Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q11.2
[15 points.] Consider the following observation:
"The central reason astronomers have been slow to understand the Milky Way is simply because we are deep in the thick of things: The other stars, the gas and especially all the dust in the disk prevent us from seeing the full extent of the galaxy's structure."Explain how it is still possible to map the spiral arm structure of the Milky Way.
--Henry Freudenreich, Am. Sci. vol 87 no. 5, p. 418 (1999)
Solution and grading rubric:
- p = 15/15:
Correct. O- and B-type stars, due to their extremely short lifetimes, are born and die only in the spiral arms; and are bright enough to be seen through some of the obscuring gas and dust. Similarly for HII (emission) nebulae. 21 cm wavelength radio waves emitted from cold hydrogen gas are not obscured by gas and dust. Observing the locations of all three result in a spiral arm map of the Milky Way. - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Discusses locating nearby stars without being very specific about the type of stars (typically O- and B-type). - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Describes direct or indirect evidence for the thin disk structure of the Milky Way, but not the spiral arm structure. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 1073
p: 14 students
r: 3 students
t: 6 students
v: 6 students
x: 1 student
y: 0 students
z: 1 student
A sample of a "p" response (from student 1000) is shown below:
Another "p" response (from student 8556), with an illustration of density wave star formation: 
No comments:
Post a Comment