20160114

Astronomy final exam question: comparing temperatures of Pollux versus Bellatrix

Astronomy 210 Final Exam, fall semester 2015
Cuesta College, San Luis Obispo, CA

Pollux is a star that is less luminous, but is larger in size than Bellatrix. Determine which star has a hotter surface temperature (or if there is a tie), and discuss how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

Solution and grading rubric:
  • p:
    Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to demonstrate how Pollux (larger in size) must be much cooler in temperature in order to be less luminous (or vice versa, where Bellatrix (smaller in size) must be much hotter in temperature in order to be more luminous).
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion not clearly based on Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Section 70158
Exam code: finalS157
p: 22 students
r: 0 students
t: 14 student
v: 0 students
x: 1 student
y: 0 students
z: 1 student

Section 70160
Exam code: finalN157
p: 12 students
r: 0 students
t: 6 student
v: 3 students
x: 1 student
y: 1 student
z: 2 students

A sample "p" response (from student 1822):

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