Astronomy midterm question: low waning crescent moon in twilight sky

Astronomy 210 Midterm 1, spring semester 2016
Cuesta College, San Luis Obispo, CA

Shown at right is a photograph[*] published with the following caption:
The Golden Gate Bridge framed the [low] crescent shaped moon perfectly as viewed [facing south] from the Marin headlands of Sausalito.
Assuming that this is a twilight sky (dark, but not completely dark) in this photograph, discuss why this caption is plausibly correct. Support your answer using a diagram showing the positions of the sun, moon, Earth, and an observer on Earth.

[*] Frederic Larson (April 5, 2005) for The Chronicle, in Katie Dowd, "83 Years Ago Today, Construction Started on the Golden Gate Bridge," January 5, 2016, 

Solution and grading rubric:
  • p:
    Correct. Complete diagram and reasoning includes the following explanations:
    1. identifies the waning crescent moon, which rises at 3 AM, is highest overhead at 9 AM, and sets at 3 PM;
    2. sky is "dark, but not completely dark," so the photograph must have been taken just before sunrise (approximately 5-6 AM);
    3. this range of "twilight" times is consistent with the moon being "low," (still rising and not yet highest overhead), but before the sunrise.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors.
  • 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:
Grading distribution:
Section 30674
Exam code: midterm01n0rD
p: 8 students
r: 3 students
t: 4 students
v: 4 students
x: 3 students
y: 0 students
z: 0 students

Section 30676
Exam code: midterm01sN0w
p: 23 students
r: 8 students
t: 5 students
v: 10 students
x: 8 students
y: 0 students
z: 0 students

A sample "p" response (from student 8211):

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