Rather, the planets moved forward, and then backward. How could this retrograde motion be explained? Defenders of the geocentric model conceived of the so-called epicycles. In fact, the planets ...

What was most brilliant about this suggestion is that it could explain this apparent retrograde motion of the planets without any epicycles. Instead of a planet actually reversing direction ...

"For Mercury and the inner planets, Copernicus's use of secondary epicycles and the Tusi-couple-like mechanism echoes Ibn al-Shatir's approach. Ibn al-Shatir's Mercury model, with its ...

incorporated a number of circles within circles — epicycles — inside of a planet's path. Some planets required as many as seven circles, creating a cumbersome model many felt was too ...

Around AD 130 Ptolemy produced a hugely influential book, the Almagest, which proposed a series of circular “epicycles” operating on the circles to modify the positions of the planets.

Copernicus, of Poland, felt the Ptolemaic view of the planets traveling in circular orbits around the Earth was over-complicated with many smaller circles, epicycles, needed to explain the ...

Ptolemy and others explained this using a system called epicycles, which had the planets moving in little circles within their greater orbits. [At left: The retrograde motion of Mars. Credit ...

I will then show how to get equivalent positions for the planets as seen from a fixed ... Copernicus dealt with by introducing his own epicycles). According to the biography of Copernicus in ...

ancient philosophers had to embellish circular planetary orbits with smaller circular motions called epicycles. These could account, for example, for the way the planets sometimes seem ...

But astronomy historian Alexander Jones of the ... representing period relations derived by the Babylonians — no epicycles required. Jones is more cautious about this suggestion, although ...