Retrograde Motion

Question 1

What is the phenomenon when planets appear to move backward in the sky?

Answer 1

Retrograde motion

This is an apparent motion observed from Earth.

Question 2

What causes retrograde motion of planets?

Answer 2

Relative positions and motions of Earth and other planets

This occurs when Earth overtakes an outer planet.

Question 3

What happens to a planet’s apparent motion during retrograde?

Answer 3

The planet appears to move westward (backward) temporarily against the background of stars

This is a temporary effect until the overtaking is complete.

Question 4

What occurs after Earth overtakes an outer planet?

Answer 4

The planet resumes its normal eastward motion

This marks the end of the retrograde appearance.

Question 5

Give an example of retrograde motion.

Answer 5

When Earth goes faster than Mars, Mars looks like it’s going backward in the sky for a short time

This is similar to observing a slower car appearing to move backward while being overtaken.

Question 6

Fill in the blank: Retrograde motion occurs when a planet appears to move _______.

Answer 6

backward

Question 7

True or False: Retrograde motion is a permanent motion of planets.

Answer 7

False

Retrograde motion is a temporary appearance.

Question 8

What analogy is used to describe retrograde motion?

Answer 8

Being in a car driving faster than another car next to you

As you pass the slower car, it appears to move backward.