A101U Final Examination -- Autumn 1993

Instructions:  This exam consists of 18 short answer 
questions.  Answer 14 of the 18 short questions on the 
exam or the paper I will provide you.  If you answer 
more than 14 of the 18 short questions, mark the 4 you 
DON'T want me to grade(with a big "x" or 
something...just be unambiguous).  If you have more 
than 14 questions answered and have left me no marks, I 
will grade the first 14.  

The questions are worth 7 points each.  I expect 
answers of 2-5 sentences or 1-3 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 10 minutes per 
question (out of 14 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 January.  The final exam will be graded 
Tuesday with exam and course grades posted on the wall 
outside my office (Johnson 216) by Wednesday.  I will 
be around most of the day Wednesday to answer questions 
about your grades and your final exam.  After that, I 
will be gone until January 3rd, but I will be more than 
happy to discuss the course and your grade with you at 
that time.

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)  Would you classify this problem as a random or 
	     systematic error?  (2 points) 
	(b)  Explain by stating how this fits with the 
	     definition for the type of error you chose. (2 
	     points)
	(c)  Without observing any more galaxies, how could you 
	     eliminate this error in your sample?  It is 
	     possible!  (3 points)

(2)  The current most favored theory for the origin of the 
     Earth's Moon is that the Earth was struck by a Mars-
     sized object soon after its formation.
	(a)  Besides the fact that it is extremely unlikely for 
	     the Earth to "capture" an object the size of the 
	     Moon gravitationally, what is one other property 
	     of the Earth-Moon system that the capture theory 
	     fails to explain?  (3 points)
	(b)  How does the giant impact theory explain this 
	     detail?  (4 points)

(3)  Plots of continuous spectra of stars (intensity or 
     energy emitted vs. wavelength) help us determine their 
     temperatures.
	(a)  Plot a rough graph of the continuous spectrum for 
	     the Sun, showing where the visible region of the 
	     spectrum, the blue end of the spectrum,and the red 
	     end fall on the x-axis with a label. (3 points)
	(b)  Explain how this diagram tells us that the Sun is 
	     yellow in color. (2 points)
	(c)  At sunset, the Sun's light is passing through a 
	     longer distance in our atmosphere from our 
	     perspective.  Explain in words or with your 
	     diagram in (a) why the Sun appears red at sunset.  
	     (2 points)

(4)  Measures of spectral line properties can tell us much a 
     great deal about stars.
	(a)  Explain how the rotation of a star can lead to 
	     broadening of a spectral line via Doppler 
	     shifting.  (4 points)
	(b)  Explain how two identical stars, each rotating 
	     with the same speed, can display different amounts 
	     of "Doppler broadening" (assume one has none and 
	     the other has a lot for your example).  (3 points)

(5)  Of all the planets in the solar system, Jupiter has a 
     composition most like the Sun.
	(a)  What are the two elements making up the bulk of 
	     Jupiter's mass?  (2 points)
	(b)  What is the major reason that these elements are 
	     not found on Earth (describe how and why the Earth 
	     loses these elements)?  (5 points)

(6)  The diagram below represents a view of the sky from a 
     major city.
	(a)  Which city do you suppose it accurately 
	     represents:  Anchorage (61 deg North latitude), San 
	     Antonio (29 deg North latitude) or Kampala, Uganda 
	     (0 deg latitude)?  (2 points)
	(b)  Label the solar paths on the diagram with the 
	     proper seasons (summer, fall, winter, spring).  (2 
	     points)
	(c)  Explain which season has the longest days simply 
	     by using the information in the diagram.  (3 
	     points)

(7)  Though the Earth and Venus started with roughly the 
     same atmospheric composition, they rapidly diverged due 
     to the hotter temperatures on Venus.
	(a)  How does liquid water help to keep the Earth from 
	     becoming a greenhouse like Venus?  (3 points)
	(b)  What happened to the water vapor that drifted up 
	     to the upper layers of Venus' atmosphere (a two-
	     step process)?  (4 points)
(8)  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.  (7 points)

(9)  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)  The corona is as hot as the Sun's core, yet no 
	     nuclear reactions are taking place in the corona.  
	     Why this is true?  (3 points)
	(b)  Explain why the corona is so ionized (assume we 
	     know already why it is so incredibly hot...very 
	     few particles share a great deal of energy).  (4 
	     points)

(10)  Red Giant stars have cores of degenerate Helium and a 
      shell surrounding the inert core that is undergoing 
      Hydrogen fusion.  
	(a)  Why does this result in the puffing out of the 
	     star's envelope?  (4 points)
	(b)  Explain why you would expect the star to grow even 
	     larger as it approaches the Helium ignition stage.  
	     (3 points)

(11)  Another way to get information out of a spectrum 
      besides looking at individual lines is by looking at 
      the strengths of various lines of a given element.
	(a)  Why do some stars show the presence of ionized 
	     Helium (mostly stars about 50% or more hotter than 
	     the Sun) while others do not, assuming all stars 
	     have Helium of some kind in their atmospheres?  (3 
	     points)
	(b)  How can we use the ratio of ionized vs. neutral 
	     (or un-ionized) Helium to estimate the Temperature 
	     of a star?  (4 points)

(12)  Use a diagram to help you explain how we derive 
      distances to other stars using parallax.  You don't
      need exact trig formulae, just a general idea.  Be sure 
      to label everything on your diagram!  (7 points)

(13)  Spiral galaxies are so named because they have disks 
      with very bright blue spiral arms that define their 
      shape.
	(a)  Why would you expect to find most of the young 
	     stars in a spiral galaxy in the spiral arms 
	     themselves?  (2 points)
	(b)  Why do these stars tend to make the spiral arms 
	     appear blue?  (3 points)
	(c)  Why don't they tend to appear anywhere else in a 
	     spiral galaxy (two possible answers, just give 
	     one)?  (2 points)

(14)  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)  Would you expect globular clusters to be "rich" 
	     with metals (high metallicity) or "poor" in metals 
	     relative to our Sun?  (2 points)
	(b)  Explain your answer to (a).  (5 points)

(15)  Recent observations that elliptical galaxies tend to 
      be found in the centers of large clusters of galaxies 
      have suggested that elliptical galaxies are the result 
      of mergers of other galaxies (though this conclusion is 
      certainly debatable).
	(a)  Explain why this observation leads us to believe 
	     the "merger hypothesis." (3 points)
	(b)  Name another observation that leads us to believe 
	     that ellipticals form by mergers and explain why 
	     it makes us think this.  (4 points)

(16)  Two major observations that lead us to believe that 
      the Big Bang theory is correct are the Microwave 
      Background Radiation (MBR) and the expansion of the 
      Universe.  
	(a)  Explain what the MBR tells us about the early 
	     Universe (don't just say what it tells us).  (4 
	     points)
	(b)  Explain what the expansion of the Universe tells 
	     us about the early Universe.  (3 points)

(17)  From our observations, we should be eventually be able 
      to determine the ultimate fate of the Universe (though 
      probably not in your lifetime).
	(a)  Why does the average density of the Universe 
	     determine whether the Universe will expand 
	     forever?  (4 points)
	(b)  What role does dark matter play in this problem?  
	     (3 points)

(18)  The release of the Microwave Background Radiation 
      (MBR) was coincident with another important event in 
      the history of the Universe.
	(a)  What was happening at the same time as the release 
	     of the MBR?  (3 points)
	(b)  Why would we expect these two events to coincide?  
	     (4 points)