Astronomy midterm question: moonset at sunrise?

Astronomy 210 Midterm 1, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board was asked and answered:

TheworldisRound...: When does the moon set?
Jon: When the sun rises.
--Adapted from http://answers.yahoo.com/question/index?qid=20101117173704AA9FK13

Discuss for which moon phase(s) this answer would be correct, or if this answer would never be correct for any moon phase, and how you know this. Support your answer using a diagram showing the positions of the sun, moon, Earth, and an observer on Earth.

Solution and grading rubric:

• p = 20/20:
  Correct. Moon setting at sunrise (6 AM) would have been highest overhead at 12 AM that same night, which would make it a full moon. 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.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 30674
Exam code: midterm01n0M3
p: 18 students
r: 3 students
t: 8 students
v: 9 students
x: 3 students
y: 0 students
z: 0 students

A sample "p" response (from student 0920):