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| DescriptionEpicycle and deferent.svg |
English: Qualitative epicycle-and-deferent 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.
Italiano: Modello epiciclo-deferente qualitativo. Modelli di questo tipo vennero impiegati da Apollionio, Ipparco, Tolomeo e altri per spiegare i moti retrogradi apparenti dei pianeti nei sistemi astronomici geocentrici. Il piccolo cerchio vuoto al centro rappresenta la Terra; il cerchio più ampio, centrato nella Terra, è il deferente; il cerchio più piccolo, centrato su un punto del deferente, è l'epiciclo (il suo centro è evidenziato con un punto nero nel disegno, ma ad esso non corrispondeva alcun punto fisico nelle concezioni astronomiche degli antichi); il cerchio rosso pieno è il pianeta, che è centrato su un punto dell'epiciclo; la linea nera spessa rappresenta il moto effettivo del pianeta, che risulta dalla composizione della doppia rivoluzione del deferente intorno alla Terra e dell'epiciclo intorno a un punto del deferente; i punti rossi vuoti rappresentano le successive posizioni del pianeta: visto dalla Terra, esso sembra muoversi in avanti (in direzione est) da 1 a 2, fermarsi in 2, muoversi di moto retrogrado da 2 a 3, fermarsi di nuovo in 3 e poi riprendere il suo moto normale.
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| Date | |
| Source | Based upon data from Thomas S. Kuhn, La rivoluzione copernicana (The Copernican Revolution), Einaudi, Torino, 2000, p. 78. Also based upon Epicycle et deferent.png by Julo |
| Author | Own work MLWatts |
| Other versions | Epicycle et deferent.png by Julo |
| SVG development InfoField |
This trigonometry was created with Inkscape…important. 
This trigonometry uses embedded text/digits. |
| Public domainPublic domainfalsefalse |
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This work is ineligible for copyright and therefore in the public domain because it consists entirely of information that is common property and contains no original authorship. |
| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 16:50, 27 June 2013 | | 560 × 500 (9 KB) | MLWatts | Corrected eastbound direction as seen from top of the Earth's North Pole |
| 16:40, 27 June 2013 |  | 560 × 500 (9 KB) | MLWatts | User created page with UploadWizard |
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| Width | 560 |
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| Height | 500 |
