According to Copernicus, the retrograde motion for Mars must occur:
A)at inferior conjunction, when Mars laps the Earth and passes between us and the Sun.
B)at superior conjunction, when Mars lies on the far side of the Sun.
C)at quadrature, when Mars lies exactly 90 degrees east or west of the Sun.
D)at greatest elongation, when Mars can get up to 47 degrees from the Sun.
E)at opposition, when the Earth overtakes Mars and passes between Mars and the Sun.

Question

Quizplus · Accepted Answer

Retrograde motion occurs when a planet appears to move backward in its orbit as viewed from Earth. This occurs when Earth passes between the planet and the Sun, which happens at opposition. Therefore, the retrograde motion for Mars must occur at opposition, making choice E the correct answer. Retrograde motion occurs when a planet appears to move backwards in the sky relative to the fixed stars. This occurs when Earth overtakes and passes by the slower-moving outer planets, such as Mars, in their orbits around the Sun. This happens at what is called opposition, when Mars is directly opposite the Sun in the sky as seen from Earth. Therefore, option E is the correct answer.

According to Copernicus, the Retrograde Motion for Mars Must Occur