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Talk:Geocentric theory (view source)
Revision as of 12:54, November 7, 2008
, 12:54, November 7, 2008explanation of the introduction, answer to RSchlafly
: So how would Ptolemy's theory be any different if he had not made the assumption? What flaws were found in the 1500s? How is it a flaw for Jupiter to have moons or Venus to have phases? Why can't elliptical orbits be explained in a geocentric universe? Ptolemy himself used eccentric orbits. Can you provide some substantiation for any of Samd's edits? [[User:RSchlafly|RSchlafly]] 19:18, 6 November 2008 (EST)
: So how would Ptolemy's theory be any different if he had not made the assumption? What flaws were found in the 1500s? How is it a flaw for Jupiter to have moons or Venus to have phases? Why can't elliptical orbits be explained in a geocentric universe? Ptolemy himself used eccentric orbits. Can you provide some substantiation for any of Samd's edits? [[User:RSchlafly|RSchlafly]] 19:18, 6 November 2008 (EST)
Starting a article on ''Geocentric Theory'' with a dictionary's definition of ''geocentric'' makes as much sense as defining ''relative'' - or even ''special'' - at the beginning of an article on the ''Special Theory of Relativity'', i.e., none.
And you're asking:
*''So how would Ptolemy's theory be any different if he had not made the assumption?'' Well, he '''made''' it. So, what do you want to achieve by such speculations?
*''What flaws were found in the 1500s?'' As stated above, Tycho Brahe made the most accurate observations possible before the invention of the telescope. As he couldn't explain these observations within Ptolemy's theory, he invented the ''Tychonic system'' (in 1583) where the earth is the fixed center of the universe, which the sun and moon revolved, while all other planets revolve around the sun. Historically, this is not seen as a geocentric system. (Heracleides Ponticus had similar ideas in the 4th century BC.)
*''How is it a flaw for Jupiter to have moons or Venus to have phases?''
:#Jupiter moons: In Ptolemy's theory, every movement happens on spheres around the earth. You may argue that the idea of having just one center of movement wasn't central to Ptolemy's theory, but at least his medieval interpreters thought otherwise. Therefore, showing that another center of motions existed was a flaw to them. But more important - in my opinion - are the
:#Phases of Venus: Ptolemy's theory put Venus always between sun and earth, i.e., the center of the epicycle of Venus's movement is thought to be in sync with the movement of the sun, the epicycle itself being placed between sun and earth. So, a full phase of Venus would not be feasible, as this implies Venus standing behind the earth - seen from the sun. The invention of the telescope allowed for observing the full set of phases of Venus, as predicted by Kepler, btw. A massive blow to Ptolemy's theories.
*''Why can't elliptical orbits be explained in a geocentric universe? Ptolemy himself used eccentric orbits'' FWIW, you could describe rectangular orbits in a geocentric universe.
*''Can you provide some substantiation for any of Samd's edits?'' - Yes, and I have done so.
I'd like to stress the point that mine is the conventional view of ''Geocentric Theory'' - or ''Geocentric System'', as to be found in any printed encyclopaedia around the world. Nevertheless, I got to the sources and presented Ptolemy's views to you. Now you should bring up some quotes for your point of view, i.e., that ''Geocentric theory'' only includes to use ''Geocentric coordinates'' - the dictionary reference which you put in the text isn't a valid point, I'm afraid (and yes, it's just a ''dictionary entry'', you'll find a quite similar entry in the dictionary part of the current online edition of the Britannica.)
So I rewrote the introduction. I'm glad if you improve the style, but I'd like you to explain any change of its content on this talk page, first.
--[[User:BRichtigen|BRichtigen]] 07:54, 7 November 2008 (EST)