Astronomy midterm question: conjunction of waxing crescent moon and Venus

Astronomy 210 Midterm 1, spring semester 2014
Cuesta College, San Luis Obispo, CA

Shown above is a purported time-lapse photograph[*] of the moon and Venus setting (near a statue). Discuss how this is a plausibly real (and not a fake) photograph. Support your answer using a diagram showing the positions of the sun, Venus, moon, Earth, and an observer on Earth.

[*] Josselin Desmars, "Moon and Venus conjunction over Corcovado, September 8, 2013 (Rio de Janeiro, Brazil)," 

Solution and grading rubric:
  • p:
    Correct. Correct and complete diagram (with the sun, moon, Venus, and observer on Earth), and discusses (1) moon must be waxing crescent setting after sunset, and (2) Venus must be setting as an evening star.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Diagram and/or explanation has minor errors. May instead have waning crescent moon and morning star Venus (which would have them rising just before sunrise).
  • t: Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram or discussion. At least has correct waxing crescent on diagram, or correct evening star Venus on diagram.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Diagram and discussion problematic.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Misconceptions or non-relevant concepts.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
Grading distribution:
Section 30674
Exam code: midterm01n3vE
p: 4 students
r: 13 students
t: 4 students
v: 8 students
x: 0 students
y: 0 students
z: 0 students

Section 30676
Exam code: midterm01SuN7
p: 9 students
r: 14 students
t: 14 students
v: 7 students
x: 0 students
y: 1 student
z: 0 students

A sample "p" response (from student 6536):

A sample "r" response (from student 0123):

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