Astronomy midterm question: crescent moon lower than the sun?

Astronomy 210 Midterm 1, fall semester 2018
Cuesta College, San Luis Obispo, CA

Shown at right is a photographic montage[*] of a crescent moon just above a mountain range, with the sun higher above the mountains, off to the left of the photograph. Discuss whether this composition is plausible or implausible for an observer in San Luis Obispo, CA, given the phase and position of the moon in the sky, and the time of day. Support your answer using a diagram showing the positions of the sun, moon, Earth, and an observer on Earth.

[*] instagram.com/p/BhZUQTFFHLw/.

Solution and grading rubric:

• p:
  Complete diagram and reasoning, includes the following explanations:
  1. identifies the moon as a waning crescent, due to the left side of the moon being illuminated;
  2. identifies this moon as rising or setting ("just above a mountain range");
  3. since the waning crescent is highest overhead at 9 AM, then it rises at 3 AM (six hours earlier than 9 AM), which is before sunrise; and sets at 3 PM at (six hours later than 9 PM);
  4. since the sun is "a little higher [than the moon] above the mountains," this must be either a few hours after sunrise, or a few hours before sunset;
  and thus argues that the scene is implausible (as the sun cannot be above the horizon while waning crescent moon rises at 3 AM), or plausible (as the sun could be above the horizon while the waning crescent moon sets at 3 PM, although the horns of the moon would be pointing in the wrong direction, which would actually be another argument for implausibility.)
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. At least discusses (1)-(3), recognizing waning crescent moon as either rising or setting.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Primarily discusses waning crescent moon being overhead.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to draw a moon phase diagram and apply rise/overhead/set times.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion not clearly based on a moon phase diagram.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm01Sa1Y
p: 12 students
r: 9 students
t: 7 students
v: 8 students
x: 1 student
y: 0 students
z: 0 students

Section 70160
Exam code: midterm01n4mR
p: 1 student
r: 7 students
t: 7 students
v: 3 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 0423)
A sample "p" response (from student 7175)