Astronomy quiz question: Milky Way spiral arm evidence

Astronomy 210 Quiz 6, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

__________ is/are evidence that spiral arms extend across the Milky Way disk.
(A) Globular cluster positions.
(B) Positions of massive main sequence stars.
(C) The Doppler effect.
(D) Radio waves from cold hydrogen gas clouds.

Correct answer: (D)

While the luminous stars in response (B) is used to map out an indication of spiral arms and spurs in our immediate vicinity of the Milky Way, response (D) refers to the radio waves from cold hydrogen gas clouds that are relatively unobstructed by the interstellar gas and dust, and this data allows essentially the entire spiral arm structure of the Milky Way to be mapped. Response (A) refers to how the location of the center of the Milky Way is determined.

Section 30674
Exam code: quiz06n4Ke
(A) : 19 students
(B) : 8 students
(C) : 3 students
(D) : 7 students

"Success level": 22% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.30