## 20171012

### Astronomy midterm question: plausible waning gibbous moon photomontage?

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

Shown at right[*] is a photographic montage of a moon, starlight sky, and a model. Discuss whether this composition is plausible or implausible for an observer in San Luis Obispo, CA, given the phase and position of the moon in the sky, and the presence of stars in the sky. (Ignore the effect of natural/artificial light sources that illuminate this picture.) Support your answer using a diagram showing the positions of the sun, moon, Earth, and an observer on Earth.

[*] @amandawalker247, instagram.com/p/BUTABCll9rl/.

Solution and grading rubric:
• p:
Complete diagram and reasoning includes the following explanations:
1. identifies the phase as a waning gibbous moon;
2. which is highest overhead at 3 AM, rises six hours earlier at 9 PM, and sets six hours after being highest overhead at 9 AM;
3. the presence of stars indicates the sun is not up, so possible night times range from 6 PM to 6 AM;
and thus concludes that the composition is plausible for 3 AM (or any time between 9 PM and 6 PM). May have included discussion on effect of moon's or San Luis Obispo's light pollution on stars, apparent lighter lower part of the sky coming from the sun, etc.
• r:
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:
Contains right ideas, but discussion is unclear/incomplete or contains major errors.
• v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to draw a moon phase diagram and apply rise/overhead/set times.
• x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion not clearly based on a moon phase diagram.
• y:
Irrelevant discussion/effectively blank.
• z:
Blank.
Grading distribution:
Section 70160
Exam code: midterm01nDm3
p: 21 students
r: 3 students
t: 4 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 3432):