| 21. | The model with epicycles is in fact a very good model of an elliptical orbit with low eccentricity.
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| 22. | Newtonian or classical mechanics eliminated the need for deferent / epicycle methods altogether and produced more accurate theories.
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| 23. | Only after Kepler's refinement of Copernicus'theory was the need for deferents and epicycles abolished.
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| 24. | Shen's hypotheses were similar to the concept of the epicycle in the Greco-Roman tradition,
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| 25. | Most historians of astronomy consider that this two-epicycle model reflects elements of pre-Ptolemaic Greek astronomy.
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| 26. | At around 500 BC, the Greeks invented the idea of epicycles, of circles traveling on the circular orbits.
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| 27. | When scholars applied Ptolemy's epicycles, they presumed that each planetary sphere was exactly thick enough to accommodate them.
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| 28. | Although Copernicus'models reduced the magnitude of the epicycles considerably, whether they were simpler than Ptolemy's is moot.
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| 29. | Ptolemaic model of the spheres for Venus, Mars, Jupiter, and Saturn with epicycle, eccentric deferent and equant point.
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| 30. | In models of the universe that precede Ptolemy, generally attributed to Hipparchus, the eccentric and epicycles were already a feature.
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