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Chapter 27
Stars and Galaxies
Review
Choose the best response. Write the letter of that choice in the space provided.
1. In the majority of stars, the most common element is
a. oxygen.
b. helium.
c. hydrogen.
d. sodium.
c. green.
d. blue.
2. The color of the hottest stars is
a. red.
b. yellow.
3. Stars appear to move in circular paths around Polaris because
a. the earth rotates on its axis.
b. the earth orbits the sun.
c. the stars revolve around Polaris.
d. Polaris is the center of the Milky Way Galaxy.
4. The change in position of a nearby star compared with the position of a faraway star is
called
a. parallax.
b. red shift.
c. blue shift.
d. a Cepheid variable.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
5. The brightest stars have apparent magnitudes that are
a. over +20.
c. between +1 and +9.
b. between +10 and +19.
d. negative numbers.
6. The absolute magnitude of a star is
a. the relative brightness of the star.
b. the true brightness of the star.
c. the comparative brightness of the star.
d. the apparent brightness of the star.
7. A protostar becomes a star when it begins to
a. develop a red shift.
c. shrink and spin.
b. generate energy.
d. explode as a nova.
8. A main-sequence star generates energy by fusing
a. nitrogen into iron.
c. hydrogen into helium.
b. helium into carbon.
d. nitrogen into carbon.
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Chapter 27
Choose the best response. Write the letter of that choice in the space provided.
9. A dying star can shed some of its gases as a
a. planetary nebula.
c. globular cluster.
b. white dwarf.
d. supernova.
10. Black holes are difficult to locate because they
a. move very quickly.
c. have very low gravity.
b. do not give off light.
d. are far away from any stars.
11. A pattern of stars is called a
a. galaxy.
b. nebula.
c. pulsar.
d. constellation.
12. Stars appear in fixed locations in the sky because they
a. are so far from the earth.
c. are all moving toward the earth.
b. do not move.
d. are all in the same galaxy.
13. The basic types of galaxies are
a. spiral, elliptical, and irregular.
c. spiral, quasar, and pulsar.
b. barred, elliptical, and open.
d. open, binary, and globular.
14. Quasar formation is associated with
b. main-sequence stars.
d. the early universe.
Critical Thinking
Read each question or statement and answer it in the space provided.
1. If the spectrum of a star indicates that the star shines with a red light, approximately what is the
surface temperature of the star?
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a. nuclear fusion.
c. the explosion of a supernova.
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Chapter 27
Read each question or statement and answer it in the space provided.
2. Why are different constellations visible during different seasons of the year?
3. Explain why Polaris is considered to be a very bright star even though it is not a bright star in
the earth’s sky.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
4. Why does heat build up more rapidly in a massive protostar than in a less massive one?
5. Explain why an old main-sequence star will be composed of a higher percentage of helium than
will a young main-sequence star.
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Chapter 27
Read each question or statement and answer it in the space provided.
6. If all galaxies began to show blue shifts, what would this indicate about the fate of the universe?
Application
Read each question or statement and answer it in the space provided.
1. If you determined that a certain star displayed a large parallax, what could you say about its distance from the earth?
3. When looking through a nearby university’s telescope, you observed a galaxy that has no young
stars and contains little dust or gas. What kind of galaxy were you probably looking at?
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2. Suppose that a scientist has discovered a red-dwarf star. Describe the likely size and surface
temperature of such a star.
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Page 560: Discussion (Reinforcement)
Answers to Critical Thinking
To help students understand how astronomers can
infer the existence of black holes, use the example
of two ice skaters holding hands and spinning in a
circle. If one of the skaters were invisible, an
observer could still infer that two skaters were present by observing the effect the invisible skater
would have on the motion of the visible skater.
Similarly, astronomers detect black holes by their
gravitational effects on nearby stars, gas, or dust.
1. about 3,000°C
2. During each season of the year as the earth
revolves around the sun, some constellations are
obscured by the sun.
3. Polaris gives off a lot of light but is very distant
from the earth.
4. A massive protostar will have more bits of matter
that increase its pressure. This increased pressure
causes the temperature of the protostar to rise.
5. A main-sequence star converts hydrogen into
helium.
6. that it was decreasing
Page 565: EarthBeat
You may wish to explain that some quasars appear
to be moving away from the earth at 80 percent of
the speed of light. Have students calculate this speed
(300,000 km/s 0.80 = 240,000 km/s).
Small-Scale Investigation
Parallax (p. 551)
Science Process Skills: observing, interpreting,
inferring
Answers to Analysis and Conclusions
1. The plate does not actually change position,
although it does appear to move when it is
viewed from different locations.
2. The apparent change in position of the plate is
greater at short distances than it is farther away
because the angle formed by the observer’s new
line of sight and previous line of sight to the red
plate decreases with distance.
3. Answers will vary. A typical answer would be
that the stars exhibit an apparent motion over a
period of months that is similar to the apparent
motion of the red plate in this investigation. In
the case of the stars, the change in the observer’s
location is the result of the earth’s orbit around
the sun.
Chapter 27 Review
5. d
6. b
7. b
8. c
T132 Chapter 27
1. The star is relatively near the earth.
2. It would be small and cool.
3. elliptical
In-Depth Investigation
Star Magnitudes (pp. 568–569)
Approximate time: 1 class period
Objectives: to determine the effect of distance on
brightness and the relationship between temperature
and color
Skills: observing, measuring, calculating, predicting
Prelab Discussion
Before students begin this investigation, you may
want to review squaring numbers. Ask students to
explain the difference between absolute magnitude
and apparent magnitude. Students should be able to
explain why stars that appear to have equal brightness are not always the same distance from the
earth. Also discuss with students the reason the
flame of a candle ranges from blue, at the center of
the flame, to white-yellow, and then orange at the
edges. (The flame is hottest at the center, around the
burning wick.)
Teaching Strategies
Answers to Review
1. c
2. d
3. a
4. a
Answers to Application
9. d
10. b
11. d
12. a
13. a
14. d
1. Because of the amount of equipment used in this
investigation, have students work in groups of
two or three.
2. To prepare the wire to be used by the students,
use a pair of electrician’s wire strippers. If they
are unavailable, use a single-edged razor blade or
mat knife to cut the wires to the proper lengths,