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 WayÕs
size and the SunÕs 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 WayÕs diameter?
16. How can we determine the Milky WayÕs
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 HubbleÕs 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 ÒradioÓ
galaxies?
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
galaxyÕs 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
one?
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
proposed?
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
galaxies?
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 OlbersÕ
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 Òlight travel time distanceÓ
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 EinsteinÕs 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
possibilities?
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?