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 +
They are not great circles! Waldo Tobler Geographer [email protected] http://www.geog.ucsb.edu/~tobler On May 3, 2011, at 2:32 PM, Christos Nüssli wrote: > 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 + > > Le 24.04.2011 18:03, [email protected] a écrit : >> >> 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 >> > Sorry for this late post but I was in Italy during the Easter vacation. > > The notion of "tropic" is something easy to apprehend without deep knowledge > in astronomy. The zone of the earth situated between the 2 tropics is the the > only area where the sun passes, at least, twice a year at the exact zenith > (=exactly perpendicular to the ground - in fact, to a plane tangent to our > sphere). In Europe, we cannot observe the real zenith. > Eratosthenes experimented the exact zenith from the bottom of a dry well at > Aswan (=Syene) and by a comparison with the zenith angle at Alexandria, he > was able to calculate the earth circumference. > My opinion is that Eratosthenes well should have been rather at Amada, today > under the lake Nasser, 180 km south of Aswan, but, anyway, that doesn't make > a big difference for an eye measure. > > Atb > _____________________________ > Christos Nüssli > > ***************************** > Europe Maps - http://www.euratlas.org > _______________________________________________ > 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
