20120311

Astronomy midterm question: moon phase for night sailing?

Astronomy 210 Midterm 1, spring semester 2012
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:
donc:You are planning to do some evening ocean sailing some time in the near future. Because of scheduling conflicts, the only time that you can sail is 9:00 PM. Since you would like to have the moon in the sky to help you navigate, what phases could the moon be?
DH: [F]irst quarter...
Discuss whether or not this answer is correct, and how you know this. Support your answer using a diagram showing the positions of the sun, moon, Earth, and an observer on Earth.

*Source: http://answers.yahoo.com/question/index;_ylt=AuNNpNJs5Vf9Sxu5fcsJVrcjzKIX;_ylv=3?qid=20101105162240AArByFS.

Solution and grading rubric:
  • p = 20/20:
    Correct. The first quarter moon is highest overhead for an observer at 6:00 PM on Earth, setting six hours later at midnight, so would still be above the horizon at 9:00 PM. Correct diagram and reasoning.
  • r = 16/20:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discusses how diameter affects either light-gathering power or resolving power, other diameter/power discussion incomplete.
  • t = 12/20:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram or discussion.
  • v = 8/20:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Substantive discussion, but missing/problematic diagram.
  • x = 4/20:
    Implementation/application of ideas, but credit given for effort rather than merit. Problematic discussion, diagrams with the moon orbiting the sun, etc.
  • y = 2/20:
    Irrelevant discussion/effectively blank.
  • z = 0/20:
    Blank.
Grading distribution:
Section 30674
Exam code: midterm01neE7
p: 14 students
r: 6 students
t: 3 students
v: 4 students
x: 6 students
y: 0 students
z: 0 students

A sample "p" response (from student 0401):
Another sample "p" response (from student 0010):

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