20110313

Astronomy midterm question: late-night Venus, Jupiter?

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:
mickafeld: ...How do you [tell] the difference between Venus and Jupiter?
duke_of_uris: If you see a very bright planet late at night, it's Jupiter [and not Venus]...
-- http://au.answers.yahoo.com/question/index?qid=20100507202644AANiYYU
Discuss if this answer is correct or incorrect, and how you know this. Support your answer using a diagram showing the positions of the sun, Venus, Jupiter, Earth, and an observer on Earth.

Solution and grading rubric:
  • p = 20/20:
    Correct. Correct and complete diagram, with Venus (inner heliocentric orbit) and Jupiter (outer heliocentric orbit); Jupiter can be seen late at night if it is near opposition to Earth, but Venus cannot in any part of its orbit.
  • 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. Typically has diagram of heliocentric orbits of Venus, Earth, and Jupiter, but discussion is problematic.
  • v = 8/20:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Diagram is problematic (Venus and Jupiter both in inner heliocentric orbits, or both in outer heliocentric orbits), but at least discussion is consistent with incorrect diagram.
  • x = 4/20:
    Implementation/application of ideas, but credit given for effort rather than merit. Problematic diagram (geocentric orbits, no orbits etc.), problematic discussion.
  • y = 2/20:
    Irrelevant discussion/effectively blank.
  • z = 0/20:
    Blank.
Grading distribution:
Section 30676
Exam code: midterm01sl7k
p: 18 students
r: 7 students
t: 5 students
v: 6 students
x: 12 students
y: 1 student
z: 0 students

A sample "p" response (from student 1103):

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