Question 1

What do astronomers know about the geometry of the dark matter distribution in the vicinity of the Milky Way Galaxy?

Accepted Answer

A)  The dark matter appears to be a lens-shaped disk like the Galaxy's disk of visible stars, only larger. 
B)  The dark matter appears to be a spherical halo. 
C)  Dark matter, including that near the Milky Way Galaxy, appears to be part of a uniform density distribution that fills all space. 
D)  The geometry of the dark matter distribution, like its constituents, is totally unknown at the present time. 
A)  The dark matter appears to be a lens-shaped disk like the Galaxy's disk of visible stars, only larger. 
B)  The dark matter appears to be a spherical halo. 
C)  Dark matter, including that near the Milky Way Galaxy, appears to be part of a uniform density distribution that fills all space. 
D)  The geometry of the dark matter distribution, like its constituents, is totally unknown at the present time. B

Question 2

The supermassive black hole at the center of the Milky Way Galaxy is believed to be 4.3 * 106 solar masses. What is its diameter in light-years?

Accepted Answer

A)  1.3 * 10-6 
B)  2.6 * 10-6 
C)  1.3 *107 
D)  2.6 * 107 
A)  1.3 * 10-6 
B)  2.6 * 10-6 
C)  1.3 *107 
D)  2.6 * 107 B

Question 3

The positrons near the galactic center can be detected because they annihilate with electrons and emit gamma rays. Two gamma rays are produced in such a situation to conserve both energy and momentum. Suppose the positron and electron, each with energy mc2, convert all of this energy into two identical gamma-ray photons. What will be the wavelength of these photons? The mass of an electron is 9.1 * 10-31 kg.

Accepted Answer

A)  1.5 * 10-2 nm 
B)  2.4 * 10-3 nm 
C)  3.9* 10-4 nm 
D)  7.9 *10-5 nm 
A)  1.5 * 10-2 nm 
B)  2.4 * 10-3 nm 
C)  3.9* 10-4 nm 
D)  7.9 *10-5 nm B

Question 4

Suppose one could examine a star and determine its absolute magnitude M without any intervening gas and dust. Compared to its absolute magnitude measured with gas and dust between Earth and the star, this "clean" measurement of M would be

Accepted Answer

A)  a larger number. 
B)  a smaller number. 
C)  the same number. 
D)  either larger or smaller depending on the star's speed (toward or away). 
A)  a larger number. 
B)  a smaller number. 
C)  the same number. 
D)  either larger or smaller depending on the star's speed (toward or away).

Question 5

An astronomer finds a very old astronomy book, in which the Messier object M31 is referred to as the Andromeda Nebula. The astronomer might suspect that this book was written BEFORE

Accepted Answer

A)  1780. 
B)  1845. 
C)  1924. 
D)  1954. 
A)  1780. 
B)  1845. 
C)  1924. 
D)  1954.

Question 6

What is the motion of stars in the bulge across the inner part of the Milky Way Galaxy?

Accepted Answer

A)  The stars move in roughly circular orbits. 
B)  The stars oscillate back and forth across the bulge, retracing the same path again and again. 
C)  The stars are part of a density wave that moves around the galactic center. 
D)  The stars basically remain stationary within the bulge. 
A)  The stars move in roughly circular orbits. 
B)  The stars oscillate back and forth across the bulge, retracing the same path again and again. 
C)  The stars are part of a density wave that moves around the galactic center. 
D)  The stars basically remain stationary within the bulge.

Question 7

The twentieth century opened with a major unresolved question among astronomers. This was the subject of the famous Shapley-Curtis debate. What was this question?

Accepted Answer

A)  How old is the Milky Way Galaxy? 
B)  What is the nature of dark matter? 
C)  Is general relativity true? 
D)  Is the Milky Way Galaxy the whole universe, or only one of many galaxies? 
A)  How old is the Milky Way Galaxy? 
B)  What is the nature of dark matter? 
C)  Is general relativity true? 
D)  Is the Milky Way Galaxy the whole universe, or only one of many galaxies?

Question 8

What is a galactic halo?

Accepted Answer

A)  system of arcs and other gas clouds surrounding a galactic nucleus 
B)  system of satellite galaxies surrounding the Milky Way Galaxy 
C)  spherical distribution of stars and globular clusters centered on a nuclear bulge 
D)  large disk of stars and molecular clouds extending outward from a nuclear bulge 
A)  system of arcs and other gas clouds surrounding a galactic nucleus 
B)  system of satellite galaxies surrounding the Milky Way Galaxy 
C)  spherical distribution of stars and globular clusters centered on a nuclear bulge 
D)  large disk of stars and molecular clouds extending outward from a nuclear bulge

Question 9

What happens when the electron in a hydrogen atom flips its direction of spin from parallel to antiparallel to that of the proton?

Accepted Answer

A)  Nothing. This event is a forbidden transition that never occurs. 
B)  The atom emits a photon of 656.3-nm wavelength (H $\alpha$ ) in the red region of the spectrum. 
C)  The atom emits a photon of 21-cm wavelength in the radio region of the spectrum. 
D)  The atom emits a photon of 121.5-nm wavelength (L $\alpha$ ) in the UV region of the spectrum. 
A)  Nothing. This event is a forbidden transition that never occurs. 
B)  The atom emits a photon of 656.3-nm wavelength (H $\alpha$ ) in the red region of the spectrum. 
C)  The atom emits a photon of 21-cm wavelength in the radio region of the spectrum. 
D)  The atom emits a photon of 121.5-nm wavelength (L $\alpha$ ) in the UV region of the spectrum.

Question 10

Where is the solar system located in the Milky Way Galaxy?

Accepted Answer

A)  in the galactic disk 
B)  The solar system is not in a galaxy but in the intergalactic space between galaxies. 
C)  in the galactic halo 
D)  in the galactic nucleus 
A)  in the galactic disk 
B)  The solar system is not in a galaxy but in the intergalactic space between galaxies. 
C)  in the galactic halo 
D)  in the galactic nucleus

Question 11

Which of these accurately describes the characteristics of the object at the center of the Milky Way Galaxy?

Accepted Answer

A)  20 solar masses in a volume the size of the Sun 
B)  several trillion solar masses in a volume 2 ly in diameter 
C)  4 million solar masses in a volume smaller than Earth's orbit 
D)  5 billion solar masses in a volume smaller then Jupiter's orbit 
A)  20 solar masses in a volume the size of the Sun 
B)  several trillion solar masses in a volume 2 ly in diameter 
C)  4 million solar masses in a volume smaller than Earth's orbit 
D)  5 billion solar masses in a volume smaller then Jupiter's orbit

Question 12

The observational fact about a Cepheid variable star that leads to a measurement of its distance from Earth is that its period of variation is directly related to its

Accepted Answer

A)  surface temperature. 
B)  position along the spiral arms of a galaxy. 
C)  apparent magnitude. 
D)  absolute magnitude. 
A)  surface temperature. 
B)  position along the spiral arms of a galaxy. 
C)  apparent magnitude. 
D)  absolute magnitude.

Question 13

If the black hole in the center of the Milky Way Galaxy were 4 *106 solar masses, what would be the orbital period of Earth around this object in an orbit of radius 1 au (assuming that Newtonian physics and Kepler's third law apply)?

Accepted Answer

A)  less than 1 second 
B)  3 minutes 
C)  4 $1 / 2$ hours 
D)  5 weeks 
A)  less than 1 second 
B)  3 minutes 
C)  4 $1 / 2$ hours 
D)  5 weeks

Question 14

When astronomers measure the narrow line emissions of hydrogen at 21-cm radio wavelengths along a particular line of sight through the disk of the Milky Way Galaxy, they can tell the distances to different hydrogen clouds because

Accepted Answer

A)  absorption of extragalactic radiation at this wavelength is greater the farther away the absorber is from the Sun. 
B)  clouds that are farther away have smaller angular sizes. 
C)  the emission is weaker from clouds that are farther away. 
D)  clouds at different distances have different Doppler shifts because of the rotation of the Galaxy. 
A)  absorption of extragalactic radiation at this wavelength is greater the farther away the absorber is from the Sun. 
B)  clouds that are farther away have smaller angular sizes. 
C)  the emission is weaker from clouds that are farther away. 
D)  clouds at different distances have different Doppler shifts because of the rotation of the Galaxy.

Question 15

Suppose a spiral galaxy is a million parsecs away so that its distance modulus is 25. What would be the approximate luminosity of an RR Lyrae variable star in this galaxy?

Accepted Answer

A)  25 LSun 
B)  100 LSun 
C)  2500 LSun 
D)  The luminosity cannot be determined from this information alone. 
A)  25 LSun 
B)  100 LSun 
C)  2500 LSun 
D)  The luminosity cannot be determined from this information alone.

Question 16

The Milky Way is an example of which type of galaxy?

Accepted Answer

A)  spiral 
B)  irregular 
C)  lenticular, S0 type 
D)  elliptical 
A)  spiral 
B)  irregular 
C)  lenticular, S0 type 
D)  elliptical

Question 17

The stellar components of the Milky Way Galaxy that act as tracers for the mapping of the spiral arm structure in the Galaxy are

Accepted Answer

A)  bright Population I stars and emission nebulae surrounding them. 
B)  globular clusters. 
C)  supernova explosions, because they are very luminous and can be seen through considerable dust and gas. 
D)  old, red giant stars and white dwarfs. 
A)  bright Population I stars and emission nebulae surrounding them. 
B)  globular clusters. 
C)  supernova explosions, because they are very luminous and can be seen through considerable dust and gas. 
D)  old, red giant stars and white dwarfs.

Question 18

In 1785, William Herschel proposed that the solar system was at the center of the Milky Way Galaxy. How did he reach this conclusion?

Accepted Answer

A)  Like the ancient Greeks and many of their successors for over a thousand years, Herschel based his conclusion on the philosophical importance of Earth in the cosmos. 
B)  Herschel's observations suggested that the stars in the Milky Way Galaxy were distributed uniformly around Earth. 
C)  Herschel measured distances to globular clusters and determined that they were distributed uniformly around Earth. 
D)  Herschel determined that Cepheid variable stars in the Milky Way Galaxy were distributed uniformly around Earth. 
A)  Like the ancient Greeks and many of their successors for over a thousand years, Herschel based his conclusion on the philosophical importance of Earth in the cosmos. 
B)  Herschel's observations suggested that the stars in the Milky Way Galaxy were distributed uniformly around Earth. 
C)  Herschel measured distances to globular clusters and determined that they were distributed uniformly around Earth. 
D)  Herschel determined that Cepheid variable stars in the Milky Way Galaxy were distributed uniformly around Earth.

Question 19

What is the source of the Milky Way's global magnetic field?

Accepted Answer

A)  supernova explosions 
B)  the supermassive black hole at the center of the Galaxy 
C)  mergers with other galaxies 
D)  The magnetic field's origin is not yet well-understood. 
A)  supernova explosions 
B)  the supermassive black hole at the center of the Galaxy 
C)  mergers with other galaxies 
D)  The magnetic field's origin is not yet well-understood.

Question 20

Which of these components of the Milky Way Galaxy outlines the spiral arms of the Galaxy?

Accepted Answer

A)  young O and B stars, dust, and gas 
B)  globular clusters 
C)  predominantly solar-type stars 
D)  white dwarf stars 
A)  young O and B stars, dust, and gas 
B)  globular clusters 
C)  predominantly solar-type stars 
D)  white dwarf stars

What do astronomers know about the geometry of the dark matter distribution in the vicinity of the Milky Way Galaxy?

The supermassive black hole at the center of the Milky Way Galaxy is believed to be 4.3 * 10⁶ solar masses. What is its diameter in light-years?

Suppose one could examine a star and determine its absolute magnitude M without any intervening gas and dust. Compared to its absolute magnitude measured with gas and dust between Earth and the star, this "clean" measurement of M would be

An astronomer finds a very old astronomy book, in which the Messier object M31 is referred to as the Andromeda Nebula. The astronomer might suspect that this book was written BEFORE

What is the motion of stars in the bulge across the inner part of the Milky Way Galaxy?

The twentieth century opened with a major unresolved question among astronomers. This was the subject of the famous Shapley-Curtis debate. What was this question?

What is a galactic halo?

What happens when the electron in a hydrogen atom flips its direction of spin from parallel to antiparallel to that of the proton?

Where is the solar system located in the Milky Way Galaxy?

Which of these accurately describes the characteristics of the object at the center of the Milky Way Galaxy?

The observational fact about a Cepheid variable star that leads to a measurement of its distance from Earth is that its period of variation is directly related to its

If the black hole in the center of the Milky Way Galaxy were 4 *10⁶ solar masses, what would be the orbital period of Earth around this object in an orbit of radius 1 au (assuming that Newtonian physics and Kepler's third law apply)?

When astronomers measure the narrow line emissions of hydrogen at 21-cm radio wavelengths along a particular line of sight through the disk of the Milky Way Galaxy, they can tell the distances to different hydrogen clouds because

Suppose a spiral galaxy is a million parsecs away so that its distance modulus is 25. What would be the approximate luminosity of an RR Lyrae variable star in this galaxy?

The Milky Way is an example of which type of galaxy?

The stellar components of the Milky Way Galaxy that act as tracers for the mapping of the spiral arm structure in the Galaxy are

In 1785, William Herschel proposed that the solar system was at the center of the Milky Way Galaxy. How did he reach this conclusion?

What is the source of the Milky Way's global magnetic field?

Which of these components of the Milky Way Galaxy outlines the spiral arms of the Galaxy?

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

Exam 16: The Milky Way Galaxy

What do astronomers know about the geometry of the dark matter distribution in the vicinity of the Milky Way Galaxy?

The supermassive black hole at the center of the Milky Way Galaxy is believed to be 4.3 * 106 solar masses. What is its diameter in light-years?

Suppose one could examine a star and determine its absolute magnitude M without any intervening gas and dust. Compared to its absolute magnitude measured with gas and dust between Earth and the star, this "clean" measurement of M would be

An astronomer finds a very old astronomy book, in which the Messier object M31 is referred to as the Andromeda Nebula. The astronomer might suspect that this book was written BEFORE

What is the motion of stars in the bulge across the inner part of the Milky Way Galaxy?

The twentieth century opened with a major unresolved question among astronomers. This was the subject of the famous Shapley-Curtis debate. What was this question?

What is a galactic halo?

What happens when the electron in a hydrogen atom flips its direction of spin from parallel to antiparallel to that of the proton?

Where is the solar system located in the Milky Way Galaxy?

Which of these accurately describes the characteristics of the object at the center of the Milky Way Galaxy?

The observational fact about a Cepheid variable star that leads to a measurement of its distance from Earth is that its period of variation is directly related to its

If the black hole in the center of the Milky Way Galaxy were 4 *106 solar masses, what would be the orbital period of Earth around this object in an orbit of radius 1 au (assuming that Newtonian physics and Kepler's third law apply)?

When astronomers measure the narrow line emissions of hydrogen at 21-cm radio wavelengths along a particular line of sight through the disk of the Milky Way Galaxy, they can tell the distances to different hydrogen clouds because

Suppose a spiral galaxy is a million parsecs away so that its distance modulus is 25. What would be the approximate luminosity of an RR Lyrae variable star in this galaxy?

The Milky Way is an example of which type of galaxy?

The stellar components of the Milky Way Galaxy that act as tracers for the mapping of the spiral arm structure in the Galaxy are

In 1785, William Herschel proposed that the solar system was at the center of the Milky Way Galaxy. How did he reach this conclusion?

What is the source of the Milky Way's global magnetic field?

Which of these components of the Milky Way Galaxy outlines the spiral arms of the Galaxy?

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

The supermassive black hole at the center of the Milky Way Galaxy is believed to be 4.3 * 10⁶ solar masses. What is its diameter in light-years?

If the black hole in the center of the Milky Way Galaxy were 4 *10⁶ solar masses, what would be the orbital period of Earth around this object in an orbit of radius 1 au (assuming that Newtonian physics and Kepler's third law apply)?