Question

Early astronomers were confused because the following planets sometimes reverse their direction:
(A) Mars
(B) Jupiter
(C) Saturn
(D) All of the above

Answer 1

Hint
We need to take into consideration that earlier astronomers had a completely different idea about our solar system. They considered Earth to be at the centre with the Sun and all the other planets revolving around it.

Complete step by step answer
This phenomenon where planets seem to suddenly reverse their direction is known as ‘retrograde motion’. In the early times astronomers were confused by this phenomenon because they considered earth to be at the centre of the universe with all the Sun and planets revolving around it. However in 1543 it was proven by Nicolaus Copernicus that it was actually the other way around, that Earth revolves around the Sun.
Usually all stars and planets appear to move from east to west in the night sky, however sometimes they appear to drift backwards. This is actually an illusion. The planets are not actually drifting backwards. Instead, our perception changes. This is because Earth completes its orbit in a much shorter period of time as compared to some of the other planets like Jupiter, Saturn or Mars.
The moment when Earth bypasses one of these planets it seems like the other planet has suddenly changed course and is now moving backwards. For example, it takes Earth to complete its revolution around the Sun in 365 Earth days. It takes Mars 687 Earth days to complete its revolution. So it’s apparent that at some point Earth overtakes Mars and moves past it. This is when we feel like Mars is moving backwards but in actuality, Earth just moved past Mars.
So, in conclusion all the three planets Jupiter, Saturn and Mars have a revolution period much greater than Earth. So all of the above undergo retrograde motion.
Therefore, the correct option is (D).

Note
The retrograde motion is not actually real and is just an illusion. And it is also observed with moons.