20140316

Astronomy midterm question: SOFIA vs. James Webb Space Telescope

Astronomy 210 Midterm 1, spring semester 2014
Cuesta College, San Luis Obispo, CA

The primary mirror diameters and locations of two different near infrared telescopes are shown at right. Discuss which telescope will produce better images, and specifically explain why. Support your answer using the properties of telescopes, telescope powers, and the effects of Earth's atmosphere.

Solution and grading rubric:
  • p:
    Correct. Discusses at least one each of the following effects of telescope parameters, and location: (1) how diameter of primary mirror determines both light-gathering power and resolving power, such that a larger diameter mirror of the James Webb Space Telescope would result in making fainter objects brighter, and allowing finer details to be seen; and (2) how the opacity and turbulence of the atmosphere blocks near infrared light (affecting light-gathering power), and distorts images (affecting resolving power), such that the James Webb Space Telescope would be affected less by opacity and turbulence.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of the two points (1)-(2) correct, other is problematic/incomplete.
  • t: Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram or discussion. Both points (1)-(2) problematic/incomplete, or one point correct while other is missing.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion of telescope parameters and atmosphere effects is garbled.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion not related to telescope parameters or atmosphere effects.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: midterm01n3vE
p: 14 students
r: 3 students
t: 8 students
v: 3 students
x: 0 students
y: 0 students
z: 1 student

Section 30676
Exam code: midterm01SuN7
p: 28 students
r: 1 student
t: 13 students
v: 3 students
x: 0 students
y: 0 students
z: 2 students

A sample "p" response (from student 1357) discussing light-gathering power, resolving power, and seeing conditions:

Another sample "p" response (from student 3158) also discussing light-gathering power and resolving power, but instead refers to lack of atmosphere opacity:

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