Astronomy quiz question: last zodiac constellation to set

Astronomy 210 Quiz 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

The diagram at right shows the positions on April 25 of the zodiac constellations Sagittarius, Scorpius, and Libra for an observer in San Luis Obispo, CA. Ignore daylight saving time. Assume you can see stars in daylight. Within the next 24 hours, __________ will be the last zodiac constellation to completely set below the horizon.
(A) Sagittarius.
(B) Scorpius.
(C) Libra.
(D) (There is a tie.)
(E) (None of these zodiac constellations will completely set below the horizon.)

Correct answer (highlight to unhide): (A)

Using a starwheel to advance the time hourly from 1:00 AM on April 25, Libra will completely set below the horizon at approximately the same as Scorpius, then Sagittarius will be the last to completely set approximately 10-11 hours later.

Section 30674
Exam code: quiz01nW0r
(A) : 23 students
(B) : 1 student
(C) : 7 students
(D) : 3 students
(E) : 8 students
(No response: 1 student)

Success level: 56% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.29

Section 30676
Exam code: quiz01Su8L
(A) : 24 students
(B) : 7 students
(C) : 11 students
(D) : 6 students
(E) : 7 students

Success level: 46% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.53