A101U Final Examination -- Spring 1994

Instructions:  This exam consists of 14 short answer 
questions.  Answer 11 of the 14 short questions on the 
exam or the paper I will provide you.  If you answer 
more than 11 of the 14 short questions, mark the 3 you 
DON'T want me to grade (with a big "x" or 
something...just be unambiguous).  If you have more 
than 11 questions answered and have left me no marks, I 
will grade the first 11.  

The questions are worth 9 points each.  I expect 
answers of 3-5 sentences or 2-3 sentences with an 
accompanying diagram.  You should have enough space to 
write in your answers on the exam, but if you need more 
paper or just some scratch paper, please raise your 
hand.  Writing in complete sentences is not required, 
but it may be helpful to express your point.  You don't 
need to repeat the question as part of your answer.

You should find that 2 hours will be ample time to 
finish this exam.  If you finish early, please leave 
quietly so as not to disturb others.  I encourage you 
to read back over your exam when you are finished to 
make sure you answered the correct number of questions 
completely.  I will periodically let you know how much 
time is left, so it should be easy for you to pace 
yourself to finish the exam in plenty of time.  You 
have the full 2 hours and 20 minutes should you need 
this much time.  That's enough for 12 minutes per 
question (out of 11 questions).

After you have completed the exam, you may come up 
to the front of the room and claim any graded papers 
(such as skylabs) you have not yet received from me.  
All unclaimed papers as well as the graded final (with 
a key posted) will be left in front of my office in a 
box through June.  The final exam will be graded 
Tuesday/Wednesday with exam and course grades posted on 
the wall outside my office (Johnson 216) by Thursday 
afternoon, if not before.  I will be around most of the 
day Thursday after 3 pm (and Friday/Saturday after 3) 
to answer questions about your grades and your final 
exam.  I'm leaving for vacation Tuesday, June 14-19, 
but I will be more than happy to discuss the course and 
your grade with you at times besides that.

When everyone has a copy of the final, you may 
turn the cover page over and begin.  Note that each 
page has questions on both sides.

(1)  In the galaxy data table for homework #4, we found that 
     there were very few extremely faint galaxies in the 
     table (very few 14th magnitude galaxies relative to the 
     numerous 11th magnitude galaxies).  

	(a)  (1 points)  Would you classify this problem as a 
	     random or systematic error?
	(b)  (3 points)  Explain by stating how this fits with 
	     the definition for the type of error you chose. 
	(c)  (5 points)  Without observing any more galaxies, 
	     how could you eliminate this error in your sample?  
	     It is possible, and there are many ways!  

(2)  Mercury and Mars both have very similar masses, but 
     Mars has a slight atmosphere of Carbon Dioxide (CO2) 
     while Mercury has no atmosphere.

	(a)  (6 points)  Why does Mars have CO2 in its 
	     atmosphere but not some of the other gases that 
	     were once common among the inner planets, like 
	     water vapor (H2O), Hydrogen and Helium?
	(b)  (3 points)  Why does Mercury lack even the small 
	     amount of CO2 that Mars has managed to hold on to?

(3)  A common misconception about the seasons is that the 
     temperature changes are caused merely by the proximity 
     of the Earth to the Sun at certain times of the year 
     (so, summer occurs when Earth is closer to the Sun).  
     State one basic observation that anyone could easily 
     make that would contradict this notion, and explain the 
     contradiction.

(4)  Lines in stellar spectra can be affected by a variety 
     of factors.  For each of the three situations given 
     below, describe how you would expect the spectral line 
     to change from the typical situation that you would 
     expect in a stationary, "standard" star.  State whether 
     the line shifts to the red or blue (or not at all) and 
     state whether the line is broadened or narrowed (or 
     remains the same width).  You may sketch the original 
     and modified lines as your answer, but be sure to label 
     which way is red and which is blue.  Treat each as an 
     independent case.

	(a)  (3 points)  The star is moving toward us at a high 
	     velocity (but nowhere close to the speed of 
	     light).
	(b)  (3 points)  The star is now a giant star, much 
	     larger than the original star but with the same 
	     temperature.
	(c)  (3 points)  The star is rapidly rotating, with the 
	     pole of the rotation facing directly toward us.

(5)  If we were to suddenly increase the Temperature in the 
     core of the Sun by a small amount, describe how the 
     process of hydrostatic equilibrium would return the Sun 
     to its original state.  A diagram or "flow chart" might 
     be helpful.  Mention any changes in pressure, density, 
     size and temperature.

(6)  Spiral galaxies are so named because they have disks 
     with very bright blue spiral arms that define their 
     shape.

	(a)  (3 points)  Why would you expect to find most of 
	     the young stars in a spiral galaxy in the spiral 
	     arms themselves?
	(b)  (3 points)  Why do these stars tend to make the 
	     spiral arms appear blue?
	(c)  (3 points)  Why don't they tend to appear anywhere 
	     else in a spiral galaxy (two possible answers, 
	     just give one)?

(7)  Globular clusters are huge spherical clusters of stars 
     in the halo that seem to have formed very early in the 
     history of our galaxy.

	(a)  (2 points)  Would you expect globular clusters to 
	     be "rich" with metals (high metallicity) or "poor"
	     in metals relative to our Sun?
	(b)  (7 points)  Explain your answer to (a).

(8)  The corona is an incredibly hot gas that surrounds the 
     Sun like a halo.  When we observe this gas, we find 
     that it is almost completely ionized.

	(a)  (4 points)  The corona is as hot as the Sun's 
	     core, yet no nuclear reactions are taking place in 
	     the corona.  Why this is true?
	(b)  (5 points)  Explain why the corona is almost 
	     completely ionized (assume we know already why it 
	     is so incredibly hot...very few particles share a 
	     great deal of energy).

(9)  The Inter-Stellar Medium (ISM) scatters the colors of 
     light in much the same way as our own atmosphere.  
     Assuming that the ISM is pretty much the same is the 
     Earth's atmosphere, answer the following...

	(a)  (3 points)  Would you expect a star that is deeply 
	     embedded inside a dust cloud to appear redder than 
	     normal or bluer or neither?  Explain why.
	(b)  (6 points)  Suppose there were a virtually 
	     invisible dust cloud between us and the star 
	     Sirius (a star astronomers claim to know an awful 
	     lot about).  One day, someone announces that they 
	     have discovered this ISM cloud.  How would our 
	     estimates of the temperature and mass of Sirius 
	     change and why?

(10)  A star undergoes a supernova very shortly after the 
      fusion of iron begins in the core.

	(a)  (5 points)  Explain why iron fusion in the core 
	     results in a supernova by describing the mechanism 
	     involved in a few simple steps.
	(b)  (4 points)  The element gold has an atomic number 
	     somewhat higher than iron.  Based on this fact, 
	     what can you say about where all the gold in the 
	     Universe must have formed?  Briefly explain how 
	     you know this.

(11)  Name two pieces of experimental evidence that lead us 
      to believe in the existence of dark matter, and explain 
      how the evidence points to the existence of dark 
      matter.  Do not explain two similar pieces of evidence.

(12)  We conclude a great deal from some very basic 
      observations of the Universe.  One such example is the 
      observation that the night sky is dark.  Assuming the 
      Universe is homogeneous (evenly distributed throughout 
      space), explain what basic conclusion we can draw from 
      the fact that the night sky is dark.

(13)  From our observations, we should be eventually be able 
      to determine the ultimate fate of the Universe (though 
      probably not in your lifetime).

	(a)  (5 points)  Why does the average density of the 
	     Universe determine whether the Universe will 
	     expand forever?
	(b)  (4 points)  What role does dark matter play in 
	     this problem?

(14)  The release of the Microwave Background Radiation 
      (MBR) was coincident with another important event in 
      the history of the Universe.

	(a)  (3 points)  What was happening at the same time as 
	     the release of the MBR?
	(b)  (6 points)  Why would we expect these two events 
	     to coincide?