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 rising just after midnight. At the same time there was another bright white dot right next to Mars. What is it?Discuss how this answer is plausible 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, Saturn, Earth, and an observer on Earth.
A: I think it's Saturn.
Solution and grading rubric:
Complete diagram and reasoning includes the following explanations for an observer on Earth at or around midnight (12 AM):
- 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
- Saturn is also placed in an orbit around the sun outside of Earth's orbit such that it is visible low over the observer's east horizon.
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 Saturn are setting at or around midnight.
Problems with either diagram or discussion. Problems with either diagram or discussion. May have:
- observer placed at midnight, but has Mars and Saturn both high overhead; or
- observer not placed at midnight and east/west horizons switched.
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Diagram and discussion problematic.
Implementation/application of ideas, but credit given for effort rather than merit.
Irrelevant discussion/effectively blank.
Exam code: midterm01Sn0w
p: 16 students
r: 9 students
t: 16 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students
A sample "p" response (from student 1027):
Another sample "p" response (from student 2622):
A sample "r" response (from student 4472), with Mars and Saturn setting at midnight: