Two competing models attempt to explain the motions and changing brightness of the planets: ptolemy's geocentric model and copernicus' heliocentric model.

sort the characteristics according to whether they are part of the geocentric model, the heliocentric model, or both solar system models.

drag the appropriate items to their respective bins.

epicycles and deferents explain planetary motion.
planets move in circular orbits and with uniform motion.
the brightness of a planet increases when the planet is closest to earth.
this model is earth-centered.
this model is sun-centered.
retrograde motion is explained by the orbital speeds of planets.
retrograde motion is explained by epicycles.
epicycles and deferents explain planetary motion. selected

dragable

geocentric:

heliocentric:

both geocentric and heliocentric: