A planet's sidereal year is different from its synodic year because the
A) Earth moves.
B) planet's speed changes along its elliptical orbit.
C) planet rotates about its own axis in addition to its orbital motion.
D) the planet moves.

Question

Quizplus · Accepted Answer

The sidereal year is the time it takes for a planet to orbit the Sun once with respect to the fixed stars, while the synodic year is the time it takes for a planet to return to the same position with respect to the Sun and Earth. The difference arises because Earth itself is moving around the Sun as the other planet completes its orbit.

A Planet's Sidereal Year Is Different from Its Synodic Year