Astronomy quiz question: mapping Milky Way spiral arms

Astronomy 210 Quiz 6, fall semester 2012
Cuesta College, San Luis Obispo, CA

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

Correct answer: (B)

Radio waves are relatively unaffected by interstellar gas and dust, and enable the locations of cold hydrogen gas clouds in most of the Milky Way to be mapped. Positions of massive main sequence stars can only give an indication of spiral arms immediately adjacent to the spur the sun is located in; and globular cluster positions are used to determine the location of the Milky Way.

Section 70158
Exam code: quiz06Sl4m
(A) : 9 students
(B) : 4 students
(C) : 13 students
(D) : 4 students

Success level: 19% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38