Astronomy midterm question: Venus as evening star?

Astronomy 210 Midterm 1, fall semester 2011
Cuesta College, San Luis Obispo, CA

[20 points.] Consider an online definition(*) of evening star:
evening star
1. a bright planet seen in the western sky at or soon after sunset, especially Venus.
Discuss whether or not using Venus as an example is consistent with this definition. Support your answer using a diagram showing the positions of the sun, Venus, and an observer on Earth.

*Source: http://dictionary.reference.com/browse/evening+star.

Solution and grading rubric:
  • p = 20/20:
    Correct. Correct and complete diagram, with Earth (outer heliocentric orbit) and Venus (inner heliocentric orbit); shows and discusses how Venus can be seen above the west horizon at sunset.
  • r = 16/20:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Diagram and/or explanation has minor errors.
  • t = 12/20:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Heliocentric diagram but instead discusses how Venus cannot be seen at night (or more specifically, at midnight).
  • v = 8/20:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Diagram and discussion problematic (e.g. Venus in outer heliocentric orbit, or shows geocentric solar system).
  • x = 4/20:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y = 2/20:
    Irrelevant discussion/effectively blank.
  • z = 0/20:
Grading distribution:
Section 70158
Exam code: midterm01nH3d
p: 10 students
r: 4 students
t: 7 students
v: 7 students
x: 0 students
y: 2 students
z: 0 students

A sample "p" response (from student 7272):

Another sample "p" response (from student 2286):

An honest "y" response (from student 1177):

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