20110314

Astronomy midterm question: waning crescent scenario

Astronomy 210 Midterm 1, spring semester 2011
Cuesta College, San Luis Obispo, CA

Shown at right is a scene from an animated TV show. Discuss a specific plausible time (or range of times) for this scene, assuming that it is not an eclipse, using a diagram showing the positions of the sun, moon, Earth, and an observer on Earth.

(Image credit: Matt Groening, Futurama, "Rebirth," Season 6, Episode 1, 20th Century Fox Television, 2010, 
http://www.gotfuturama.com/Multimedia/FrameGrabs/6ACV01/.)

Solution and grading rubric:
  • p = 20/20:
    Correct. Phase as shown is waning crescent, which is highest overhead at 9 AM (rises at 3 AM, and sets at 3 PM, so any time within that range would be plausible, may restrict times to between 3 AM to 6 PM as the sky is still dark, and moon is not yet fully upright/on the meridian). Correct diagram and reasoning.
  • r = 16/20:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t = 12/20:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram, phase, or time.
  • v = 8/20:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Problems with diagram, phase, and time.
  • x = 4/20:
    Implementation/application of ideas, but credit given for effort rather than merit. Explanation based on eclipses, solstices, etc.
  • y = 2/20:
    Irrelevant discussion/effectively blank.
  • z = 0/20:
    Blank.
Grading distribution:
Section 30676
Exam code: midterm01sl7k
p: 22 students
r: 4 students
t: 8 students
v: 13 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 4351):

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