File:Epicycle and deferent.svg
Summary
Qualitative <a href="https://en.wikipedia.org/wiki/Deferent_and_epicycle" class="extiw" title="en:Deferent and epicycle">epicycle-and-deferent</a> model as it was used by Apollonius, Hipparcus, Ptolemy and others in order to explain the apparent retrograde motion of planets in a geocentric model. The small circle in the center represents the Earth; the larger circle centered on the Earth is the deferent; the smaller circle centerd on a point of the deferent is the epicycle (its center is highlighted with a black dot in the drawing, but it was no physical body according to ancient astronomers); the filled red dot is the planet, which is centered on a point of the epicycle; the bold black line represents the actual motion of the planet, resulting from the composition of the double revolution of the deferent around the Earth and of the epicycle around a point of the deferent; the empty red dots are consecutive positions of the planet. As seen from the Earth, the planet seems to move forward (eastbound) from 1 to 2, to stop in 2, to move backwards from 2 to 3, to stop again in 3 and then to resume its normal forward motion.
Licensing
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File history
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 10:10, 6 January 2017 | | 560 × 500 (9 KB) | 127.0.0.1 (talk) | Qualitative <a href="https://en.wikipedia.org/wiki/Deferent_and_epicycle" class="extiw" title="en:Deferent and epicycle">epicycle-and-deferent</a> model as it was used by Apollonius, Hipparcus, Ptolemy and others in order to explain the apparent retrograde motion of planets in a geocentric model. The small circle in the center represents the Earth; the larger circle centered on the Earth is the deferent; the smaller circle centerd on a point of the deferent is the epicycle (its center is highlighted with a black dot in the drawing, but it was no physical body according to ancient astronomers); the filled red dot is the planet, which is centered on a point of the epicycle; the bold black line represents the actual motion of the planet, resulting from the composition of the double revolution of the deferent around the Earth and of the epicycle around a point of the deferent; the empty red dots are consecutive positions of the planet. As seen from the Earth, the planet seems to move forward (eastbound) from 1 to 2, to stop in 2, to move backwards from 2 to 3, to stop again in 3 and then to resume its normal forward motion. |
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