Question

Retrograde motion of a superior planet occurs when Earth catches up to and passes the superior planet. Suppose a superior planet completes its orbit in exactly 18 months (sidereal period). Then ____ months will elapse between a time when Earth passes this planet and the next time it does so.

Answer 1

Answer:

36

Explanation:

Earth's orbit is shorter than all the other superior planets. Superior planets are those planets that are further from the sun than Earth.

Retrograde motion of a planet is the motion opposite to other planetary bodies within its system.

Retrograde motion is apparent. It is not real in the sense that the superior planet does not literally move backwards in its orbit.

So if the time taken for a superior planet to complete its orbit is 18 months, once Earth passes this planet, retrograde motion of the planet start. It would take Earth twice that time in order to catch up with that same planet and pass it again.

Like I said earlier, it is possible because Earth's orbit is shorter.