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Talk:Geocentric theory (view source)
Revision as of 16:05, November 5, 2008
, 16:05, November 5, 2008→Ptolemy's view of a stationary earth: new section
:::::::::::: No. What is the difference? Can you point to some advocate of geocentric theory who relied on that difference? [[User:RSchlafly|RSchlafly]] 14:28, 4 November 2008 (EST)
:::::::::::: No. What is the difference? Can you point to some advocate of geocentric theory who relied on that difference? [[User:RSchlafly|RSchlafly]] 14:28, 4 November 2008 (EST)
::::::::::::: You didn't say ''what'' the Earth is supposed to be at the centre of, but let's say that one thing that it's supposed to be at the centre of is the solar system. Yet most people do not agree with the idea that the Earth is at the centre of the solar system. But that doesn't stop those same people using co-ordinates based on the Earth (geocentric co-ordinates) when appropriate. That's the difference (well, one way of explaining it). [[User:Philip J. Rayment|Philip J. Rayment]] 21:15, 4 November 2008 (EST)
::::::::::::: You didn't say ''what'' the Earth is supposed to be at the centre of, but let's say that one thing that it's supposed to be at the centre of is the solar system. Yet most people do not agree with the idea that the Earth is at the centre of the solar system. But that doesn't stop those same people using co-ordinates based on the Earth (geocentric co-ordinates) when appropriate. That's the difference (well, one way of explaining it). [[User:Philip J. Rayment|Philip J. Rayment]] 21:15, 4 November 2008 (EST)
== Ptolemy's view of a stationary earth ==
RSchlafly asked me:{{quotation|Where does Ptolemy explain why he put the earth in the center? In the Almagest or elsewhere? Where does Ptolemy make the distinction in point 2? [i.e., the earth is the single center of motion]}} and
{{quotation| Does Ptolemy actually say that the Earth is unmovable? Where? In the Almagest? Is it an essential part of his theory?
It may have been natural to rely on Plato and Aristotle, but there were other Greeks who subscribed to a Sun-centered view. Is there some proof that Ptolemy was persuaded by Aristotle's arguments? }}
I'd some time to elaborate my answers, so I looked into the ''Almagest''. As my Greek isn't good enough, and the Latin translations are often described as unsatisfactory, I took the translation of Karl Manitius (1902). I'm told that Toomer's translation into English is excellent (I'll check it out tomorrow), so you'll prefer to go with it.
*''Where does Ptolemy explain why he put the earth in the center? ''
Almagest, First Book, Chapter V:
'''The earth is placed in the middle of the celestial sphere'''
Here, Ptolemy explains that the only position of the earth in the universe which is consistent with all observations is in the center of this universe, ''as in the center of a sphere''.
*''Does Ptolemy actually say that the Earth is unmovable? ''
Almagest, First Book, Chapter VII:
'''The earth has no movement in space'''
Here, Ptolemy not only shows that the earth has a fixed place in space, but he proves that it cannot rotate....
Though Ptolemy doesn't mention Plato or Aristotle, he uses some of their arguments.
Please, do not misunderstand me: Ptolemy was a great scientist. His arguments in these special cases may sound ridiculous to us, but only because other great scientists have refuted them. Often, we're only presented a caricature of those outdated theories, drawn by their victorious enemies. Ptolemy did first-rate mathematics, his models were accurate enough for over a thousand years, and his reasoning compelling enough to convince the greatest thinkers of centuries. But he was very wrong.
--[[User:BRichtigen|BRichtigen]] 11:05, 5 November 2008 (EST)