This is a MapHist list message (when you hit 'reply' you're replying to the whole list) o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o +
The five great circle in the skies were clearly described by Ptolemy in his Almagest, around the middle of the 1st century of our Era (see, for instance, Toomer's edition of the Almagest) and are (1) the ecliptic, (2) the equator, (3 and 4) the two tropics, and (5) the main colure passing through the Vernal point and the poles (equinoctial colure, http://en.wikipedia.org/wiki/Colure). In astronomy they have been for centuries the most important great circles, as it is possible to describe the position of any point in the sky (stars, Moon and planets) according to angular distances from the equator and the colure (equatorial coordinate system) or the ecliptic and its pole (ecliptic coordinate system). Of course, the grid of coordinates are infinite (and infinite are the great circles) but the main great circles, in ancient astronomy, were five! It is not a matter of opinion but it is a matter of History. As I have pointed out several times in my messages to the list, to be Historian means to have a peculiar scientific method to approach the past. It is not sufficient to be able to count up to infinity to write a History of numbers or to know calculus to write a History of Calculus; neither to have a computer machine and use sophisticated softwares to write a History of the Processes of Human Knowledge . . . and so on. As a more clear example I may mention the Science of Philology: to be a literate person is not sufficient to study and understand a Medieval text. Coming to Tom answer, I may suggest to have a look at Statistical dating of the Phenomena by Edoxus, by Dennis Duke (http://www.dioi.org/vols/wf0.pdf) from where I copy the following text: We therefore know that Eudoxus had a fully developed conception of the celestial sphere. He understood the importance of the celestial poles and the celestial equator, and that the path of the Sun – the ecliptic – is a circle inclined to the equator. He understood the tropics as the circles parallel to the equator that touch the ecliptic at its most northern and southern points – the solstices, and when the Sun was at a solsticial point, he knew the fraction of the circumference of a tropic above and below the horizon. He understood the colures as circles through the celestial poles and the solsticial points, and through the celestial poles and the equinoctial points, the points where the equator and ecliptic intersect. . . . At the time of Eudoxus the Tropics appear to be named Winter and Summer Tropics (Eudoxus was active in the first half of the IV century B.C.). Again in the words of Dennis Duke: About the winter tropic, Eudoxus says this: Upon it are: the middle of the Capricorn, . . . The reason why it's been named Tropic of Capricorn is for the constellation of Capricorn is (was) upon it. I have not in my hands (I am on holyday) Otto Neugebauer's HAMA (History of Ancient Mathematical Astronomy) thus I cannot be more precise at the moment, but I am sure you may find there some "correct" reply to your queries. If you may wait for a couple of days I may send you a private message on the matter or supply further bibliography. See, of course, the chapters and related bibliography in the first volume of History of Cartography, edited by Brian Harley and David Woodward (Chicago University Press, 1987). vladimiro Il giorno 24/apr/2011, alle ore 21.11, [email protected] ha scritto: > This is a MapHist list message (when you hit 'reply' you're replying to the > whole list) > o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + > > I cannot answer your question. I will note that there is an infinite count of > great circles on the earth's surface, not" five". > > Regards, > daan Strebe > > > > -----Original Message----- > From: [email protected] > To: History of Maps > Sent: Sun, Apr 24, 2011 9:03 am > Subject: [MapHist] Tropic of Cancer and of Capricocrn > > This is a MapHist list message (when you hit 'reply' you're replying to the > whole list) > o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + o + > > > In my class I was asked when the tropics of Cancer and Capricorn were > identified as two of the five great circles around the earth. Wikipedia has > failed me on the question. Surely these go back before the > Greeks who named them. I would like to impress my students with an answer and > would appreciate whatever you can give me. > The next one will probably be the equinoctial line. (Sigh!) > Tom Goodrich > _______________________________________________ > MapHist: E-mail discussion group on the history of cartography > hosted by the Faculty of Geosciences, University of Utrecht. > The statements and opinions expressed in this message are those of > the author and do not necessarily reflect those of the University of > Utrecht. The University of Utrecht does not take any responsibility for > the views of the author. > List Information: > http://www.maphist.nl > > > Maphist mailing list > > [email protected] > http://mailman.geo.uu.nl/mailman/listinfo/maphist > _______________________________________________ > MapHist: E-mail discussion group on the history of cartography > hosted by the Faculty of Geosciences, University of Utrecht. > The statements and opinions expressed in this message are those of > the author and do not necessarily reflect those of the University of > Utrecht. The University of Utrecht does not take any responsibility for > the views of the author. > List Information: http://www.maphist.nl > > Maphist mailing list > [email protected] > http://mailman.geo.uu.nl/mailman/listinfo/maphist
_______________________________________________ MapHist: E-mail discussion group on the history of cartography hosted by the Faculty of Geosciences, University of Utrecht. The statements and opinions expressed in this message are those of the author and do not necessarily reflect those of the University of Utrecht. The University of Utrecht does not take any responsibility for the views of the author. List Information: http://www.maphist.nl Maphist mailing list [email protected] http://mailman.geo.uu.nl/mailman/listinfo/maphist
