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Talk:Geocentric theory (view source)
Revision as of 21:29, November 6, 2008
, 21:29, November 6, 2008earth in the center of the heavens is a main point for Ptolemy
: You are right, Ptolemy does say in the Almagest that the Earth is stationary and at the center of the universe. But he bases it mostly on terrestial arguments and acknowledges that others hold a different view.
: You are right, Ptolemy does say in the Almagest that the Earth is stationary and at the center of the universe. But he bases it mostly on terrestial arguments and acknowledges that others hold a different view.
: I just don't see how this supports Samd's edits. Ptolemy did not assume that Earth lies at the center of the universe. He expressed an opinion about it. It is not clear whether the opinion is essential to his theory. [[User:RSchlafly|RSchlafly]] 15:42, 6 November 2008 (EST)
: I just don't see how this supports Samd's edits. Ptolemy did not assume that Earth lies at the center of the universe. He expressed an opinion about it. It is not clear whether the opinion is essential to his theory. [[User:RSchlafly|RSchlafly]] 15:42, 6 November 2008 (EST)
I won't quote the whole of book I, chapter 5 '''That the Earth Is in the Middle of the Heavens''', but here's the very beginning:
{{quotation|Now with this done, if one should next take up the question of the earth's position, the observed appearances with respect to it could only be understood if we put it in the middle of the heavens as the centre of the sphere [...]}}
This, he elaborates at length. ''Heavens'' is here what we would see as ''Universe''. His arguments aren't that much terrestrial. His basic idea is that the heavy bodies tend to the middle of the heavens, so, earth as the heaviest body is in this center. The lighter ones tend to the brim of the heavens, so stars have to be lighter. There is no ''relativistic'' aspect in this concept, the earth and the other bodies are not exchangeable.
Well, he acknowledges the opinions of others only to make fun of those ideas.
*''Ptolemy did not assume that Earth lies at the center of the universe.'' - yes, he did.
*''He expressed an opinion about it.'' - Ptolemy thought that he had proved it. So, it's more than an opinion.
*'' It is not clear whether the opinion is essential to his theory.'' - This ''opinion'' isn't just essential to his theory, it is one of the cornerstones of his theory. It's one of the ''beginning and foundations'' he rests his arguments on, we'd call it one of his axioms.
He outlines these in Book I, Ch. 2, by the way:
{{quotation|And so, in general, we have to state that the heavens are spherical and move spherically; that the earth, in figure, is sensibly spherical also when take as a whole; in position, lies right in the middle of the heavens, like a geometrical centre; in magnitude, has the ratio of a point with respect to the sphere of the fixed stars, having itself no local motion at all.}}
So, for the record:
*Ptolemy knew the ideas of Plato and Aristotle. He refers to these as ''the observations of the ancients''
*Ptolemy belittled the idea of a rotating ore moving earth
*his model is truly geocentric: the earth lies unmovable in the middle of the heavens, all movements take place around it
That's much more than just using geocentric ''coordinates'': It's obvious that you can use geocentric ''coordinates'' to show the movement of the sun relatively to the earth. It's absolutely possible to describe the movement of Venus in geocentric ''coordinates'' - it's just a little bit clumsy.
But you can't integrate both of them in a geocentric ''theory'' the way Ptolemy did it - there spheres would smash...
So, we should not talk just about ''coordinates'', and therefore, Samd's entry is the better one.
--[[User:BRichtigen|BRichtigen]] 16:29, 6 November 2008 (EST)