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    Re: Early lunars
    From: George Huxtable
    Date: 2010 Mar 21, 10:19 -0000

    Wolfgang , under threadnames "Sobel and longitude", and "Early lunars", has 
    provided useful information about Columbus and his attempts to determine 
    his position in Jamaica.
    
    I've riffled through my own shelves, and rather to my surprise have 
    discovered six books dealing with Columbus. A surprise because I'm no fan 
    of Columbus. He was an incompetent navigator. And he  has a lot to answer 
    for.
    
    The eclipse, of the Moon,  happened on 29 Feb 1504, on Columbus' fourth 
    voyage, when he was marooned in Jamaica. Columbus tells us how he used the 
    predicted event to impress the native Indians with his powers.
    
    One volume, "The voyages of Christpher Columbus", by Cecil Janes (1930) 
    doesn't mention the event at all.
    
    Another, "Columbus in the age of discovery", by Zvi Dor-Ner (1992), seems 
    to be more about the author and his TV productions than about Columbus. He 
    states that Columbus took his eclipse data from a Nuremberg Almanac, and 
    pictures the entry about eclipses, which I attach, from Regiomontanus' 
    Calendarium.
    
    Bjorn Landstrom's "Columbus", 1966, derides the longitude derived by 
    Columbus from the eclipse, which, as he says, would have placed him way out 
    in the Pacific, but approves of the latitude observation, which we will 
    consider.
    
    "The life of the Admiral Christopher Columbus, by his son Ferdinand", 
    (trans. Keen 1960) deals only with the impressing-the-natives story, as 
    does Alexander McKee, in "A World too Vast" (1990), though there he states 
    that the eclipse prediction came from Abraham Zacuto.
    
    The only real meat, then, is provided in Morison's "Admiral of the Ocean 
    Sea", of 1942, and I attach the relevant page for  Columbus' words to be 
    assessed. On another page, Morison tells us that the eclipse prediction was 
    from Regiomontanus' Ephemerides, "printed at Nuremberg before the end of 
    the century, but containing predictions for 30 years ahead". I have 
    attached what Morison wrote about the finding of longitude and latitude 
    (when marooned at Santa Gloria, taken to be St Ann's Bay, roughly in the 
    middle of the North coast of Jamaica).
    
    Can anyone make any sense of the way Columbus deduced that the ending of 
    the eclipse "when the moon had just returned to its light" (whatever that 
    may mean, in terms of the phase of the eclipse), two hours and a half after 
    sunset, implied a longitude difference of seven hours and fifteen minutes 
    from Cadiz, whereas that difference is more like four hours and forty 
    minutes. Wolfgang has suggested that Columbus hadn't realised that the 
    prediction was given for Nuremberg, but even that would imply a longitude 
    difference of less than six hours.
    
    As for the latitude, what Columbus tells us is inadequate. In that era, 
    Polaris was best part of 4 degrees from the Pole, and so it was vital to 
    allow for it, done by looking at the position of the Guards, a pair of 
    pointer stars, with respect to a mythical figure, usually that of a naked 
    man, standing upright in the Pole sky with Polaris at his navel. (For 
    understandable reasons, many navigators from Latin lands preferred to see 
    the figure of a naked woman).
    
    All Columbus tells us is that "the Guards were on the arm", without telling 
    us which arm. And it's important. David Waters, in "The art of 
    navigation..." (1958) quotes "Regimento do astrolabio e do quadrante", 
    dated 1509? as saying "When the Guards are on the West Arm the North Star 
    stands above the Pole one degree and a half", and presumably vice versa 
    when the Guards are on the East Arm. Columbus doesn't say which, though we 
    could easily check for ourselves in a planisphere program, and check the 
    eclipse details too: I haven't done so. Any refraction corrections in 
    altitude are negligible in view of the low accuracy of Columbus' 
    observations.
    
    Morison has simply compared latitude with altitude, and found them to be 
    half-a-degree apart, without (apparently) allowing for Polaris, and deduced 
    that Columbus could observe to half a degree. Morison may have been a good 
    historian, but not a navigator.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message ----- 
    From: "Wolfgang K�berer" 
    To: 
    Sent: Saturday, March 20, 2010 2:47 PM
    Subject: [NavList] AW: Re: AW: Early lunars
    
    
    According to Maddison ("Medieval scientific instruments and the development
    of navigational instruments in the XVth and XVIth centuries", 30) the
    nocturnal was first described by Ram�n Llull by the end of the XIIIth
    century, but this is based on an edition of 1721 and I would not place too
    much faith in it.
    Hester Higton ("Sundials at Greenwich", 387) also states that nocturnals
    were in use "by at least the tenth century"; she does not give any
    reference, though.
    Finally G�nther Oestmann has written an article in the SIS-Bulletin (No. 
    69,
    5 - 9) on the history of the nocturnal and says that there must have been
    forerunners of the instrument that early and that - in contrast to the
    astrolabe - manuscripts on this type of instrument are rare; only 18
    manuscripts describing the use and manufacture from the 15th and 16th
    century are known to him.
    
    Wolfgang
    
    
    
    
    
    
    
    
    

       
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