Astronomy midterm question: Mars and Venus low in the west at sunrise?

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

An astronomy question on an online discussion board was asked and answered[*]:

Q: Well, I observed a bright red dot that is Mars low in the west at sunrise. At the same time there was another bright white dot right next to Mars. What is it?
A: I think it's Venus.

Discuss how this answer is implausible 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=20140311092430AAKTg2Q.

Solution and grading rubric:

• p:
  Complete diagram and reasoning includes the following explanations for an observer on Earth at or around sunrise (6 AM):
  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 west horizon; and
  2. Venus, when placed anywhere in an orbit around the sun inside of Earth's orbit, can only be seen low over the east horizon at sunrise.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Has east/west horizons switched, such that Mars and/or Venus are setting at or around sunset.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram or discussion. May have both Venus and Mars in an inner (or outer) orbit with east/west horizons switched, such that Venus and Mars are rising at or around sunrise (or sunset).
• 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 70160
Exam code: midterm01nDm3
p: 14 students
r: 10 students
t: 9 students
v: 0 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1352):
Another sample "p" response (from student 8954):