• At the time of Ptolemy, the introduction of epicycles was considered a very elegant idea because it explained the motion of the planets to the accuracy observable at the time.
• it was consistent with the prevailing geocentric world view.
• it explained the apparently irregular motion of the planets in the sky with “perfect” circles.
• because it did not openly contradict the teaching of the previous authorities.
• All of the above.
New (and correct) explanation f Retrograde (westward) motion of a planet occurs when the Earth passes the planet.
or retrograde motion of the planets: This made Ptolemy’s epicycles unnecessary Described in Copernicus’ famous book “De Revolutionibus Orbium Coelestium” (“About the revolutions of celestial objects”)
• In the Copernikan “Universe”, the orbits of pl anets and moons were … Perfect Circles
• None of the above.
Used the precise observational tables of Tycho Brahe (1546 – 1601) to study planetary motion mathematically. Found a consistent description by abandoning both
Planets move around the sun on elliptical paths, with non-uniform velocities
The orbits of the planets are ellipses with the sun at one focus.
Eccentricities Orbits of planets are virtually indistinguishable from circlesof planetary orbits
A line from a planet to the sun sweeps over equal areas in equal intervals of time.
• Are all four seasons equally long? Yes.
• No, summer is the longest; winter is the shortest.
• No, fall is the longest; spring is the shortest.
• No, winter is the longest; summer is the shortest.
• No, spring is the longest; fall is the shortest.