[4.0 points.] How does Copernicus' model explain the retrograde motion of a planet?
A. The only perfect shape is a circle, and the only perfect motion is uniform motion.
B. A planet slows down in its orbit when it is further from the sun, and speeds up in its orbit when it is closer to the sun.
C. A planet moves around a circle that itself moves along an orbit around the Earth.
D. A planet has a different orbital distance and speed around the sun from the Earth's orbital distance and speed around the sun.
Answer:D
[4.0 points.] How does Copernicus' model explain the retrograde motion of a planet?
A. The only perfect shape is a circle, and the only perfect motion is uniform motion. B. A planet slows down in its orbit when it is further from the sun, and speeds up in its orbit when it is closer to the sun. C. A planet moves around a circle that itself moves along an orbit around the Earth. D. A planet has a different orbital distance and speed around the sun from the Earth's orbital distance and speed around the sun.