What is the meaning of the word epicycle?
Definition of epicycle. 1 in Ptolemaic astronomy : a circle in which a planet moves and which has a center that is itself carried around at the same time on the circumference of a larger circle. 2 : a process going on within a larger one. Other Words from epicycle Example Sentences Learn More about epicycle.
What is epicyclic theory in astronomy?
Epicyclic theory, in part, sought to explain this behavior. The inferior planets were always observed to be near the Sun, appearing only shortly before sunrise or shortly after sunset. Their apparent retrograde motion occurs during the transition between evening star into morning star, as they pass between the Earth and the Sun.
What is the deferent/epicycle device used for?
The deferent (O) is offset from the Earth (T). P is the centre of the epicycle of the Sun S. Ptolemy's and Copernicus' theories proved the durability and adaptability of the deferent/epicycle device for representing planetary motion.
What is Epicyclical motion?
Epicyclical motion is used in the Antikythera mechanism, an ancient Greek astronomical device for compensating for the elliptical orbit of the Moon, moving faster at perigee and slower at apogee than circular orbits would, using four gears, two of them engaged in an eccentric way that quite closely approximates Kepler's second law .
What is an epicycle supposed to explain quizlet?
Epicycle. The small circle followed by a planet in the Ptolemaic theory. The center of this follows a larger circle (the deferent) around Earth. Deferent. In the Ptolemaic theory, the large circle arond Earth along which the center of the epicycle was thought to move.
What is Ptolemy epicycle supposed to explain?
In order to explain the motion of the planets, Ptolemy combined eccentricity with an epicyclic model. In the Ptolemaic system each planet revolves uniformly along a circular path (epicycle), the centre of which revolves around Earth along a larger circular path (deferent).
What is the epicycle in the Greek planetary model?
small circle through which the planet moves as the center of this circle orbits Earth.
How did the Ptolemaic model explain?
He argued that planets move on two sets of circles, a deferent and an epicycle. This explained retrograde motion while keeping the planets in their circular orbits around the Earth. Where this did not fit, Ptolemy proposed an eccentric.
What is the Ptolemaic view of the universe?
Based on observations he made with his naked eye, Ptolemy saw the Universe as a set of nested, transparent spheres, with Earth in the center. He posited that the Moon, Mercury, Venus, and the Sun all revolved around Earth.
What is the problem with epicycles?
The problem is that the epicycle containing Mercury, the epicycle containing Venus, and the Sun all orbited around the Earth in one year! So their order was reluctantly agreed upon because Mercury moved fastest on it epicycle, Venus next fastest, and of course the Sun had no epicycle (because it never retrograded).
How does epicycle differ from deferent?
revolved around small circles called epicycles at a uniform rate while the centre of the epicyclic circle orbited Earth on a large circle called a deferent. Other variations in the motion were accounted for by offsetting the centres of the deferent for each planet from Earth by a short distance.…
What is the epicycle used for?
In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (from Ancient Greek: ἐπίκυκλος, literally upon the circle, meaning circle moving on another circle) was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets.
Why is adding epicycles bad science?
Bad science. In part, due to misunderstandings about how deferent/epicycle models worked , "adding epicycles" has come to be used as a derogatory comment in modern scientific discussion. The term might be used, for example, to describe continuing to try to adjust a theory to make its predictions match the facts.
How are the epicycles related to Ptolemy's Sun?
That means that all the bodies revolve in their epicycles in lockstep with Ptolemy's Sun (that is, they all have exactly a one-year period).
What was Copernicus's problem with the Sun-centered positions?
The Sun-centered positions displayed a cyclical motion with respect to time but without retrograde loops in the case of the outer planets. In principle, the heliocentric motion was simpler but with new subtleties due to the yet-to-be-discovered elliptical shape of the orbits. Another complication was caused by a problem that Copernicus never solved: correctly accounting for the motion of the Earth in the coordinate transformation. In keeping with past practice, Copernicus used the deferent/epicycle model in his theory but his epicycles were small and were called "epicyclets".
Why did Ptolemy and Copernicus use the deferent/epicycle model?
The deferent/epicycle models worked as well as they did because of the extraordinary orbital stability of the solar system.
Why did the ancients use geocentric theory?
The ancients worked from a geocentric perspective for the simple reason that the Earth was where they stood and observed the sky, and it is the sky which appears to move while the ground seems still and steady underfoot. Some Greek astronomers (e.g., Aristarchus of Samos) speculated that the planets (Earth included) orbited the Sun, but the optics (and the specific mathematics – Isaac Newton 's Law of Gravitation for example) necessary to provide data that would convincingly support the heliocentric model did not exist in Ptolemy 's time and would not come around for over fifteen hundred years after his time. Furthermore, Aristotelian physics was not designed with these sorts of calculations in mind, and Aristotle 's philosophy regarding the heavens was entirely at odds with the concept of heliocentrism. It was not until Galileo Galilei observed the moons of Jupiter on 7 January 1610, and the phases of Venus in September 1610 that the heliocentric model began to receive broad support among astronomers, who also came to accept the notion that the planets are individual worlds orbiting the Sun (that is, that the Earth is a planet and is one among several). Johannes Kepler was able to formulate his three laws of planetary motion, which described the orbits of the planets in our solar system to a remarkable degree of accuracy; Kepler's three laws are still taught today in university physics and astronomy classes, and the wording of these laws has not changed since Kepler first formulated them four hundred years ago.
Is there a trace of multiple epicycles?
As it turns out, a major difficulty with this epicycles-on-epicycles theory is that historians examining books on Ptolemaic astronomy from the Middle Ages and the Renaissance have found absolutely no trace of multiple epicycles being used for each planet. The Alfonsine Tables, for instance, were apparently computed using Ptolemy's original unadorned methods.