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Re: Early lunars
From: John Huth
Date: 2010 Mar 21, 06:35 -0400
From: John Huth
Date: 2010 Mar 21, 06:35 -0400
George -
Prior to writing that book, Morrison sailed on several routes Columbus undertook. As an historian he went to some lengths to "test out" many of the routes of early Europeans, which is more than a lot of historians did. I'm pretty sure that Morrison did his own navigation during these trips.
I don't have the book in front of me - I'm currently working in Geneva. From what I recall in the earlier chapters of the book, he (Morrison) illustrates how to use the shoulders etc of the guard stars and I think he's pretty consistent. For me, I use the direction toward Cassiopeia as my mnemonic for making the 42 minute correction.
Morrison would probably agree that Columbus wasn't terribly good at celestial navigation. He was quite skillful at dead reckoning, however. From what I can tell, celestial navigation was really in its infancy at that time, and the use of sightings was more of curiosity than anything.
If you read earlier - in Morrison's book, there's a passage about his third voyage. Columbus was becalmed in the doldrums, and did a series of quadrants sights on Polaris. I think one of the sightings didn't make any sense whatsoever, and rather than dismissing the sighting, he speculated that the Earth had a bulge to it in the middle of the Atlantic. He (Columbus) was definitely a strange character, and I think most of his celestial navigation was, in effect, trying out something new that he didn't have a lot of experience with.
Also, yes, Morrison says that the lunar eclipse put him somewhere in the Pacific, but since Columbus was himself convinced about certain misconceptions about his location, the longitude value he got reinforced his notions. He wasn't much of a scientist, that's for sure, but give him credit for trying it out.
Best,
John H.
On Sun, Mar 21, 2010 at 6:19 AM, George Huxtable <george@hux.me.uk> wrote:
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 Köberer" <koeberer@navigationsgeschichte.de>
To: <NavList@fer3.com>
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 Ramón 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 Günther 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