When a star moves off the main sequence and becomes a red giant it is brighter because
A) the star moves closer to Earth.
B) the size of the star increases.
C) the surface temperature increases.
D) the star's mass increases.

Question

Quizplus · Accepted Answer

As a star becomes a red giant, its outer layers expand significantly, increasing its size and luminosity, making it appear brighter.

When a Star Moves Off the Main Sequence and Becomes