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If observed from one night to the next, a planet appears to move from West to East against the background stars most of the time. Occasionally, however, the planet's motion will appear to reverse direction, and the planet will, for a short time, move from East to West against the background constellations. This reversal is known as retrograde motion.

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Vada Boyer

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2y ago
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14y ago

If observed from one night to the next, a planet appears to move from West to East against the background stars most of the time. Occasionally, however, the planet's motion will appear to reverse direction, and the planet will, for a short time, move from East to West against the background constellations. This reversal is known as retrograde motion.

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13y ago

Ptolemy did something truly amazing. He developed a way of accounting for retrograde motion built on the idea that some planets orbit the earth not in simple 'circles' (his model is built on circular orbits and not eliptical orbits), but along circular orbits the center of which would mark out a circular orbit around earth. This is hard to follow; see the animated demonstration at the link below. He believed that it was the task of astronomy to define the movements of all the 'wandering' stars [planets] using nothing but circles. He incorporated some other ingenius mechanisms, like having the earth move away from the center of a planet's orbit, to account for the speeding up and slowing down of the planets in their orbits.

The amazing part is that the model worked so well [in terms of location, not distance] that the mechanics of some planetariums is based upon it.

This is a stunning example showing that even the most brilliant people can be convinced that a model must reflect reality because there is tight correspondence, or correlation, between the model and field observations. It also demonstrates that inductive reasoning, while important, cannot be relied upon to have the strength of properly applied deduction. For that matter, even what we convince ourselves to be deduction can reveal an inductive weakness now and then.

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14y ago

By epicycles, small circular "side loops" on the main circular orbit.

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14y ago

The planets moved along small circles that moved on larger circles around the Earth.

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Q: How did the Ptolemaic view of the universe explain retrograde motion?
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How did the Ptolemaic model of the universal explain retrograde motion?

If observed from one night to the next, a planet appears to move from West to East against the background stars most of the time. Occasionally, however, the planet's motion will appear to reverse direction, and the planet will, for a short time, move from East to West against the background constellations. This reversal is known as retrograde motion.


The apparent westward movement of a planet is known as?

retrograde motion


Why was retrograde motion important in astronomy?

Retrograde motion important in astronomy because it helped to explain that the planets revolved around the Sun. Retrograde motion is the ability of some objects to rotate in a direction that is opposite what is expected.


Why did Eudoxus create his solar system to explain what phenomenon?

retrograde motion


Describe what produces the retrograde motion of mars. what geometric arrangement did Ptolemy use to explain this motion?

Earths faster motion makes Mars appear to be going backwards, the backwards motion, in fact, is what caused retrograde motion. --Ptloemy used Epicycles to explain how geocentrical models worked.


Purpose of using epicycles and deferents to explain the motion of the planets in the night sky was to account?

retrograde motion


How did Copernicus explain the retrograde motions of the planets?

All the models explain retrograde motion because it is such an obvious phenomenon. In Copernicus's model an outer planet goes into retrograde motion when the inner planet overtakes it so that it appears from the inner planet to be going backwards along the ecliptic.


What planet was used to explain retrograde motion?

Retrograde motion is motion in the opposite direction. In the case of celestial bodies, such motion may be real, defined by the inherent rotation or orbit of the body, or apparent, as seen in the skies from Earth.


Major advantage of Copernicus' Sun-centered model over the Ptolemaic model?

It offered more natural explanation for the apparent retrograde motion of planets in our sky.


What are the contributions of Eudoxus in geocentric theory?

He created a model for the universe that explained retrograde motion if Earth was at the centre.


Why did the model of the universe proposed by Copernicus gain support after its publication?

It was a more elegant explanation of retrograde motion.


How does each of the models of the universe explain the retrograde motion of planets?

This is nothing as complicated as "models of the universe"... it is a geometric phenomenon. For example, if an outer planet - outside the Earth's orbit - is retrograde, that simply means that Earth is overtaking that planet; temporary the planet seems to go "backwards".The main movement of planets is from West to East; but for part of each orbit, each planet will have an (apparent) movement from East to West - then it is said to be "retrograde".