Retrograde motion of the outer (superior) planets occurs because: a. planets atually back up in their orbits occasionally b. the earth is moving in its orbit faster than any superior planet, so when the planet is at opposition (opposite the sun in the sky), the planet seems to go backwards the earth is moving in its orbit faster than any superior planct, so when the planet is in conjunction (near the sun in the sky, the planet seems to go backwards c. d. the outer planets move quickly, so earth seems to go backwards