Question 1

When astronomers look out into the plane of the Milky Way Galaxy, how far can they see?

Accepted Answer

A)  infinitely far 
B)  about 200,000 ly 
C)  less than 1000 ly 
D)  about 24,000 ly 
A)  infinitely far 
B)  about 200,000 ly 
C)  less than 1000 ly 
D)  about 24,000 ly

Question 2

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

Accepted Answer

A)  the rotation curve of the Galaxy, in which orbital speeds of stars appear to obey Kepler's law. 
B)  the rotation curve of the Galaxy, in which orbital speeds of stars in the outer regions of the Galaxy are significantly higher than is predicted by Kepler's law in which the value for the observed mass in the Galaxy is used. 
C)  the unexpected absence of luminous matter (stars, and so on) beyond a certain distance from the galactic center. 
D)  the high amount of interstellar absorption in certain directions. 
A)  the rotation curve of the Galaxy, in which orbital speeds of stars appear to obey Kepler's law. 
B)  the rotation curve of the Galaxy, in which orbital speeds of stars in the outer regions of the Galaxy are significantly higher than is predicted by Kepler's law in which the value for the observed mass in the Galaxy is used. 
C)  the unexpected absence of luminous matter (stars, and so on) beyond a certain distance from the galactic center. 
D)  the high amount of interstellar absorption in certain directions.

Question 3

The 21-cm line is one of the most important wavelengths in radio astronomy. It is produced mainly in

Accepted Answer

A)  emission nebulae. 
B)  neutral hydrogen. 
C)  ionized hydrogen. 
D)  hot O and B stars. 
A)  emission nebulae. 
B)  neutral hydrogen. 
C)  ionized hydrogen. 
D)  hot O and B stars.

Question 4

A small galaxy orbits a larger one. After many orbits, the stars in the small galaxy have dispersed throughout the halo of the larger. This is an example of

Accepted Answer

A)  conservation of angular momentum. 
B)  galactic cannibalism. 
C)  globular cluster formation. 
D)  supermassive black hole formation. 
A)  conservation of angular momentum. 
B)  galactic cannibalism. 
C)  globular cluster formation. 
D)  supermassive black hole formation.

Question 5

How far away from Earth is the Andromeda Galaxy compared with the diameter of the Milky Way Galaxy?

Accepted Answer

A)  The Andromeda Galaxy is about 3 Milky Way diameters away. 
B)  The Andromeda Galaxy is about 20 Milky Way diameters away. 
C)  The Andromeda Galaxy is between 100 and 120 Milky Way diameters away. 
D)  The Andromeda Galaxy is several million Milky Way diameters away. 
A)  The Andromeda Galaxy is about 3 Milky Way diameters away. 
B)  The Andromeda Galaxy is about 20 Milky Way diameters away. 
C)  The Andromeda Galaxy is between 100 and 120 Milky Way diameters away. 
D)  The Andromeda Galaxy is several million Milky Way diameters away.

Question 6

A map of the Milky Way Galaxy deduced from radio observations of the 21-cm line emission from cool hydrogen gas and observations of spiral arm tracers such as giant molecular clouds reveals

Accepted Answer

A)  two spiral arms, one on each side of the Galaxy. 
B)  a smooth distribution of stars, characteristic of an elliptical galaxy. 
C)  at least four spiral arms. 
D)  one spiral arm that wraps around the Galaxy several times. 
A)  two spiral arms, one on each side of the Galaxy. 
B)  a smooth distribution of stars, characteristic of an elliptical galaxy. 
C)  at least four spiral arms. 
D)  one spiral arm that wraps around the Galaxy several times.

Question 7

What quantum transition occurs inside a hydrogen atom to produce a 21-cm radio photon?

Accepted Answer

A)  An electron falls from the level n = 100 to the level n = 99 in the atom. 
B)  An electron in the ground atomic state reverses its direction of spin with respect to that of the proton. 
C)  An electron reverses the direction of its motion in orbit around the proton. 
D)  The electron combines with the proton in the nucleus to become a neutron, producing energy. 
A)  An electron falls from the level n = 100 to the level n = 99 in the atom. 
B)  An electron in the ground atomic state reverses its direction of spin with respect to that of the proton. 
C)  An electron reverses the direction of its motion in orbit around the proton. 
D)  The electron combines with the proton in the nucleus to become a neutron, producing energy.

Question 8

If the Sun were to be at or close to the galactic center of the Milky Way, the intensity of starlight in the nighttime sky on Earth would be

Accepted Answer

A)  very much fainter than at present because neighboring stars would be obscured by dense dust and gas clouds. 
B)  about the same as it is now since neighboring stars would still be relatively far away. 
C)  about twice as bright as at present since neighboring stars would be mostly bright, young blue stars in about the same numbers as the present, older, and less bright red-giant neighbors to the Sun. 
D)  extremely intense from the dense field of stars, equivalent to about 200 full Moons. 
A)  very much fainter than at present because neighboring stars would be obscured by dense dust and gas clouds. 
B)  about the same as it is now since neighboring stars would still be relatively far away. 
C)  about twice as bright as at present since neighboring stars would be mostly bright, young blue stars in about the same numbers as the present, older, and less bright red-giant neighbors to the Sun. 
D)  extremely intense from the dense field of stars, equivalent to about 200 full Moons.

Question 9

The present estimate for the total mass of the Milky Way Galaxy in units of solar mass is about _____.

Accepted Answer

A)  2.3 * 108 
B)  1012 
C)  1.1 * 1011 
D)  1066 
A)  2.3 * 108 
B)  1012 
C)  1.1 * 1011 
D)  1066

Question 10

Interstellar matter obscures Earth's view of the disk of the Milky Way Galaxy

Accepted Answer

A)  most at radio wavelengths, where hydrogen absorbs radio waves efficiently, and least at optical wavelengths. 
B)  more at optical wavelengths and less or not at all at infrared and radio wavelengths. 
C)  very little at any wavelength. 
D)  more or less equally at all wavelengths, from radio waves to light waves. 
A)  most at radio wavelengths, where hydrogen absorbs radio waves efficiently, and least at optical wavelengths. 
B)  more at optical wavelengths and less or not at all at infrared and radio wavelengths. 
C)  very little at any wavelength. 
D)  more or less equally at all wavelengths, from radio waves to light waves.

Question 11

Which component of the Milky Way Galaxy accounts for interstellar extinction, the dimming of light from distant objects?

Accepted Answer

A)  cool hydrogen gas 
B)  so-called hidden or missing matter, since its absorbing properties render it invisible in the Galaxy 
C)  molecules such as H2 and CO, which are strong absorbers, in molecular clouds 
D)  dust 
A)  cool hydrogen gas 
B)  so-called hidden or missing matter, since its absorbing properties render it invisible in the Galaxy 
C)  molecules such as H2 and CO, which are strong absorbers, in molecular clouds 
D)  dust

Question 12

If interstellar dust obscures astronomers' view of distant regions of space at optical wavelengths, which of these statements is true?

Accepted Answer

A)  The obscuration is very clumpy and random over the whole sky; the individual absorbing dust clouds show no preference for one particular direction or plane. 
B)  The obscuration is roughly uniform over the whole sky. 
C)  The obscuration is the least in the plane of the Milky Way Galaxy and is strongest when one looks out into the galactic halo, at right angles in this plane. 
D)  The obscuration is severe only in the plane of the Milky Way Galaxy. 
A)  The obscuration is very clumpy and random over the whole sky; the individual absorbing dust clouds show no preference for one particular direction or plane. 
B)  The obscuration is roughly uniform over the whole sky. 
C)  The obscuration is the least in the plane of the Milky Way Galaxy and is strongest when one looks out into the galactic halo, at right angles in this plane. 
D)  The obscuration is severe only in the plane of the Milky Way Galaxy.

Question 13

Who won the Shapley-Curtis debate when it concluded in 1920?

Accepted Answer

A)  Shapley won. 
B)  Curtis won. 
C)  Both sides won in the sense that each successfully explained part of the data which were being debated. 
D)  Neither side won because there was no hard, reliable evidence to support either side. 
A)  Shapley won. 
B)  Curtis won. 
C)  Both sides won in the sense that each successfully explained part of the data which were being debated. 
D)  Neither side won because there was no hard, reliable evidence to support either side.

Question 14

What has microlensing told astronomers about the role of brown dwarfs in the Milky Way Galaxy?

Accepted Answer

A)  Brown dwarfs cannot be a major component of the dark matter in the Galaxy. 
B)  Brown dwarfs are a major component of the matter that is falling into the supermassive black hole in the galactic center. 
C)  Brown dwarfs are one of the most important components of the Galaxy's dark matter. 
D)  Microlensing has stated almost nothing yet about brown dwarfs-microlensing is too difficult to observe. 
A)  Brown dwarfs cannot be a major component of the dark matter in the Galaxy. 
B)  Brown dwarfs are a major component of the matter that is falling into the supermassive black hole in the galactic center. 
C)  Brown dwarfs are one of the most important components of the Galaxy's dark matter. 
D)  Microlensing has stated almost nothing yet about brown dwarfs-microlensing is too difficult to observe.

Question 15

Positrons (positively charged electrons) are being produced in the galactic center of the Milky Way. How have the positrons been detected?

Accepted Answer

A)  The positrons create arches of magnetic field that are visible at radio wavelengths. 
B)  The positrons spiral in magnetic fields, producing a strong source of synchrotron radiation. 
C)  The positrons annihilate with ordinary electrons, producing gamma rays with a characteristic energy. 
D)  The positrons reach Earth as cosmic rays from the direction of the galactic center. 
A)  The positrons create arches of magnetic field that are visible at radio wavelengths. 
B)  The positrons spiral in magnetic fields, producing a strong source of synchrotron radiation. 
C)  The positrons annihilate with ordinary electrons, producing gamma rays with a characteristic energy. 
D)  The positrons reach Earth as cosmic rays from the direction of the galactic center.

Question 16

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

Accepted Answer

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

Question 17

A classical Cepheid variable star in a distant galaxy has an apparent magnitude of +20.3. By measuring its period and using the period-luminosity relation, its absolute magnitude is -6.0. Assuming that there is no interstellar absorption, what is the distance to the galaxy in parsecs?

Accepted Answer

A)  3.6 * 104 pc 
B)  7.2 * 103 pc 
C)  1.1 * 105 pc 
D)  1.8 * 106 pc 
A)  3.6 * 104 pc 
B)  7.2 * 103 pc 
C)  1.1 * 105 pc 
D)  1.8 * 106 pc

Question 18

What is the significance of the object Sagittarius A* ("Sagittarius A-star") in the Milky Way Galaxy?

Accepted Answer

A)  Sagittarius A* appears to be a jet of material ejected from an accretion disk around a supermassive black hole in the galactic nucleus. 
B)  Sagittarius A* is a globular cluster passing close to the galactic nucleus, and the RR Lyrae stars in it allow the distance to the galactic center to be calculated. 
C)  Sagittarius A* is a bright, high-speed cloud of gas close to the galactic nucleus that allows the mass of the nucleus to be calculated. 
D)  Sagittarius A* appears to be the actual nucleus of the Galaxy. 
A)  Sagittarius A* appears to be a jet of material ejected from an accretion disk around a supermassive black hole in the galactic nucleus. 
B)  Sagittarius A* is a globular cluster passing close to the galactic nucleus, and the RR Lyrae stars in it allow the distance to the galactic center to be calculated. 
C)  Sagittarius A* is a bright, high-speed cloud of gas close to the galactic nucleus that allows the mass of the nucleus to be calculated. 
D)  Sagittarius A* appears to be the actual nucleus of the Galaxy.

Question 19

A radio astronomer points a radio telescope through the Milky Way's disk in a direction directly away from the center of the Galaxy. If the astronomer measures the Doppler shift of the 21-cm radio line of hydrogen from interstellar clouds at several different distances from the Sun along this line of sight, what should be the result? Refer to Figure 16-8 from the text.

Accepted Answer

A)  The Doppler shift should have a constant value, regardless of distance, as a result of the Sun's speed of motion around the center of the Galaxy. 
B)  The Doppler shift should be almost zero for all clouds, regardless of distance. 
C)  The Doppler shift should rise to a maximum at some distance, then decrease again. 
D)  The Doppler shift should be larger the farther away the cloud is. 
A)  The Doppler shift should have a constant value, regardless of distance, as a result of the Sun's speed of motion around the center of the Galaxy. 
B)  The Doppler shift should be almost zero for all clouds, regardless of distance. 
C)  The Doppler shift should rise to a maximum at some distance, then decrease again. 
D)  The Doppler shift should be larger the farther away the cloud is.

Question 20

The luminosity of a Cepheid variable star compared with that of the Sun is

Accepted Answer

A)  generally between 10 and 100 times larger. 
B)  about the same. 
C)  significantly less. 
D)  several hundred to several thousand times larger. 
A)  generally between 10 and 100 times larger. 
B)  about the same. 
C)  significantly less. 
D)  several hundred to several thousand times larger.

When astronomers look out into the plane of the Milky Way Galaxy, how far can they see?

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

The 21-cm line is one of the most important wavelengths in radio astronomy. It is produced mainly in

A small galaxy orbits a larger one. After many orbits, the stars in the small galaxy have dispersed throughout the halo of the larger. This is an example of

How far away from Earth is the Andromeda Galaxy compared with the diameter of the Milky Way Galaxy?

A map of the Milky Way Galaxy deduced from radio observations of the 21-cm line emission from cool hydrogen gas and observations of spiral arm tracers such as giant molecular clouds reveals

What quantum transition occurs inside a hydrogen atom to produce a 21-cm radio photon?

If the Sun were to be at or close to the galactic center of the Milky Way, the intensity of starlight in the nighttime sky on Earth would be

The present estimate for the total mass of the Milky Way Galaxy in units of solar mass is about _____.

Interstellar matter obscures Earth's view of the disk of the Milky Way Galaxy

Which component of the Milky Way Galaxy accounts for interstellar extinction, the dimming of light from distant objects?

If interstellar dust obscures astronomers' view of distant regions of space at optical wavelengths, which of these statements is true?

Who won the Shapley-Curtis debate when it concluded in 1920?

What has microlensing told astronomers about the role of brown dwarfs in the Milky Way Galaxy?

Positrons (positively charged electrons) are being produced in the galactic center of the Milky Way. How have the positrons been detected?

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

A classical Cepheid variable star in a distant galaxy has an apparent magnitude of +20.3. By measuring its period and using the period-luminosity relation, its absolute magnitude is -6.0. Assuming that there is no interstellar absorption, what is the distance to the galaxy in parsecs?

What is the significance of the object Sagittarius A* ("Sagittarius A-star") in the Milky Way Galaxy?

The luminosity of a Cepheid variable star compared with that of the Sun is

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Lives of Stars From Birth Through Middle Age

The Death of Stars

Black Holes: Matters of Gravity

Galaxies

Quasars and Other Active Galaxies

Cosmology

Astrobiology

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Exam 16: The Milky Way Galaxy

When astronomers look out into the plane of the Milky Way Galaxy, how far can they see?

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

The 21-cm line is one of the most important wavelengths in radio astronomy. It is produced mainly in

A small galaxy orbits a larger one. After many orbits, the stars in the small galaxy have dispersed throughout the halo of the larger. This is an example of

How far away from Earth is the Andromeda Galaxy compared with the diameter of the Milky Way Galaxy?

A map of the Milky Way Galaxy deduced from radio observations of the 21-cm line emission from cool hydrogen gas and observations of spiral arm tracers such as giant molecular clouds reveals

What quantum transition occurs inside a hydrogen atom to produce a 21-cm radio photon?

If the Sun were to be at or close to the galactic center of the Milky Way, the intensity of starlight in the nighttime sky on Earth would be

The present estimate for the total mass of the Milky Way Galaxy in units of solar mass is about _____.

Interstellar matter obscures Earth's view of the disk of the Milky Way Galaxy

Which component of the Milky Way Galaxy accounts for interstellar extinction, the dimming of light from distant objects?

If interstellar dust obscures astronomers' view of distant regions of space at optical wavelengths, which of these statements is true?

Who won the Shapley-Curtis debate when it concluded in 1920?

What has microlensing told astronomers about the role of brown dwarfs in the Milky Way Galaxy?

Positrons (positively charged electrons) are being produced in the galactic center of the Milky Way. How have the positrons been detected?

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

A classical Cepheid variable star in a distant galaxy has an apparent magnitude of +20.3. By measuring its period and using the period-luminosity relation, its absolute magnitude is -6.0. Assuming that there is no interstellar absorption, what is the distance to the galaxy in parsecs?

What is the significance of the object Sagittarius A* ("Sagittarius A-star") in the Milky Way Galaxy?

The luminosity of a Cepheid variable star compared with that of the Sun is

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Lives of Stars From Birth Through Middle Age

The Death of Stars

Black Holes: Matters of Gravity

Galaxies

Quasars and Other Active Galaxies

Cosmology

Astrobiology

Filters