    
    90% of our knowledge about Moon motion was known to Hypparchus.
    (part of it is apparently due to "Chaldeans" of whom we know
    nothing).
    
    Most of this theory was derived by Hypparchus by careful
    reduction of the eclipse observations of Chaldeans and of
    hismelf.
    
    The method of finding longitude by the eclipses of the Moon
    (and Sun) remained the ONLY method of finding longitude for
    almost 20 centuries!
    
    This was the only method Columbus could use.
    (Though he was not very successfull with this,
    due to the general collapse of knowledge and educcation,
    which came soon after
    Ptolemy and lasted for about 1500 years).
    This was also the only practiceable method on land,
    to make geographic maps. (The direct measurements of distances
    on land was VERY imprecise).
    
    Hipparchus theory of the Moon motion was not superceeded
    until Tycho Brahe (XVI cent AD), who added a correction term
    of 40' amplitude.
    Neither Copernicus, nor Kepler added much to the Lunar theory
    in the sense of prediction of the Moon motion.
    
    Only due to Newton's mechanics further improvements became
    possible. However, Newton himself failed to explain the
    known irregulatities in the Moon motion. He could not
    overcome the mathematical difficulties. The whole gravitation
    theory was seriously questioned because of this faillure.
    
    It is only due to the efforts of the great Euler and Claiaut that
    approximately in 1750-s the Moon motion was shown to
    be consistent with and explainable by the Newton mechanics.
    (Euler was found eligible for 300 pounds of the Longitude Prize,
    and Meyer who actually developed the tables based on Euler's
    theory got 3000 pounds. More precisely, these 3000 pounds were
    delivered to Meyer's widow:-(
    
    3. This story confirms the sad truth that only the people who
    made the very last step in certain invention are recognized and
    remembered, no matter how relatively small
    their contribution could be. The real giants, to whom we owe
    most of our knowledge, tend to be forgotten.
    This tendency in increasing in our time, with general
    decline of interest to history, and I afraid, to science itself.
    For example Norie (1828) mentions people like Hipparchus,
    Mercator and Newton (and Newton is always endowed with an epitet
    like "immortal". You won't find this in the modern version of
    Bowdich:-)
    
    Alex.
    
    
    

       
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