## 20120503

### Astronomy midterm question: comparing different temperature, same size stars

Astronomy 210 Midterm 2, spring semester 2012
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:
lilred309012004: What can we expect...when we look at stars [the same distance from Earth] with different surface temperatures but the same size?
abhi: [T]he star will be much brighter if it is...hot [and] blue...and much fainter and redder if it is...cool...
Decide whether or not if this answer is correct, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

• p = 20/20:
Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to show that a hotter, bluer star will be more luminous than a cooler, redder star.
• r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors.
• v = 8/20:
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-Boltzman law.
• x = 4/20:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzman law.
• y = 2/20:
Irrelevant discussion/effectively blank.
• z = 0/20:
Blank.
Section 30676
Exam code: midterm02sA4r
p: 24 students
r: 6 students
t: 6 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 0308):
Another sample "p" response (from student 4444):
A sample "v" response (from student 5476), misapplying Wien's law:
Yet another sample "v" response (from student 1033), misapplying the Stefan-Boltzmann law: