Astronomy midterm question: Zion National Park moon Instagram

Astronomy 210 Midterm 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

The image at right[*] posted on the Instagram account of the U.S. Department of the Interior depicts a moon low above a horizon during the day. Discuss whether or not this moon image is plausible, and how you know this. Support your answer using a diagram showing the positions of the sun, the moon, Earth, and an observer on Earth.

[*] instagram/p/mYnT4Ngu04/.

Solution and grading rubric:
  • p:
    Correct. The waning gibbous moon (more than the left half of the moon is lit up) is highest overhead at 3:00 AM, and would have risen six hours before at 9:00 PM, and set six hours later at 9:00 AM. In order for this picture to have been taken during the day, the time would need to sometime between after sunrise at 6:00 AM, and when the waning gibbous moon would set at 9:00 AM. Complete diagram and reasoning.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Diagram and/or explanation has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram or discussion.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Diagram and discussion problematic.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
Grading distribution:
Section 30676
Exam code: midterm01sh3P
p: 28 students
r: 8 student
t: 9 students
v: 3 students
x: 4 students
y: 0 students
z: 0 students

A sample "p" response (from student 3562):

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