A101U Mid-Term 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 11 you 
want me to grade (you may "x" out the 3 that you don't 
want me to grade, if you wish).  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 1-2 sentences with an 
accompanying diagram.  In some cases, you will just be 
asked to fill in missing parts of a given 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.

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.

Please try to be concise when answering the 
questions.  Since you have at least 10 minutes to look 
at each of the 14 questions, stop to think about each 
one before you start writing.  Remember:  this exam 
will measure your ability not only to understand the 
concepts but also your ability to effectively 
communicate that understanding to me.  Write carefully 
and clearly.  If you write too much about a given 
question, that's fine.  I won't count off for your 
writing too much UNLESS you say something that is 
wrong.

If you need more paper at some point during the 
exam, raise your hand.  Likewise, if you have any 
questions, raise your hand and I will help you.

When everyone has a copy of the mid-term and we 
have finished going over these instructions, you may 
turn the cover page over and begin.  Note that each 
page has questions on both sides.

(1)  The diagram below shows the path of the Sun in the sky 
     from Pago Pago for March 21, June 21, September 21, and 
     December 21 (the equinoxes and solstices).  Note that 
     the South Celestial Pole is up in the sky,.  

	(a)  (6 points)  Label each of the three paths as 
	     "December 21 solstice," "Equinox," or "June 21 
	     solstice."
	(b)  (3 points)  Determine the latitude of Pago Pago 
	     and fill this information in below the diagram.  
	     Indicate South or North latitude in your answer.

[Diagram not included in ASCII version]

(2)  A siderial day is the amount of time it takes for a 
     star to travel in a complete circle around the sky.  A 
     solar day is the amount of time it takes for the Sun to 
     travel in a complete circle around the sky.  Which is 
     shorter, the siderial or solar day?  Draw a diagram to 
     help explain your answer.

(3)  We found in homework #1 that the angular size of the 
     Moon over the course of a month gets larger and 
     smaller.

	(a)  (4 points)  How does this fact help to explain why 
	     some solar eclipses are total and some are annular 
	     (ring of sunlight still visible around Moon)?
	(b)  (5 points)  Would we expect the Moon to be moving 
	     faster or slower in its orbit when its angular 
	     size is the largest?  Explain your answer.
(4)  Tides.

	(a)  (5 points)  Draw a diagram along with an 
	     explanation of how the Moon generates tides on 
	     both the near and far sides of the Earth.
	(b)  (4 points)  Would we expect higher or lower tides 
	     during an eclipse?     Explain why.

(5)  Spectral Lines.

	(a)  (5 points)  Why does each different element emit 
	     its own unique pattern of spectral lines?
	(b)  (4 points)  Would you expect Helium and singly 
	     ionized Helium (Helium with only one electron, 
	     rather than two) to have the same spectrum?  
	     Explain in very general terms why or why not.

(6)  Continuous radiation and Doppler shifts.

	(a)  (5 points)  Draw a rough graph of the continuous 
	     spectrum of a star like the Sun.  Use this diagram 
	     to explain why the Sun appears yellow to us.
	(b)  (4 points)  If the Sun were to start moving away 
	     from us with a large velocity, would it appear 
	     redder or bluer as seen from Earth?  Briefly 
	     explain why.

(7)  The upper limit of a planet's mass is set by the fact 
     that nuclear fusion will begin for planets with a very 
     large mass (hence, a large heat in its center).

	(a)  (5 points)  How do we define the lower limit of a 
	     planet's mass?
	(b)  (4 points)  How does it follow from this 
	     definition that all planets have cores of Iron or 
	     some other dense material?

(8)  One of the basic observations of our solar system is 
     that the orbits of the planets are all roughly coplanar 
     (they are all found close to the ecliptic, the plane of 
     Earth's orbit around the Sun).  Show how the 
     conservation of angular momentum and the collapse of 
     the solar nebula help to explain this observation.  Use 
     a diagram if you would like in order to help explain 
     your answer.

(9)  What are the two major reasons why the Jovians 
     (Jupiter, Saturn, Uranus, Neptune) are so much larger 
     than the terrestrials (Mercury, Venus, Earth, Mars)?

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

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

(11)  The Kirkwood gaps in the asteroid belt refer to a lack 
      of asteroids with periods that are very close to 
      integer ratios of Jupiter's period (2:1, 3:1, 3:2, 
      etc).

	(a)  (6 points)  Describe how an asteroid with half the 
	     period of Jupiter (say, 6 years as opposed to 
	     Jupiter's 12 year period) would have its orbit 
	     affected by Jupiter.
	(b)  (3 points)  Explain briefly how this process 
	     serves to keep the Earth in danger of giant 
	     impacts throughout its history.

(12)  In the film last week, we saw that two Astronomers had 
      used Infrared detectors to see a dusty disk around the 
      star Beta Pictoris.

	(a)  (5 points)  Why is this seen as possible evidence 
	     of another planetary system around that star?
	(b)  (4 points)  What is one other reason that Infrared 
	     technology is seen as so promising in attempts to 
	     directly image other planetary systems?

(13)  Suppose I were trying to measure the number of steps 
      it takes to walk across the 520 bridge between Seattle 
      and Redmond.  I decide that I want to take one 
      measurement for each day of the experiment.  
      Furthermore, I don't really like walking with the wind 
      blowing water and dirt in my face so I decide to only 
      walk across the bridge in the same direction as the 
      wind each day (assume the wind is blowing out of the 
      East on random days just as often as it is blowing out 
      of the West).

	(a)  (5 points)  Would my estimate of the number of 
	     steps it takes to walk across the bridge come any 
	     closer to the true number of steps if I were to 
	     repeat the experiment over the course of 100 days?  
	     Explain.
	(b)  (4 points)  What is one way I could improve my 
	     methods to get closer to the true value of the 
	     number of steps it takes to get across the bridge?

(14)  The four most common sources of scientific knowledge 
      are:  Personal experience, authority, testimony of a 
      trusted friend and revelation.  Which one of these four 
      sources do you see as the most reliable?  Explain why 
      you choose this and give an example where you have 
      determined some piece of knowledge using this method 
      over one of the others.