Question 1

Why are dark dust clouds largely misnamed?

Accepted Answer

A)   The cloud is an illusion, for the dust is evenly distributed around the Galaxy.
B)   Dust clouds do radiate energy, but not as much light as the stars do.
C)   It is ice, not dust, which make them look dark.
D)   They contain much more gas than dust.
E)   All of the above are correct.F) A) and D)
G) C) and D)

Question 2

What is the temperature of the gas in the dark dust clouds,and why is this important to molecule formation?

Accepted Answer

The gas is about 100...

Question 3

We look toward a cool star.How can we determine that there is an interstellar dust cloud between us and the star?

Accepted Answer

The temperature of the star is determine...

Question 4

The compositions of dark clouds can be determined through absorption spectra.

Accepted Answer

A) True 
 B)False

Question 5

The overall dimming of starlight by interstellar matter is called:

Accepted Answer

A)   extinction.
B)   reddening.
C)   absorption.
D)   emission.
E)   scattering.F) B) and D)
G) B) and C)

Question 6

In which wavelengths have the births of new stars been best mapped recently?

Accepted Answer

A)   gamma rays
B)   extreme ultraviolet
C)   infrared
D)   microwave
E)   radioF) A) and B)
G) D) and E)

Question 7

Explain how "forbidden" lines appear in spectra of emission nebulae.

Accepted Answer

These lines correspond to excited states...

Question 8

What is the primary visible color of an emission nebula?

Accepted Answer

A)   black, because of dust
B)   blue from the scattering of light off the tiny molecules
C)   blue due to ionized helium atoms
D)   red due to ionized hydrogen atoms
E)   red because of reddening by dustF) A) and B)
G) A) and C)

Question 9

If dark nebulae are really dark,how do we know they are there?

Accepted Answer

In some cases,they are not thick enough ...

Question 10

Which statement about the dark nebulae is true?

Accepted Answer

A)   Hydrogen and helium are the chief absorbing and scattering agents.
B)   They block the vast majority of radio waves from our Galaxy.
C)   They can be penetrated only with longer wavelengths such as radio and infrared.
D)   They comprise the majority of the mass of the Galaxy.
E)   They can be penetrated only with shorter waves, such as UV and X-ray.F) A) and B)
G) A) and C)

Question 11

The H I regions are mapped by the radiation created when an electron flips its spin.

Accepted Answer

A) True 
 B)False

Question 12

How can interstellar dust block starlight in spite of its extremely low density?

Accepted Answer

The grain size of the dust is ...

Question 13

Which statement is true about the interstellar medium?

Accepted Answer

A)   Gas contains a lot of carbon atoms.
B)   Dust blocks the longest electromagnetic wavelengths.
C)   Gas obscures the light from distant stars.
D)   We know more about the gas than the dust.
E)   Dust is spread uniformly through the galaxy.F) B) and E)
G) A) and E)

Question 14

Interstellar dust clouds are best observed at what wavelength?

Accepted Answer

A)   Radio and infrared
B)   visible only
C)   UV and infrared
D)   Radio and X-ray
E)   Visible and UVF) A) and C)
G) None of the above

Question 15

Contrast the sizes of molecular clouds with emission nebulae.

Accepted Answer

The emission nebula are only a few light...

Question 16

Why are so few molecules observed in visible light? Where are most observed,and why?

Accepted Answer

Few molecules,such as TiO,are durable en...

Question 17

What two things are needed to create an emission nebulae?

Accepted Answer

A)   interstellar gas and dust
B)   hydrogen fusion and helium ionization
C)   cool stars and much interstellar dust
D)   hot stars and interstellar gas, particularly hydrogen
E)   hydrogen gas and carbon dustF) A) and D)
G) C) and E)

Question 18

Reflection nebulae usually appear red.

Accepted Answer

A) True 
 B)False

Question 19

Dark nebulae are opaque to all wavelengths of electromagnetic radiation.

Accepted Answer

A) True 
 B)False

Question 20

A dark cloud can be detected if it happens to block the light emitted by more distant stars.

Accepted Answer

A) True 
 B)False

Exam 18: The Interstellar Medium: Gas and Dust among the Stars

What is the temperature of the gas in the dark dust clouds,and why is this important to molecule formation?

Correct AnswerverifiedThe gas is about 100...View AnswerShow Answer

Explain how "forbidden" lines appear in spectra of emission nebulae.

Correct AnswerverifiedThese lines correspond to excited states...View AnswerShow Answer

We look toward a cool star.How can we determine that there is an interstellar dust cloud between us and the star?

Correct AnswerverifiedThe temperature of the star is determine...View AnswerShow Answer

Which statement about the dark nebulae is true?

Correct AnswerverifiedShow Answer

Dark nebulae are opaque to all wavelengths of electromagnetic radiation.

Correct AnswerverifiedShow Answer

Why are so few molecules observed in visible light? Where are most observed,and why?

Correct AnswerverifiedFew molecules,such as TiO,are durable en...View AnswerShow Answer

In which wavelengths have the births of new stars been best mapped recently?

Correct AnswerverifiedShow Answer

Why are dark dust clouds largely misnamed?

Correct AnswerverifiedShow Answer

How can interstellar dust block starlight in spite of its extremely low density?

Correct AnswerverifiedThe grain size of the dust is ...View AnswerShow Answer

The overall dimming of starlight by interstellar matter is called:

Correct AnswerverifiedShow Answer

A dark cloud can be detected if it happens to block the light emitted by more distant stars.

Correct AnswerverifiedShow Answer

What two things are needed to create an emission nebulae?

Correct AnswerverifiedShow Answer

Reflection nebulae usually appear red.

Correct AnswerverifiedShow Answer

If dark nebulae are really dark,how do we know they are there?

Correct AnswerverifiedIn some cases,they are not thick enough ...View AnswerShow Answer

The compositions of dark clouds can be determined through absorption spectra.

Correct AnswerverifiedShow Answer

The H I regions are mapped by the radiation created when an electron flips its spin.

Correct AnswerverifiedShow Answer

Which statement is true about the interstellar medium?

Correct AnswerverifiedShow Answer

What is the primary visible color of an emission nebula?

Correct AnswerverifiedShow Answer

Contrast the sizes of molecular clouds with emission nebulae.

Correct AnswerverifiedThe emission nebula are only a few light...View AnswerShow Answer

Interstellar dust clouds are best observed at what wavelength?

Correct AnswerverifiedShow Answer

Correct Answer
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The gas is about 100...
View Answer

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These lines correspond to excited states...
View Answer

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The temperature of the star is determine...
View Answer

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Few molecules,such as TiO,are durable en...
View Answer

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The grain size of the dust is ...
View Answer

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In some cases,they are not thick enough ...
View Answer

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The emission nebula are only a few light...
View Answer

Correct Answer
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