Question 1

Interstellar absorption lines are narrow primarily because:

Accepted Answer

A) there is very little interstellar matter. 
B) molecules always produce narrow absorption lines. 
C) most of the matter is ionized, and atoms moving fast produce sharp lines. 
D) the matter is at a low temperature, and atoms are almost still. 
E) All of the above are correct. 
A) there is very little interstellar matter. 
B) molecules always produce narrow absorption lines. 
C) most of the matter is ionized, and atoms moving fast produce sharp lines. 
D) the matter is at a low temperature, and atoms are almost still. 
E) All of the above are correct. D

Question 2

Interstellar gas is composed of:

Accepted Answer

A) only hydrogen. 
B) 90% hydrogen, 9% helium by weight. 
C) 10% hydrogen, 90% helium by numbers of atoms. 
D) some hydrogen, but mainly carbon dioxide. 
E) ammonia, methane, and water vapor. 
A) only hydrogen. 
B) 90% hydrogen, 9% helium by weight. 
C) 10% hydrogen, 90% helium by numbers of atoms. 
D) some hydrogen, but mainly carbon dioxide. 
E) ammonia, methane, and water vapor. B

Question 3

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. A

Question 4

The average temperature of the typical dark dust cloud is about:

Accepted Answer

A) 0 K. 
B) 2.73 K. 
C) 100 K. 
D) 3,000 K. 
E) 6,000 K. 
A) 0 K. 
B) 2.73 K. 
C) 100 K. 
D) 3,000 K. 
E) 6,000 K.

Question 5

Why is 21-cm radiation so important to the study of interstellar matter and the Galaxy?

Accepted Answer

A) It helps locate the galactic core in Sagittarius. 
B) Emitted by hydrogen, it passes through interstellar dust and lets us map the entire Galaxy. 
C) Emitted by carbon monoxide, it passes through interstellar gas and lets us see places rich inorganic molecules around the Galaxy. 
D) It is emitted by most stars, enabling astronomers to map the entire Galaxy. 
E) It is emitted only in hot regions of star formation, so the pattern of the spiral arms of theGalaxy can be mapped. 
A) It helps locate the galactic core in Sagittarius. 
B) Emitted by hydrogen, it passes through interstellar dust and lets us map the entire Galaxy. 
C) Emitted by carbon monoxide, it passes through interstellar gas and lets us see places rich inorganic molecules around the Galaxy. 
D) It is emitted by most stars, enabling astronomers to map the entire Galaxy. 
E) It is emitted only in hot regions of star formation, so the pattern of the spiral arms of theGalaxy can be mapped.

Question 6

Explain the colors of emission nebulae.

Accepted Answer

The predominant bright red is the emissi

Question 7

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 8

Emission nebulae like M42 occur only near stars that emit large amounts of:

Accepted Answer

A) visible light. 
B) microwaves. 
C) ultraviolet radiation. 
D) infrared heat. 
E) X-rays and gamma rays. 
A) visible light. 
B) microwaves. 
C) ultraviolet radiation. 
D) infrared heat. 
E) X-rays and gamma rays.

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

What does the polarization of starlight tell us about the dust grains and the Galaxy?

Accepted Answer

The Galaxy's magnetic field al

Question 11

The gas in the interstellar medium consists of mostly heavy elements.

Accepted Answer

A) True 
 B)False

Question 12

What are the properties of the neutral hydrogen gas that exists in the interstellar medium?

Accepted Answer

Neutral hydrogen dominates the compositi

Question 13

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 14

A cold region of dust which scatters the light of nearby stars produces a nebula which appears________ in color, such as the one encompassing the Pleiades cluster.

Accepted Answer

The answer of A cold region of dust which scatters...

Question 15

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 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 do "forbidden" lines reveal about interstellar space?

Accepted Answer

A) The density or pressure of this gas is much lower than can be produced in a laboratory. 
B) The laws of physics are not the same in space as they are on Earth. 
C) There are unknown elements in space that do not correspond to elements found on Earth. 
D) There are molecules found in meteorites and interstellar dust that are not found on Earth. 
E) All of the above are true. 
A) The density or pressure of this gas is much lower than can be produced in a laboratory. 
B) The laws of physics are not the same in space as they are on Earth. 
C) There are unknown elements in space that do not correspond to elements found on Earth. 
D) There are molecules found in meteorites and interstellar dust that are not found on Earth. 
E) All of the above are true.

Question 18

Some regions along the plane of the Milky Way appear dark because:

Accepted Answer

A) there are no stars in these areas. 
B) stars in that region are hidden by interstellar gas. 
C) stars in that region are hidden by dark dust particles. 
D) many brown dwarfs in those areas absorb light which they turn into heat. 
E) many black holes absorb all light from those directions. 
A) there are no stars in these areas. 
B) stars in that region are hidden by interstellar gas. 
C) stars in that region are hidden by dark dust particles. 
D) many brown dwarfs in those areas absorb light which they turn into heat. 
E) many black holes absorb all light from those directions.

Question 19

Which of the following describes the shape of dust particles, based on polarization of light?

Accepted Answer

A) diamonds 
B) cubes 
C) spheres 
D) disks 
E) rodlike 
A) diamonds 
B) cubes 
C) spheres 
D) disks 
E) rodlike

Question 20

Neutral hydrogen may be detected between the stars because it emits ________.

Accepted Answer

The answer of Neutral hydrogen may be detected between the...

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

Interstellar absorption lines are narrow primarily because:

Interstellar gas is composed of:

The overall dimming of starlight by interstellar matter is called:

The average temperature of the typical dark dust cloud is about:

Why is 21-cm radiation so important to the study of interstellar matter and the Galaxy?

Explain the colors of emission nebulae.

Why are dark dust clouds largely misnamed?

Emission nebulae like M42 occur only near stars that emit large amounts of:

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

What does the polarization of starlight tell us about the dust grains and the Galaxy?

The gas in the interstellar medium consists of mostly heavy elements.

What are the properties of the neutral hydrogen gas that exists in the interstellar medium?

Which statement about the dark nebulae is true?

A cold region of dust which scatters the light of nearby stars produces a nebula which appears________ in color, such as the one encompassing the Pleiades cluster.

What is the primary visible color of an emission nebula?

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

What do "forbidden" lines reveal about interstellar space?

Some regions along the plane of the Milky Way appear dark because:

Which of the following describes the shape of dust particles, based on polarization of light?

Neutral hydrogen may be detected between the stars because it emits ________.

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: Earths 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

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