Astronomy midterm question: evening star planet visible later?

Astronomy 210 Midterm 1, spring semester 2013
Cuesta College, San Luis Obispo, CA

A view of the horizon is shown below, as seen from San Luis Obispo, CA at a certain date/time. Carefully note the positions of the sun, and an unknown planet in the sky.


[Version 1]
Discuss why this this planet would not be visible at sunrise 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, this planet, Earth, and an observer on Earth.

[Version 2]
Discuss why this this planet would not be visible at midnight 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, this planet, Earth, and an observer on Earth.

Solution and grading rubric:

• p = 20/20:
  Correct. Correct and complete diagram, with observer at sunrise on Earth and a planet (either inside or outside of Earth's heliocentric orbit); shows and discusses how the planet just above west horizon at sunset (as an evening star) would not be visible anywhere in the sky at sunrise/midnight.
• 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. Problems with either diagram or discussion. At least understands that any planet near the sun in the sky cannot be seen at sunrise/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. May have planet orbiting Earth, but still discusses how planet visible at sunset could not be visible at sunrise/midnight.
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Misconceptions or non-relevant concepts.
• y = 2/20:
  Irrelevant discussion/effectively blank.
• z = 0/20:
  Blank.

Grading distribution:
[Version 1] Section 30674
Exam code: midterm01n4sT
p: 17 students
r: 1 student
t: 3 students
v: 9 students
x: 0 students
y: 0 students
z: 1 student

[Version 2] Section 30676
Exam code: midterm01sAb1
p: 33 students
r: 1 student
t: 3 students
v: 9 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1686), explaining how the planet would not be visible at sunrise:
A sample "p" response (from student 0317), using another type of diagram to explain how the planet would not be visible at sunrise:
A sample "p" response (from student 4336), explaining how the planet would not be visible at midnight:
A sample "t" response (from student 7580), identifying the planet as a morning star rather than an evening star (but still discussing how it would not be visible at midnight):
A sample "v" response (from student 1162), with some semblance of using the "snowboarder model" for identifying the local horizon for an observer: