Question

when does mars undergo retrograde motion (as seen from earth)?

Explanation:

Mars undergoes retrograde motion as seen from Earth when Earth overtakes Mars in their orbits around the Sun, typically around opposition (when Mars is opposite the Sun from Earth). This is due to Earth's faster orbital speed.

Answer:

Mars undergoes retrograde motion (as seen from Earth) when Earth overtakes Mars in their orbits around the Sun, typically around opposition.