Question

Which planet shows retrograde motion?
(A) Venus
(B) Mercury
(C) Jupiter
(D) Mars

Answer 1

Hint
Retrograde motion refers to backward motion of an object. If a planet exhibits this motion it would imply that the planet appears to move backwards from its original path for some interval of time.

Complete step by step answer
Many great civilisations and scientists have been interested in the study of astronomical objects and their behaviour. The earliest attempts made by humans in this endeavour where to find a model for our universe.
In this list, first came the geocentric model that proposed that the Earth was at the centre of the cosmos, and other stars and planets revolved around it in perfect circles. But as the instruments to observe the sky got better, this model evolved to the heliocentric model with the Sun at the centre and other planets orbiting it in circular motions. This model seemed to solve many astronomical problems at the time, but soon an inexplicable phenomenon was observed.
This was the retrograde motion of Mars. Mars seemed to move west to east against the fixed background of stars but then would mysteriously reverse direction for a short period of time before returning to the original path again. This problem was solved when Copernicus proposed an order of the planets.
Hence, from the above information we can see that the correct answer is option D: Mars.

Note
The retrograde motion occurs because the farther the planet is from the Sun, the slower it revolves around it. So, as Mars is farther than the Earth, at one point the slow-moving Mars is overtaken by the fast-moving Earth. So, the eastward motion of Mars seems to reverse direction for a small period of time.