Astronomy midterm question: moon "waxing in the morning?"

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

The following claim was made on an online discussion board[*]:
Mk: When I teach Boy Scouts for the Astronomy merit badge, I tell them to remember, "It's always waning in the morning." So if you see the moon in the sky in the morning, when the sky is still dark, it must be a waning moon phase.
Discuss whether it is possible or not for an observer in San Luis Obispo, CA to also see a waxing moon phase in the sky in the morning, when the sky is still dark. Support your answer using a diagram showing the positions of the sun, moon, Earth, and an observer on Earth.


Solution and grading rubric:
  • p:
    Correct. Complete diagram and reasoning includes the following explanations:
    1. the waxing gibbous moon, which is highest overhead at 9 PM, sets at 3 AM;
    2. from 12 AM to 6 AM are morning hours when "the sky is still dark";
    3. so the waxing gibbous moon can be seen in a dark morning sky from 12 AM to 3 AM.
  • 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 70158
Exam code: midterm01s4uL
p: 20 students
r: 2 students
t: 13 students
v: 5 students
x: 3 students
y: 0 students
z: 0 students

A sample "p" response (from student 1313):

Another sample "p" response (from student 1805):

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