Question 1

The speed of H I gas clouds can be found using the

Accepted Answer

A)  Doppler effect of radio signals. 
B)  21-cm spin-flip transition. 
C)  temperature of the clouds. 
D)  mass of the clouds. 
A)  Doppler effect of radio signals. 
B)  21-cm spin-flip transition. 
C)  temperature of the clouds. 
D)  mass of the clouds. A

Question 2

What causes the 21-cm radiation,and what is it useful for detecting?

Accepted Answer

When neutral hydrogen switches from a higher energy configuration of both the proton and the electron spinning in the same direction to a lower energy configuration with the proton and the electron spinning in opposite directions,a photon is emitted with a wavelength of 21-cm.This allows us to use this spectral line in the radio region to map clouds of H I,or neutral hydrogen.

Question 3

The Milky Way,in which the Sun resides,is an example of which type of galaxy?

Accepted Answer

A)  An elliptical galaxy 
B)  A normal spiral galaxy 
C)  A barred spiral galaxy 
D)  An irregular galaxy 
A)  An elliptical galaxy 
B)  A normal spiral galaxy 
C)  A barred spiral galaxy 
D)  An irregular galaxy C

Question 4

What atomic transition occurs in atoms of hydrogen gas in the galactic spiral arms to produce 21-cm radio emission?

Accepted Answer

A)  The change in the vibrational state of the H atoms in the H2 molecule 
B)  The transition from the n = 2 to n = 1 level in atomic hydrogen 
C)  The inversion of the electron spin relative to the proton spin,from parallel to anti-parallel 
D)  The change in rotation about an axis perpendicular to the molecular axis in the molecule H2 
A)  The change in the vibrational state of the H atoms in the H2 molecule 
B)  The transition from the n = 2 to n = 1 level in atomic hydrogen 
C)  The inversion of the electron spin relative to the proton spin,from parallel to anti-parallel 
D)  The change in rotation about an axis perpendicular to the molecular axis in the molecule H2

Question 5

Harlow Shapley's original estimate of the distance from the Sun to the galactic center was incorrect because it did not take interstellar extinction into account.This original estimate was

Accepted Answer

A)  too large because light scattering and absorption by dust made nearer stars look dim-as though they were more distant. 
B)  too large because scattering by dust made stars look redder-as though they were highly Doppler shifted and thus more distant. 
C)  too small because gas and dust tend to reflect light back into the path of the beam,thus making stars look brighter and nearer. 
D)  too large because scattering by dust made stars look redder-as though they were red giants of larger luminosity and thus farther away. 
A)  too large because light scattering and absorption by dust made nearer stars look dim-as though they were more distant. 
B)  too large because scattering by dust made stars look redder-as though they were highly Doppler shifted and thus more distant. 
C)  too small because gas and dust tend to reflect light back into the path of the beam,thus making stars look brighter and nearer. 
D)  too large because scattering by dust made stars look redder-as though they were red giants of larger luminosity and thus farther away.

Question 6

What fraction of the mass of our Galaxy is in a form that we have been able to see?

Accepted Answer

A)  About 10% 
B)  100%-all matter can be seen. 
C)  About 50% 
D)  About 90% 
A)  About 10% 
B)  100%-all matter can be seen. 
C)  About 50% 
D)  About 90%

Question 7

We cannot see the precise shape of the Milky Way Galaxy mainly because

Accepted Answer

A)  it is too large. 
B)  of interstellar dust and gas. 
C)  it contains too many stars. 
D)  we are inside of it. 
A)  it is too large. 
B)  of interstellar dust and gas. 
C)  it contains too many stars. 
D)  we are inside of it.

Question 8

In the halo of the Galaxy,there are no

Accepted Answer

A)  brown dwarf stars. 
B)  red dwarf stars. 
C)  white dwarf stars. 
D)  O and B stars. 
A)  brown dwarf stars. 
B)  red dwarf stars. 
C)  white dwarf stars. 
D)  O and B stars.

Question 9

The spiral arm structure of the Milky Way Galaxy has been measured and evaluated most effectively by observations of

Accepted Answer

A)  Lyman UV radiation from hot hydrogen gas. 
B)  observations of globular clusters in the halo of the Galaxy. 
C)  21-cm radiation from interstellar hydrogen and the positions of young stars. 
D)  Balmer emission lines of visible radiation from hydrogen. 
A)  Lyman UV radiation from hot hydrogen gas. 
B)  observations of globular clusters in the halo of the Galaxy. 
C)  21-cm radiation from interstellar hydrogen and the positions of young stars. 
D)  Balmer emission lines of visible radiation from hydrogen.

Question 10

When we measure the narrow line emissions of hydrogen at 21-cm radio wavelength along a particular line of sight through the disk of our Galaxy,we can tell the distances to different hydrogen clouds because

Accepted Answer

A)  clouds at different distances have different Doppler shifts due to the rotation of the Galaxy. 
B)  the farther away the gas cloud,the greater the delay in the arrival time of the 21-cm emission. 
C)  clouds that are farther away have smaller angular sizes. 
D)  the emission is weaker from clouds that are farther away. 
A)  clouds at different distances have different Doppler shifts due to the rotation of the Galaxy. 
B)  the farther away the gas cloud,the greater the delay in the arrival time of the 21-cm emission. 
C)  clouds that are farther away have smaller angular sizes. 
D)  the emission is weaker from clouds that are farther away.

Question 11

If the galactic center is now thought to contain a supermassive black hole,why is the Sun not falling into it under the black hole's extreme gravity?

Accepted Answer

A)  The inward force exerted on the Sun from the black hole is offset by the force exerted outward by the hidden "dark" matter beyond the Sun's orbit. 
B)  Its mass is so small that even this extreme mass concentration at the galactic center will not exert a significant force on it. 
C)  The Sun has sufficient velocity that it can orbit the galactic center in a circle. 
D)  The mutual gravitational forces of local stars in the Orion spiral arm are sufficient to overcome the strong inward force and keep the Sun moving in its orbit. 
A)  The inward force exerted on the Sun from the black hole is offset by the force exerted outward by the hidden "dark" matter beyond the Sun's orbit. 
B)  Its mass is so small that even this extreme mass concentration at the galactic center will not exert a significant force on it. 
C)  The Sun has sufficient velocity that it can orbit the galactic center in a circle. 
D)  The mutual gravitational forces of local stars in the Orion spiral arm are sufficient to overcome the strong inward force and keep the Sun moving in its orbit.

Question 12

Recent observations suggest that the Milky Way may

Accepted Answer

A)  be an irregular galaxy,with chaotic distribution of matter within it. 
B)  have vast stellar streams in a plane perpendicular to the galaxy's disk,formed by a collision of the Milky Way with another large spiral galaxy. 
C)  be an elliptical galaxy,with little structure. 
D)  have a central bar,formed by an elongation of the central bulge. 
A)  be an irregular galaxy,with chaotic distribution of matter within it. 
B)  have vast stellar streams in a plane perpendicular to the galaxy's disk,formed by a collision of the Milky Way with another large spiral galaxy. 
C)  be an elliptical galaxy,with little structure. 
D)  have a central bar,formed by an elongation of the central bulge.

Question 13

Much of the mass of our Galaxy appears to be in the form of "dark matter" of unknown composition.At present,this matter can be detected only because

Accepted Answer

A)  it absorbs light from distant galaxies and quasars and obscures them. 
B)  it emits synchrotron radiation. 
C)  its gravitational pull affects orbital motions of matter in the Galaxy. 
D)  it blocks out the light from distant stars in the plane of our Galaxy. 
A)  it absorbs light from distant galaxies and quasars and obscures them. 
B)  it emits synchrotron radiation. 
C)  its gravitational pull affects orbital motions of matter in the Galaxy. 
D)  it blocks out the light from distant stars in the plane of our Galaxy.

Question 14

Which of the following locations in our universe has been suggested as the site of a supermassive black hole?

Accepted Answer

A)  The center of the Ring Nebula in Lyra,an old star 
B)  The center of the Crab Nebula,an old supernova remnant 
C)  The center of the universe,as defined by the universal expansion of the observable universe 
D)  The center of our Galaxy 
A)  The center of the Ring Nebula in Lyra,an old star 
B)  The center of the Crab Nebula,an old supernova remnant 
C)  The center of the universe,as defined by the universal expansion of the observable universe 
D)  The center of our Galaxy

Question 15

The center of our Milky Way Galaxy can be observed most easily at which of the following wavelengths?

Accepted Answer

A)  Ultraviolet light. 
B)  Hydrogen Balmer H light. 
C)  Infrared and radio radiation. 
D)  Highly penetrating gamma rays. 
A)  Ultraviolet light. 
B)  Hydrogen Balmer H light. 
C)  Infrared and radio radiation. 
D)  Highly penetrating gamma rays.

Question 16

A rotation curve allows astronomers to calculate

Accepted Answer

A)  the size of the Galaxy. 
B)  the luminosity of the Galaxy. 
C)  the temperature of the Galaxy. 
D)  the mass of the Galaxy. 
A)  the size of the Galaxy. 
B)  the luminosity of the Galaxy. 
C)  the temperature of the Galaxy. 
D)  the mass of the Galaxy.

Question 17

Where in space would you look for a globular cluster?

Accepted Answer

A)  In the Milky Way halo,orbiting the galactic center in a long elliptical orbit 
B)  In the galactic disk,moving in a circular orbit around the galactic center 
C)  In the asteroid belt 
D)  Only in elliptical galaxies,because they are composed of old stars 
A)  In the Milky Way halo,orbiting the galactic center in a long elliptical orbit 
B)  In the galactic disk,moving in a circular orbit around the galactic center 
C)  In the asteroid belt 
D)  Only in elliptical galaxies,because they are composed of old stars

Question 18

Where are the youngest stars in the Galaxy?

Accepted Answer

A)  In the core 
B)  In the disk 
C)  In the halo 
D)  All of these have young stars. 
A)  In the core 
B)  In the disk 
C)  In the halo 
D)  All of these have young stars.

Question 19

What is microlensing?

Accepted Answer

A)  A minute shift in the apparent position of a star as an object passes in front of it 
B)  A slow brightening of a star as an object passes in front of it 
C)  The temporary disappearance of a star as an object passes in front of it 
D)  A gradual reduction in brightness of a star as an object passes in front of it 
A)  A minute shift in the apparent position of a star as an object passes in front of it 
B)  A slow brightening of a star as an object passes in front of it 
C)  The temporary disappearance of a star as an object passes in front of it 
D)  A gradual reduction in brightness of a star as an object passes in front of it

Question 20

The possible presence of a very large amount of unseen ("dark")matter in the halo of our Galaxy is deduced from the

Accepted Answer

A)  unexpected absence of luminous matter (stars,etc. )beyond a certain distance. 
B)  rotation curve of our Galaxy,which indicates higher than expected orbital speeds in the outer regions of the Galaxy. 
C)  rotation curve of our Galaxy,which shows that orbital speeds in the outer parts of the Galaxy decrease in a way that follows Kepler's law. 
D)  unexpected high amount of interstellar absorption in certain directions. 
A)  unexpected absence of luminous matter (stars,etc. )beyond a certain distance. 
B)  rotation curve of our Galaxy,which indicates higher than expected orbital speeds in the outer regions of the Galaxy. 
C)  rotation curve of our Galaxy,which shows that orbital speeds in the outer parts of the Galaxy decrease in a way that follows Kepler's law. 
D)  unexpected high amount of interstellar absorption in certain directions.

The speed of H I gas clouds can be found using the

What causes the 21-cm radiation,and what is it useful for detecting?

The Milky Way,in which the Sun resides,is an example of which type of galaxy?

What atomic transition occurs in atoms of hydrogen gas in the galactic spiral arms to produce 21-cm radio emission?

Harlow Shapley's original estimate of the distance from the Sun to the galactic center was incorrect because it did not take interstellar extinction into account.This original estimate was

What fraction of the mass of our Galaxy is in a form that we have been able to see?

We cannot see the precise shape of the Milky Way Galaxy mainly because

In the halo of the Galaxy,there are no

The spiral arm structure of the Milky Way Galaxy has been measured and evaluated most effectively by observations of

When we measure the narrow line emissions of hydrogen at 21-cm radio wavelength along a particular line of sight through the disk of our Galaxy,we can tell the distances to different hydrogen clouds because

If the galactic center is now thought to contain a supermassive black hole,why is the Sun not falling into it under the black hole's extreme gravity?

Recent observations suggest that the Milky Way may

Much of the mass of our Galaxy appears to be in the form of "dark matter" of unknown composition.At present,this matter can be detected only because

Which of the following locations in our universe has been suggested as the site of a supermassive black hole?

The center of our Milky Way Galaxy can be observed most easily at which of the following wavelengths?

A rotation curve allows astronomers to calculate

Where in space would you look for a globular cluster?

Where are the youngest stars in the Galaxy?

What is microlensing?

The possible presence of a very large amount of unseen ("dark")matter in the halo of our Galaxy is deduced from the

Predicting the Motions of the Stars, Sun, and Moon

Decoding the Hidden Messages in Starlight

Analyzing Scales and Motions of the Universe

Exploring Our Evolving Solar System

Uncovering Earths Systems

Exploring Terrestrial Surface Processes and Atmospheres

Observing the Dynamic Giant Planets

Looking for Life Beyond Earth

Probing the Dynamic Sun

Observing Properties of Distant Stars

Inferring Patterns in Star Life Cycles

Predicting the Violent End of the Largest Stars

Investigating Other Galaxies

Observing the Evolution of the Universe

Filters

Exam 13: Exploring Our Galaxy

The speed of H I gas clouds can be found using the

What causes the 21-cm radiation,and what is it useful for detecting?

The Milky Way,in which the Sun resides,is an example of which type of galaxy?

What atomic transition occurs in atoms of hydrogen gas in the galactic spiral arms to produce 21-cm radio emission?

Harlow Shapley's original estimate of the distance from the Sun to the galactic center was incorrect because it did not take interstellar extinction into account.This original estimate was

What fraction of the mass of our Galaxy is in a form that we have been able to see?

We cannot see the precise shape of the Milky Way Galaxy mainly because

In the halo of the Galaxy,there are no

The spiral arm structure of the Milky Way Galaxy has been measured and evaluated most effectively by observations of

When we measure the narrow line emissions of hydrogen at 21-cm radio wavelength along a particular line of sight through the disk of our Galaxy,we can tell the distances to different hydrogen clouds because

If the galactic center is now thought to contain a supermassive black hole,why is the Sun not falling into it under the black hole's extreme gravity?

Recent observations suggest that the Milky Way may

Much of the mass of our Galaxy appears to be in the form of "dark matter" of unknown composition.At present,this matter can be detected only because

Which of the following locations in our universe has been suggested as the site of a supermassive black hole?

The center of our Milky Way Galaxy can be observed most easily at which of the following wavelengths?

A rotation curve allows astronomers to calculate

Where in space would you look for a globular cluster?

Where are the youngest stars in the Galaxy?

What is microlensing?

The possible presence of a very large amount of unseen ("dark")matter in the halo of our Galaxy is deduced from the

Predicting the Motions of the Stars, Sun, and Moon

Decoding the Hidden Messages in Starlight

Analyzing Scales and Motions of the Universe

Exploring Our Evolving Solar System

Uncovering Earths Systems

Exploring Terrestrial Surface Processes and Atmospheres

Observing the Dynamic Giant Planets

Looking for Life Beyond Earth

Probing the Dynamic Sun

Observing Properties of Distant Stars

Inferring Patterns in Star Life Cycles

Predicting the Violent End of the Largest Stars

Investigating Other Galaxies

Observing the Evolution of the Universe

Filters