What device/s did Ptolemy use to explain retrograde motion?
buildToggle(‘a12’); Answer Ptolemy used a combination of epicycles and deferents to explain retrograde motion. The diagram below shows this: A planet orbits point x in a circular path called the epicycle. The deferent is the circular path that point x takes around the centre of motion, C. Credit: R. Hollow CSIRO • State three reasons why Ptolemy’s model lasted for so long. buildToggle(‘a13’); Answer • It worked, ie it could be used to predict planetary positions to within 2°. • It was theologically acceptable as the Earth was near the centre of all motions. • It accounted for the observed planetary motions, retrograde motion and variations in brightness. • Describe one contribution of Islamic astronomers prior to Copernicus? buildToggle(‘a14’); Answer Islamic astronomers, apart from making their own observations, preserved and translated many of the original classical Greek manuscripts into Arabic, thus saving them from destruction so they were later available to Western European schol
