20170311

Astronomy midterm question: Mars in the east and Venus in the west at sunset?

Astronomy 210 Midterm 1, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board was asked and answered[*]:
g12: How can I find Mars and Venus?
Chr: Right now [February 2012] Mars is low in the east at sunset, while at the same time 
 that Venus is low in the west.
Discuss how this answer could be correct for an observer in San Luis Obispo, CA, and how you know this. Support your answer using a diagram showing the positions of the sun, Mars, Venus, Earth, and an observer on Earth.

[*] answers.yahoo.com/question/index?qid=20120205171726AAsMiO0.

Solution and grading rubric:
  • p:
    Complete diagram and reasoning includes the following explanations for an observer on Earth at sunset (6 PM):
    1. Mars can be placed in an orbit around the sun outside of Earth's orbit such that it is visible low over the observer's east horizon; and
    2. Venus can be placed in an orbit around the sun inside of Earth's orbit such that it is visible low over the observer's west horizon.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Problems with either diagram or discussion. May have:
    1. Mars in an inner orbit and/or Venus in an outer orbit; or
    2. observer not placed at sunset and/or east/west horizons switched.
  • 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.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30676
Exam code: midterm01sP4m
p: 25 students
r: 3 students
t: 14 students
v: 1 student
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 0247):

Another sample "p" response (from student 2412):

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