Astronomy quiz question: absorption lines of a star

Astronomy 210 Quiz 5, spring semester 2014
Cuesta College, San Luis Obispo, CA

The absorption lines of a star are produced by:
(A) sunspots.
(B) parallax.
(C) electrons moving to lower energy levels.
(D) blackbody radiation passing through diffuse, cool gas atoms.

Correct answer (highlight to unhide): (D)

According to Kirchhoff's laws, the absorption lines of a star are the result of the cooler, diffuse outer layers surrounding the hotter and denser interior. The atoms in the outer layers have electrons that absorb certain photons (and re-emit them in different directions) from the continuous spectrum ("blackbody radiation") emitted by the star's interior. The result is that you start with the rainbow of a continuous spectrum, and then certain wavelengths are missing, producing the dark absorption lines of a star.

Section 30674
Exam code: quiz05n3Ne
(A) : 3 students
(B) : 1 student
(C) : 7 students
(D) : 14 students

Success level: 59% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.63

Section 30676
Exam code: quiz05suN7
(A) : 3 students
(B) : 3 students
(C) : 13 students
(D) : 20 students

Success level: 54% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.35