Chapter 16 Review Questions


1.  What does the Milky Way look like in the night sky?


2.  How do we know our Galaxy is a flat disk?


3.  How did Shapley deduce the Milky Way’s size and the Sun’s position in it?


4.  Draw a sketch of the Milky Way Galaxy and label its major components.  Where is the Sun in the 

     Milky Way?


5.  Roughly how big in diameter is our Galaxy, and how much mass does it contain?


6.  What are some differences between Pop I and Pop II stars?


7.  Summarize the differences between open and globular clusters.  Are both still forming today in  

     the Milky Way?


8.  How do we know interstellar matter exists?  What different kinds and forms are there?


9.  How do we know that some interstellar matter is dust?  What is the other main category of 

     interstellar matter?


10.  How does interstellar dust affect our observations of stars, the Milky Way, and other galaxies?  

      What is the zone of avoidance?


11.  What is the difference between an emission and a reflection nebula?


12.  What are some ways that we know cold clouds of gas exist in space?


13.  What evidence makes astronomers conclude the Milky Way has spiral arms?


14.  How is star formation related to spiral arms?


15.  How can we determine the Milky Way’s diameter?


16.  How can we determine the Milky Way’s mass?


17.  What is meant by dark matter?  Why do astronomers conclude the Milky Way may contain such

      as yet unobserved material?


18.  What is the evidence for a black hole at the center of the Milky Way?  How does it compare to

       the black holes discussed in chapter 15?


19.  Describe one model for the origin of the Milky Way.  How does this model explain the difference

      between Pop I and Pop II stars?


20.  How do Mergers affect the evolution of the Milky Way?


21.  What is meant by Pop III stars?



Chapter 17 Review Questions


1.  What are the three main types of galaxies?  How do the basic galaxy types differ in shape, stellar

     content, and interstellar matter?


2.  Why is it not surprising that elliptical galaxies contain mostly Pop II stars?


3.  Explain several ways astronomers measure the distance to nearby galaxies.  Why is it important

     to know the distance?


3.  Explain several ways astronomers measure the distance to nearby galaxies.  Why is it important

     to know the distance?


4.  What is the Hubble law?  In what situations does Hubble’s law not apply?


5.  Why are galaxy collisions of interest?


6.  What happens to the stars when two galaxies collide?


7.  What are the three main types of active galaxies?  List the main characteristics of each.


8.  Sketch of a radio galaxy illustrating its structure.  Why do astronomers call these objects “radio



9.  What process generates the radio emission in radio galaxies?


10.  What is the evidence that quasars are very distant?


11.  How is it known that active galaxies have small core regions?


12.  What mechanism has been suggested as powering active galaxies?


13.  How might a large black hole form in a galaxy’s core?


14.  What is the Local Group, and why is it a group and not a cluster?


15.  What are some differences between clusters that contain large and small numbers of galaxies?


16.  What is the Local Supercluster?  How many clusters night be in a supercluster and how big is



17.  What is a void?


18.  What does the large-scale structure of the Universe look like?  How do astronomers study it?


19.  How do astronomers measure the mass of a galaxy?

20.  What is meant by dark matter?  What observations support its existence?  What types have been



21.  What is a gravitational lens?  What can observations of lenses tell us about clusters?


22.  What is the apparent ratio of dark matter to normal matter in a typical galaxy?  In a cluster of




Chapter 18 Review Questions


1.  Why do astronomers think that the Universe is expanding?


2.  What is meant by the age of the Universe?  How old is the Universe?  How is its age found?


3.  How can there be no center to the Universe?


4.  What is Olbers’ paradox?


5.  What is meant by a cosmic horizon?


6.  Is our cosmic horizon the same as that of beings in another galaxy?  Why?


7.  What does “light travel time distance” mean?


8.  What happened at the recombination era?  Why is this important?


9.  What is the cosmic microwave background?  What is its origin?


10.  Why do astronomers think that the early Universe was hot and dense?


11.  According to the Big Bang theory, what were the major eras in the history of the Universe? 

      What was the Universe like to each of them?  Approximately how long did each last?


12.  How was helium formed from hydrogen in the early Universe?


13.  Why is Einstein’s equation for the for the equivalence of mass and energy important when

      thinking about the early Universe?


14.  What do astronomers mean when they say that the Universe if flat?  What are the other



15.  What evidence do astronomers have that the Universe is flat?


16.  What is meant by inflation in cosmology?


17.  What problems of the Big Bang theory are resolved by inflationary models?



18.  What role does the cosmological constant play in cosmology?  Is this the same rule Einstein

      originally created it for?  What evidence makes astronomers think it may exist?


19.  What determines whether the Universe will expand forever or recollapse?  Explain what the

       critical density is.


20.  What is dark energy?  What does its presence imply for the future of the Universe?