DEPARTMENT OF ASTRONOMY

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ASTRONOMY 301
Introduction to Astronomy
Fall 2002


Dr. Bash - Second Exam - Common Mistakes


Exam #2


Please write your name on each page, be brief and concise, answer in the space provided, and, if necessary, continue your answer on the back of the sheet on which the question is printed.

1. Why do stars spend the majority of their lives on the main sequence?
  • Stars DO NOT move up the main sequence.
  • They are stable and balanced when they burn any fuel (not just H).
  • The question does not ask you to compare low mass to high mass stars.


2. What kind of galaxies will live the longest and why?
The star formation process makes stars of all masses, including small masses. So the key is to keep forming new stars.

3. What is the physical cause of the mass-luminosity relation for main sequence stars?
  • Many students did not mention hydrostatic equilibrium.
  • Answer not E=mc2.
  • Give physical reason, not just state L α M3.5.
  • More mass means more fuel available but doesn't explain increased fusion rate. Need PαρT.

4. Why does the presence of O stars in a galaxy suggest that the region containing the O stars is a star forming region?
Does not have to do with Pop I vs. Pop II stars.

5. What causes a star to die?
Many students do not consider the second point. The star can't get a high enough temperature to ignite the subsequent reaction, so it dies.

6. Why would we expect the current expansion of the Universe to slow down?
Lots of students explained the problem using the Hubble Law instead of gravity.



 
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10 December 2002
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