Ptolemy's The Peculiar Nature Of The Sun

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Ptolemy would say that the Earth is undoubtedly at rest. He makes this claim in The Peculiar Nature of the Universe (Ptolemy 72). To Ptolemy, the idea that earth is stationary and the heavens move is the most obvious and simplest conclusion to draw from celestial observations. Other thinkers formed different hypotheses; some thought that the earth rotated on an axis while the heavens remained at rest, and others claimed that both earth and the heavens move by different amounts (Ptolemy 74). Ptolemy dismisses these contrary ideas, but not without consideration. “For the sake of argument,” he says, he entertains the idea that the earth does in fact rotate (Ptolemy 74). In order for earth to rotate once a day, given its size, the speed of rotation…show more content…
In If a Man Were in the Sky and Could See the Earth Clearly, Oresme defends the idea that the earth is not at rest. He first supplies the opposition to his claim: one can observe all the celestial bodies rising and setting, as well as the revolution of the heavens around the pole star. The rotation of the earth would have to be quick, which would produce strong winds from the east, but there is no such wind. He also cites Ptolemy’s claim that objects propelled upwards would not fall straight back down (Oresme 93). Based on all of these, the earth is at rest. However, Oresme refutes all of these ideas by claiming that all motion is relative. The earth remaining stationary while the heavens revolve around it, or the heavens remaining stationary while the earth rotates can both produce the image of the heavens revolving around earth; this is because “we apprehend movement only insofar as we apprehend the change of a body’s position relative to that of another” (Oresme 94). Additionally, he states that the air and water of the earth moves with the earth, which explains why there is no wind associated with earth’s rotation. This also explains why an object thrown up into the air comes straight back down; the air moves eastward with the earth, and thus propels the object eastward with the air, causing it to land straight down relative to where it was thrown
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