Talk:Copernican heliocentrism

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Contents 1 Accuracy of the Copernican System 2 Phases of Venus 3 Uniform circular motion 4 Sunspots 5 Link to analysis of De revolutionibus

[edit] Accuracy of the Copernican System

The article currently says "Copernicus' system was not experimentally better than Ptolemy's model". For any one planet, a geocentric system with one circular epicycle is exactly equivalent to a heliocentric system with circular orbits. However such a geocentric system allows two parameters for each orbit (the radius of the deferent and the radius of the epicycle) wheras the equivalent heliocentric system has only one parameter per orbit plus one for the system as a whole. On the face of it, under these circumstances, the geocentric system should produce more accurate predictions.

Actualy, both the geocentric and heliocentric systems were more complicated than this. Copernicus allowed more epicycles and Ptolomy allowed non-uniform motion (according to Gingerich). It seems likely to me that the non-uniform motion would still produce more accurate results. Anyone know whether this is true? Rjm at sleepers 07:59, 27 March 2007 (UTC)

[edit] Phases of Venus

This article and Gingerich both assert that observation of the phases of Venus provided a proof of heliocentrism. It seems to me that there would be phases of Venus on a geocentric system as well. Can anyone offer an explanation? Rjm at sleepers 10:17, 27 March 2007 (UTC)

[edit] Uniform circular motion

The most recent revision, which does a good job of tidying the text, has also removed the comment that Copernican heliocentrism reinstated uniform circular motion. I'm not sure why this was removed. Gingerich makes the point that this was why astronomers pursued it prior to Kepler. Pending discussion, I've added a brief comment. Rjm at sleepers 05:31, 21 April 2007 (UTC)

[edit] Sunspots

Pleroma has introduced the idea that Galileo's discovery of sunspots with telescope was a factor in the acceptance of heliocentrism. But, I understood that sunspots had been observed long before the discovery of the telescope and in anycase, they don't contradict geocentrism. Sunspots do strike a blow at the idea that the heavens are unchanging, but so do comets and supernova. Rjm at sleepers 05:44, 21 April 2007 (UTC)

[edit] Link to analysis of De revolutionibus

May I suggest the following (which I wrote): http://jameshannam.com/copernicus.htm . De revolutionibus is a bastard of the book to read and there is very little anaylsis on wikipedia of its contents (beyond a list of books) or the arguments that Copernicus uses to make his points. The suggested article is a reasonably detailled explanation of what Copernicus was doing and howe he got his message across. I think it helps explain the reception of his work. James Hannam 08:44, 17 August 2007 (UTC)

The article is clearly relevant and of high quality, so I've added a link to it under "Further reading" here and at De revolutionibus orbium coelestium. Thanks for noting it. EALacey 09:26, 17 August 2007 (UTC)