The Motions of the Earth
Anyone who thinks that Copernican theory is “simpler” than Ptolemaic theory has never looked at Book III of De revolutionibus. In a geocentric system the earth is at rest—as indeed it appears to be—and any apparent motions in the heavens that we know to result from its motions are distributed among a number of objects, i.e. the sun, the individual planets, the sphere of the fixed stars, everything in its proper place as it actually appears. But when Copernicus worked through the consequences of his own theory, he had to attribute to the earth no less than three fundamental motions and a number of secondary motions. That all these compounded motions forced upon a single and, to all appearances, quiescent body seemed implausible to his contemporaries is not to be wondered at, especially because the end result was nothing other than reproducing the same apparent motions in the heavens that had been accounted for all along (and without making asumptions that contradicted contemporary natural philosophy, common sense, and the most casual or most meticulous observations then possible of the behavior of the earth and of objects on or near its surface).
KeywordsSummer Solstice Star Catalogue Vernal Equinox Maximum Equation Apparent Time
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