Pythagorus' Spherical Earth

  1. baywax

    baywax 2,215
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    Has anyone else heard of Pythagorus' spherical earth model?

    http://en.wikipedia.org/wiki/Spherical_Earth

    There is a link on this page to a Philosophy out of India that claimed the earth was spherical as well... but I couldn't find it.

    I'm just in awe of these early observations, and find it hard to believe they were lost for so long until only just recently.
     
  2. jcsd
  3. mgb_phys

    mgb_phys 8,952
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    I don't think they were lost, nobody in the years since Hipparchus believed the Earth was flat. Washington Irvine famously wrote a story about Columbus being stopped by the church because the earth was flat - but this story was just a bit of political trouble making.

    On the other hand pythagorus thinking the Earth was a sphere because a sphere is the perfect shape is no more justified than the elephants on the back of a turtle model.
     
  4. baywax

    baywax 2,215
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    Well, we don't know if it was Pythagorus' thinking that came up with earth as a sphere 600 BC. He quite possibly got the idea from earlier documents, the likes of which could have been found at the Library of Alexandria. In fact... 600 years after Pythagorus, Ptolemy based his maps on those of the Phoenician Marinus of Tyre, who in turn drew on even earlier mapmakers for inspiration. Ptolemy lived from around 85 ad to 165 ad and actually had a chance to study the charts in the Library of Alexandria since he lived in Alexandria for most of his life. He never made more than one or two maps of the known world but he brought to Cartography a new system of longitude and latitude which we can guess came from his studies at the library. It was by this system that many maps were calculated and many were quite accurate, to a degree.

    Ptolemy's hypotheses of astronomy

    http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Ptolemy.html

    So I see no reason to assume that Pythagorus came up with the idea of a Spherical Earth on his own. He was also Greek, like Ptolemy and the Greeks were often guests in Egypt as intellectual tourists etc.
     
    Last edited: Aug 18, 2008
  5. baywax, your great start should go on a bit further with the mention of the name of Eratothenes http://en.wikipedia.org/wiki/Eratosthenes who measured the “spherical” Earth’s circumference with real accuracy before 200 BC. Confusion that followed led Columbus to underestimate Earth’s size and discover the New World. http://users.zoominternet.net/~matto/M.C.A.S/notes_size_shape.htm The more precise but not quite complete oblate ellipsoidal shape developed more recently as a part of geodesy. http://en.wikipedia.org/wiki/History_of_geodesy I suspect that we can still get into trouble from oversimplifying the Earth’s shape.
     
  6. baywax

    baywax 2,215
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    Thank you DEMcMillan,

    Its becoming quite disconcerting to find that these great minds, like Ptolemy, were practically permanent fixtures of the Alexandria Library. I get the feeling that they found records of methods for doing and recording geological and astronomical measurements at the library, there, waiting for someone with an open mind to interpret and try out in what was the modern world of the time.

    Ptolemy himself points out that "It is reasonable to assume that the first ideas on these matters came to the ancients from observation such as the following"... here he's refering to the idea that the "heavens" are spherical.

    http://en.wikipedia.org/wiki/Eratosthenes

    What I don't know is exactly what books and papyrus were in the Alexandria Library. Who are the "ancients" that seem to have invented many of the ideas that were eagerly taken up and continued by the Greeks and others who had the opportunity to study there?

    Apparently they spurred quite a movement. Accurate measurements of the distance to the sun from earth, systems of longitude and latitude with compensations for the curvature of the earth, a spherical earth at that.... and so on.

    It was always my impression through elementary and high school that no one figured out the world was a sphere until Marco Polo or even the 1400s. And no one taught anything to the contrary.
     
  7. baywax

    baywax 2,215
    Gold Member

    I'm looking into a bit of the history of the Alexandria Library...

    Here's a good link and some quotes from it..

    So Pythagorus, in 600 BC did not have access to the Library since it was not built in his time. But, he did have access to the Egyptian records. And the Egyptians already had the value of Pi built into their pyramids on the Gaza Plateau. Is this where Pythagorus got the formula?

    Apparently, the relation between the slope of the pyramids and Pi may have simply happened by accident rather than by design... but, that doesn't mean it went unnoticed and unrecorded...

    http://www.math.washington.edu/~greenber/PiPyr.html

    All these quotes: http://www.arabworldbooks.com/bibliothecaAlexandrina.htm

    I don't want to suggest that these librarians and their assistants were too dumb to come up with these calculations and methods on their own, but, it seems just a bit to coincidental that these revolutionary ideas always seem to pop up in Alexandria.

    So far all I know about the contents of the Alexandria Library are that the catalog was called a "Pinakes". The poet Callimachus (another Head Librarian at Alexandria) solved the problem (without the Dewy Decimal System) of cataloging by compiling a catalogue called The Pinakes... or "subject launch pad".
     
    Last edited: Aug 20, 2008
  8. baywax

    baywax 2,215
    Gold Member

    Don't freak out but here's what Wicipedia states is the Earliest model of the Armillary Sphere ( (variations are known as spherical astrolabe, armilla, or armil) is a model of the celestial sphere.).

    http://en.wikipedia.org/wiki/Armillary_sphere

    So... you can see that attributing "the first" to someone is always a gamble because it seems that, whatever the invention, it has been thought of somewhere else with less fan fare.:grumpy:

    PS. "Before the advent of the European telescope in the 17th century, the armillary sphere was the prime instrument of all astronomers in determining celestial positions."...

    but was the 17th Century really the first time period to have a telescope???
     
  9. mgb_phys

    mgb_phys 8,952
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    Even after the invention of the telescope the astrolab was still much better for astrometric (star position) measurements.
    You can make more accurate measurements merely by making the astrolabe bigger, so Tycho's was a basically a building sized sundial - similar to the observatories all over the middle east and india (http://en.wikipedia.org/wiki/Yantra_Mandir)

    Telescopes were distrusted because although they made the stars brighter any faults in the optics could move the position of the star and invalidate your measurements.
    Even today it's hard to make accurate star position measurements with an ordinary telescope eyepiece.
     
  10. baywax

    baywax 2,215
    Gold Member

    I had no idea mgb_phys. That's incredible. Was the Aztec Calendar the same sort of astrological record only flat? Are there examples of the astrolab in the Egyptian or South American cultures? I should have a look for that.
     
  11. mgb_phys

    mgb_phys 8,952
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    I suppose all calenders are flat astronomical records

    I don't know about portable astrolabes.
    The Indian style observatories just need a tower and an angle scale marked on the ground, so aren't difficult to build. To get more accuracy just make a bigger circle! Astrolabes are harder to make since you need to be able to mark a small accurate scale.

    The egyptians certainly had a device like a roman Groma, you just need a wooden cross with 4 strings and you can use the stars to find north. This was used to align pyramids and presumably anything else you want aligned.
     
  12. baywax

    baywax 2,215
    Gold Member

    Sorry, that should read "Mayan" calendar.

    Very interesting stuff.
     
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