Astronomy midterm question: Star Wars "That's no moon..." analysis

Astronomy 210 Midterm 2, fall semester 2015
Cuesta College, San Luis Obispo, CA

In the movie Star Wars (20th Century Fox, 1977), the Death Star was a giant spherical traveling space station that was initially mistaken as a "small moon." In the webcomic panel at right[*] it is further argued that the Death Star is "too small to be a moon." Discuss why the Death Star cannot be considered a moon, despite its small size. Explain using the International Astronomical Union classification scheme.

[*] Randall Munroe, "Small Moon," xkcd.com/1458/.

Solution and grading rubric:
  • p:
    Correct. Of the three IAU requirements (orbits the sun directly, has a rounded shape, cleared/dominates its orbit), if an object does not orbit the sun (or presumably any star) directly, but orbits a planet, then it is classified as a moon/satellite. Since the Death Star can travel through space, then it would not be a moon/satellite while it is not in orbit around a planet.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May argue that the Death Star is not a moon because it does not orbit the sun (when the IAU classification scheme asks whether the object directly orbits the sun, or is in orbit around another object such as a planet), but understands the importance of the first classification question.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. May also involve the shape of the Death Star and/or its ability to gravitationally dominate other objects as important, other than its orbiting another object in orbit around the sun (or any star).
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion only tangentially related to the IAU classification scheme.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the IAU classification scheme.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
Grading distribution:
Section 70160
Exam code: midterm02n1N0
p: 16 students
r: 9 students
t: 5 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 7063), also sharing tangentially personal opinions on Star Wars:

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