times the mass of the Sun. Because the Sun is of average mass, astronomers have concluded there are about 100 billion stars within the disk of the (15)




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Chapter 31.1

The mass located within the circle of the Sun’s orbit through the galaxy is about



(14) ___________ times the mass of the Sun. Because the Sun is of average

mass, astronomers have concluded there are about 100 billion stars within the disk of the (15) ___________. Astronomers have found evidence that much more mass exists in the outer galaxy. The stars and (16) ___________ that orbit in the outer disk are moving faster than

they would if the galaxy’s mass were concentrated near the (17) ___________ of the disk. Evidence indicates that as much as 90 percent of the galaxy’s mass is contained in the (18) ___________. This mass is not observed in the form of normal stars, and astronomers hypothesize that some of this unseen matter is in the form of dim (19) ___________ , such as white dwarfs, neutron stars, and black holes. The remainder of this mass, usually called (20) ___________ , is a mystery. Studies of the motion of stars that orbit close to Sagittarius A* indicate that this area has about (21) ___________ times the mass of the Sun, but is smaller than our solar system. Astronomers believe that Sagittarius A* is a ___________ (22) that glows brightly because of the hot gas surrounding it and spiraling into it.
Chapter 31.3

The study of the universe, including its current nature, its origin, and its evolution is called (1) ________. The fact that the universe is (2) ) ________ implies that it had a beginning. The theory that the universe began as a point and has been expanding ever since is called the (3) ) ________ theory. Not all astronomers agree that the universe had a beginning. The (4) ) ______________ theory proposes that the universe looks the same on large scales to all observers and that it has always looked that way. Supporters of this theory propose that new (5) ) ________ is created and added to the universe. Therefore, the overall (6) ) ________ of the universe doesn’t change.

According to the more accepted theory, the Big Bang Theory, if the universe began in a highly (7) ________ state, it would have been very hot, and the high temperatures would have filled it with (8) ) ________. As the universe expanded and cooled, the radiation would have been shifted by the (9) ) ________ effect to lower energies and longer wavelengths. In 1965, scientists discovered a persistent (10) ) ________ in their radio antenna. The noise was caused by weak radiation called the (11) ) ________. It appeared to come from all directions in space and corresponded to an emitting object having a temperature of about (12) ) ________ , which is close to the temperature predicted by the Big Bang theory. An orbiting observatory called the (13) ) ________ , launched in 1989, mapped the radiation in detail.

B

Chapters 31.1, 31.2, 31.3

1. The question about other objects existing in the sky was answered by Edwin Hubble in 1924.

What did he discover in the Great Nebula in the Andromeda constellation?



a. Cepheid variable stars b. RR Lyrae variables c. a supernova d. a black hole
2. Disklike galaxies with spiral arms are divided into which of the following two subclasses?

a. normal spirals and flat spirals b. flat spirals and barred spirals

c. normal spirals and barred spirals d. loose spirals and flat spirals
3. Galaxies that are not flattened into disks and do not have spiral arms are called

a. dwarf galaxies. b. elliptical galaxies. c. barred elliptical galaxies. d. nebular galaxies.
4. Galaxies that do not fit into the spiral or elliptical classifications are called

a. dwarf galaxies. b. Hubble galaxies. c. barred galaxies. d. irregular galaxies.

In your textbook, read about groups and clusters of galaxies.
For each statement, write true or false.

5. Most galaxies are spread evenly throughout the universe. __________

6. The Milky Way belongs to a small cluster of galaxies called the Local Group. _________

7. The Milky Way and the Andromeda Galaxy are two of the smallest members of the Local Group. _________

8. When galaxies move away from each other, they form strangely shaped galaxies or galaxies with more than one nucleus. __________

9. Studies of clusters of galaxies provide astronomers with the strongest evidence

that most of the matter in the universe is visible and accounted for. __________


10. What are the three possible outcomes for the universe?

a. open universe, closed universe, and flat universe b. expanding universe, closed universe, and flat universe

c. open universe, closed universe, and static universe d. open universe, barred universe, and flat universe
11. All three possible outcomes for the universe are based on the premise that the rate

of expansion has



a. remained the same since the beginning of the universe. b. slowed down since the beginning of the universe.

c. increased since the beginning of the universe. d. doubled since the beginning of the universe.
12. The total amount of matter in the universe is expressed in terms of the

a. critical density of matter. b. average density of matter.

c. average critical density of matter. d. absolute density of matter.
13. Observations of visible galaxies reveal a(n)

a. average density equal to critical density. b. average density much less than critical density.

c. absolute density greater than average critical density. d. critical density much less than average density.
14. Evidence suggests that the universe contains a great amount of

a. visible matter. b. invisible matter. c. mystery matter. d. dark matter.
15. By measuring redshifts of the most remote galaxies, it is possible for astronomers to

determine the



a. Doppler shifts. b. expansion rate of long ago.

c. absolute magnitudes. d. apparent magnitudes.
16. The universe began as a fluctuation in a vacuum and expanded very rapidly for a

fraction of a second, according to the



a. inflationary universe model. b. deceleration model.

c. steady-state model. d. flat universe model.
17. When the rate of expansion of the universe is known, it is possible to calculate the

a. date the universe will end. b. distance to each galaxy.

c. date the universe began. d. age of the universe.
18. Based on the best value for H that has been calculated, the age of the universe is

hypothesized to be about



a. 1.3 billion years. b. 13 billion years.

c. 13 million years. d. 13 trillion years.

Chapter 31.1

The mass located within the circle of the Sun’s orbit through the galaxy is about

(14) 100 billion times the mass of the Sun. Because the Sun is of average

mass, astronomers have concluded there are about 100 billion stars within the disk of the (15) galaxy. Astronomers have found evidence that much more mass exists in the outer galaxy. The stars and (16) gas cloud that orbit in the outer disk are moving faster than

they would if the galaxy’s mass were concentrated near the (17) center of the disk. Evidence indicates that as much as 90 percent of the galaxy’s mass is contained in the (18) halo. This mass is not observed in the form of normal stars, and astronomers hypothesize that some of this unseen matter is in the form of dim (19) stellar remnant, such as white dwarfs, neutron stars, and black holes. The remainder of this mass, usually called (20) dark matter, is a mystery. Studies of the motion of stars that orbit close to Sagittarius A* indicate that this area has about (21) 2.6 million times the mass of the Sun, but is smaller than our solar system. Astronomers believe that Sagittarius A* is a super massive black hole (22) that glows brightly because of the hot gas surrounding it and spiraling into it.
Chapter 31.3

The study of the universe, including its current nature, its origin, and its evolution is called (1) cosmology. The fact that the universe is (2) expanding implies that it had a beginning. The theory that the universe began as a point and has been expanding ever since is called the (3) big bang theory. Not all astronomers agree that the universe had a beginning. The (4) steady state theory proposes that the universe looks the same on large scales to all observers and that it has always looked that way. Supporters of this theory propose that new (5) matter is created and added to the universe. Therefore, the overall (6) density of the universe doesn’t change.

According to the more accepted theory, the Big Bang Theory, if the universe began in a highly (7) compressed state, it would have been very hot, and the high temperatures would have filled it with (8) radiation. As the universe expanded and cooled, the radiation would have been shifted by the (9) Doppler effect to lower energies and longer wavelengths. In 1965, scientists discovered a persistent (10) background radiation in their radio antenna. The noise was caused by weak radiation called the (11) cosmic background radiation It appeared to come from all directions in space and corresponded to an emitting object having a temperature of about (12) 2.7 Kelvin, which is close to the temperature predicted by the Big Bang theory. An orbiting observatory called the (13) cosmic background explorer, launched in 1989, mapped the radiation in detail.

B

Chapters 31.1, 31.2, 31.3

1. The question about other objects existing in the sky was answered by Edwin Hubble in 1924.

What did he discover in the Great Nebula in the Andromeda constellation?



a. Cepheid variable stars b. RR Lyrae variables c. a supernova d. a black hole
2. Disklike galaxies with spiral arms are divided into which of the following two subclasses?

a. normal spirals and flat spirals b. flat spirals and barred spirals

c. normal spirals and barred spirals d. loose spirals and flat spirals
3. Galaxies that are not flattened into disks and do not have spiral arms are called

a. dwarf galaxies. b. elliptical galaxies. c. barred elliptical galaxies. d. nebular galaxies.
4. Galaxies that do not fit into the spiral or elliptical classifications are called

a. dwarf galaxies. b. Hubble galaxies. c. barred galaxies. d. irregular galaxies.

In your textbook, read about groups and clusters of galaxies.
For each statement, write true or false.

5. Most galaxies are spread evenly throughout the universe. False

6. The Milky Way belongs to a small cluster of galaxies called the Local Group. True

7. The Milky Way and the Andromeda Galaxy are two of the smallest members of the Local Group. False

8. When galaxies move away from each other, they form strangely shaped galaxies or galaxies with more than one nucleus. False

9. Studies of clusters of galaxies provide astronomers with the strongest evidence

that most of the matter in the universe is visible and accounted for False


10. What are the three possible outcomes for the universe?

a. open universe, closed universe, and flat universe b. expanding universe, closed universe, and flat universe

c. open universe, closed universe, and static universe d. open universe, barred universe, and flat universe
11. All three possible outcomes for the universe are based on the premise that the rate

of expansion has



a. remained the same since the beginning of the universe. b. slowed down since the beginning of the universe.

c. increased since the beginning of the universe. d. doubled since the beginning of the universe.
12. The total amount of matter in the universe is expressed in terms of the

a. critical density of matter. b. average density of matter.

c. average critical density of matter. d. absolute density of matter.
13. Observations of visible galaxies reveal a(n)

a. average density equal to critical density. b. average density much less than critical density.

c. absolute density greater than average critical density. d. critical density much less than average density.
14. Evidence suggests that the universe contains a great amount of

a. visible matter. b. invisible matter. c. mystery matter. d. dark matter.
15. By measuring redshifts of the most remote galaxies, it is possible for astronomers to

determine the



a. Doppler shifts. b. expansion rate of long ago.

c. absolute magnitudes. d. apparent magnitudes.
16. The universe began as a fluctuation in a vacuum and expanded very rapidly for a

fraction of a second, according to the



a. inflationary universe model. b. deceleration model.

c. steady-state model. d. flat universe model.
17. When the rate of expansion of the universe is known, it is possible to calculate the

a. date the universe will end. b. distance to each galaxy.

c. date the universe began. d. age of the universe.
18. Based on the best value for H that has been calculated, the age of the universe is

hypothesized to be about



a. 1.3 billion years. b. 13 billion years.

c. 13 million years. d. 13 trillion years.


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