Astronomy quiz question: Milky Way shape

Astronomy 210 Quiz 6, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

How do we know that the Milky Way is shaped like a flat disk?
(A) Statistically, most other galaxies are shaped like flat disks.
(B) Distant stars appear to be dimmer than nearby stars.
(C) Naked-eye observations at dark sky locations.
(D) The precession of the axis of the Earth's rotation.

Section 70158
(A) : 10 students
(B) : 15 students
(C) : 23 students
(D) : 8 students

Correct answer: (C)

Since the stars of the Milky Way form a band across the night sky, as seen from Earth, its overall shape must be thin and flat, as opposed to spherical.

"Success level": 40% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.51

Section 70160
(A) : 7 students
(B) : 9 students
(C) : 11 students
(D) : 2 students

"Success level": 44% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43