Astronomy quiz question: first "evening star" to set

Astronomy 210 Quiz 2, spring semester 2015
Cuesta College, San Luis Obispo, CA

A view of the San Luis Obispo, CA sky is shown below for September 9, 2015 with the planets Saturn and Mercury.


Within the next 24 hours, __________ will set first.
(A) Saturn.
(B) Mercury.
(C) (There will be a tie.)
(D) (Neither of these planets will set.)

Correct answer (highlight to unhide): (B)

Over the course of the day, Earth's rotation will cause objects on the celestial sphere to move from east to west, so Mercury will set just after the sun sets, later followed by Saturn just before midnight.

Section 30674
Exam code: quiz02n4S7
(A) : 8 students
(B) : 27 students
(C) : 1 student
(D) : 4 students

Success level: 69% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75