Astronomy quiz question: red supergiant vs. red giant

Astronomy 210 Quiz 4, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

[4.0 points.] A red supergiant is known to be larger in size than a red giant because it is:
(A) same temperature as, but more luminous than a red giant.
(B) same temperature as, but less luminous than a red giant.
(C) same luminosity as, but hotter than a red giant.
(D) same luminosity as, but cooler than a red giant.

Section 70160
(A) : 29 students
(B) : 0 students
(C) : 1 student
(D) : 1 student

Correct answer: (A)

From Wien's law, the supergiant and the giant must be the same temperature, because they have the same color. From the Stefan-Boltzmann law, for two stars of the same temperature, the more luminous star must be larger in size.

"Difficulty level": 93%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.25