File:Epicycle and deferent.svg

From Wikimedia Commons, the free media repository
Jump to navigation Jump to search
Original file(SVG file, nominally 560 × 500 pixels, file size: 9 KB)


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.
Source Based upon data from Thomas S. Kuhn, La rivoluzione copernicana (The Copernican Revolution), Einaudi, Torino, 2000, p. 78. Also based upon File:Epicycle et deferent.png by Julo
Author Own work MLWatts
Other versions

File:Epicycle et deferent.png by Julo


PD-icon.svg This file 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.

File history

Click on a date/time to view the file as it appeared at that time.

current16:50, 27 June 2013Thumbnail for version as of 16:50, 27 June 2013560 × 500 (9 KB)MLWatts (talk | contribs)Corrected eastbound direction as seen from top of the Earth's North Pole
16:40, 27 June 2013Thumbnail for version as of 16:40, 27 June 2013560 × 500 (9 KB)MLWatts (talk | contribs)User created page with UploadWizard
  • You cannot overwrite this file.

There are no pages that link to this file.

File usage on other wikis

The following other wikis use this file: