Question 1

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

Accepted Answer

A) True 
 B)False

Question 2

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. 
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.

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

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 5

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 UV 
A)  Radio and infrared 
B)  visible only 
C)  UV and infrared 
D)  Radio and X-ray 
E)  Visible and UV

Question 6

Contrast the sizes of molecular clouds with emission nebulae.

Accepted Answer

The emission nebula are only a few light

Question 7

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 dust 
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 dust

Question 8

Dark nebulae are opaque to all wavelengths of electromagnetic radiation.

Accepted Answer

A) True 
 B)False

Question 9

Reflection nebulae usually appear red.

Accepted Answer

A) True 
 B)False

Question 10

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. 
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.

Question 11

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

Accepted Answer

A) True 
 B)False

Question 12

The overall dimming of starlight by interstellar matter is called:

Accepted Answer

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

Question 13

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)  radio 
A)  gamma rays 
B)  extreme ultraviolet 
C)  infrared 
D)  microwave 
E)  radio

Question 14

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. 
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.

Question 15

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

Accepted Answer

A) True 
 B)False

Question 16

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

Accepted Answer

The grain size of the dust is

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 dust 
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 dust

Question 18

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

Accepted Answer

In some cases,they are not thick enough

Question 19

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

Accepted Answer

These lines correspond to excited states

Question 20

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

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

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

Which statement about the dark nebulae is true?

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

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

Interstellar dust clouds are best observed at what wavelength?

Contrast the sizes of molecular clouds with emission nebulae.

What is the primary visible color of an emission nebula?

Dark nebulae are opaque to all wavelengths of electromagnetic radiation.

Reflection nebulae usually appear red.

Which statement is true about the interstellar medium?

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

The overall dimming of starlight by interstellar matter is called:

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

Why are dark dust clouds largely misnamed?

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

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

What two things are needed to create an emission nebulae?

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

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

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

Charting the Heavens: The Foundations of Astronomy

The Copernican Revolution: The Birth of Modern Science

Radiation: Information from the Cosmos

Spectroscopy: The Inner Workings of Atoms

Telescopes: The Tools of Astronomy

The Solar System: Comparative Planetology and Formation Models

Earth: Our Home in Space

The Moon and Mercury: Scorched and Battered Worlds

Venus: Earth's Sister Planet

Mars: A Near Miss for Life?

Jupiter: Giant of the Solar System

Saturn: Spectacular Rings and Mysterious Moons

Uranus and Neptune: The Outer Worlds of the Solar System

Solar System Debris: Keys to Our Origin

Exoplanets: Planetary Systems Beyond Our Own

The Sun: Our Parent Star

The Stars: Giants,Dwarfs,and the Main Sequence

Star Formation: A Traumatic Birth

Stellar Evolution: The Life and Death of a Star

Stellar Explosions: Novae,Supernovae,and the Formation of the Elements

Neutron Stars and Black Holes: Strange States of Matter

The Milky Way Galaxy: A Spiral in Space

Galaxies: Building Blocks of the Universe

Galaxies and Dark Matter: The Large-Scale Structure of the Cosmos

Cosmology: The Big Bang and the Fate of the Universe

The Early Universe: Toward the Beginning of Time

Life in the Universe: Are We Alone?

Filters