Imagine a planetary system with a star and a single Earth-mass planet. Astronomers determine that the planet follows an elliptical orbit. What orbit does the star follow?
A) It remains motionless, because it is so much more massive than the planet.
B) It follows an elliptical orbit with the center of mass of the system at one focus.
C) It remains motionless, because it is so far from the planet.
D) It follows an elliptical orbit with the planet at one focus.

Question

Quizplus · Accepted Answer

In a two-body system, both bodies orbit their common center of mass. Even though the star is much more massive and its orbit smaller, it still follows an elliptical path around this point, not remaining motionless.

Imagine a Planetary System with a Star and a Single