Instructor, when you complete or partially complete this exercise. in the earth-centered view of the universe, the motion of the planets was explained by use of the (a) in this type of motion, as a planet orbits the earth (since the universe was thought to be earth centered) in a large circle, the planet also orbits a smaller circle centered on the larger circle. this idea was a useful predictor of the motion of the planets for more than (b) years.