Why is iron significant to understanding how a supernova occurs?
answer
Iron cannot release energy either by fission or fusion.
question
Where does gold (the element) come from?
answer
It is produced during the supernova explosions of high-mass stars.
question
Which two processes can generate energy to help a star maintain its internal thermal pressure?
answer
Nuclear fusion and gravitational contraction.
question
Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?
answer
The cloud must radiate much of its thermal energy.
question
Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?
answer
A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
question
Carbon fusion occur in high-mass stars but not in low-mass stars because
answer
The cores of low-mass stars never get hot enough for carbon fusion
question
After a supernova explosion, the remains of the stellar core
answer
may be either a neutron star or a black hole.
question
Why is supernova 1987 A particularly important to astronomers?
answer
It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes.
question
Suppose the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?
answer
Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.
question
A spinning neutron star has been observed at the center of a
answer
supernova remnant.
question
Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?
answer
Planetary nebula formation is more common.
question
A typical white dwarf is
answer
as massive as the sun but only about as large in size as Earth
question
The maximum mass of a white dwarf is
answer
about 1.4 times the mass of our sun.
question
Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass unit?
answer
The white dwarf will explode completely as a white dwarf supernova.
question
A neutron star is
answer
The remains of a star that died in a massive star supernova (if no black hole was created).
question
Which of the following is NOT a general characteristic of the four Jovian planets in our solar system?
answer
They are higher in average density than are the terrestrial planets.
question
Overall, Jupiter's composition is most like that of
answer
The Sun
question
How do typical wind speeds in Jupiter's atmosphere compare to typical wind speeds on Earth?
answer
They are much faster than hurricane winds on earth.
question
What is the Great Red Spot?
answer
a long-lived, high-pressure storm on Jupiter.
question
Which statement about Io is true?
answer
It is the most volcanically active body in our solar system.
question
Which moon has a thick atmosphere made mostly of nitrogen?
answer
Titan
question
Which moon is considered likely to have a deep, subsurface ocean of liquid water?
answer
Europa
question
Suppose you could float in space just a few meters above Saturn's rings. What would you see as you looked down on the rings?
answer
Countless icy particles, ranging in size from dust grains to large boulders.
question
Which of the following statements best describes the size of the largest asteroid, Ceres?
answer
It is a little less than half the diameter of our moon.
question
If we could put all the asteroids together, their total mass would be
answer
much less than the mass of any terrestrial planet
question
Why didn't a planet form where the asteroid belt is now located?
answer
Gravitational tugs from Jupiter prevented material from collecting together to form a planet.
question
When you see the bright flash of a meteor, what are you actually seeing?
answer
The glow from a pea-size particle and the surrounding air as the particle burns up in our atmosphere.
question
Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different?
answer
It would have only one tail instead of two.
question
When we see a meteor shower, it means that
answer
earth is crossing the orbit of a comet
question
What is Pluto's moon Charon thought to have in common with our own moon?
answer
It probably formed as a result of a giant impact.
question
According to modern science, approximately how old is the sun?
answer
4 1/2 billion years
question
The sun will exhaust its nuclear fuel in about
answer
5 billion years
question
Which of the following correctly describes how the process of gravitational contraction can make a star hot?
answer
When a star contracts in size, gravitational potential energy is converted to thermal energy.
question
What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?
answer
Gravitational foce and outward pressure.
question
The source of energy that keeps the Sun shining today is
answer
Nuclear fusion
question
When we say that the sun is a ball of plasma, we mean that
answer
The sun consists of gas in which many or most of the atoms are ionized (missing electrons).
question
What is the Sun made of (by mass)?
answer
70% hydrogen, 28% helium, 2% other elements.
question
The sun's average surface (photosphere) temperature is about
answer
5,800 K
question
The total amount of power (in watts, for example) that a star radiates into space is called its
answer
Luminosity
question
According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?
answer
Its apparent brightness will DECREASE by a factor of 9.
question
If Star A is closer to us than Star B, then Star A's PARALLAX angle is
answer
larger than that of Star B
question
From hottest to coolest, the order of the spectral types of stars is
answer
OBAFGKM
question
Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?
answer
The star is a member of a binary star system.
question
The axes on a Hertzsprung-Russell (H-R) diagram represent
answer
luminosity and surface temperature
question
How is the lifetime of a star related to its mass?
answer
More massive stars live much shorter lives than less massive stars.
question
All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?
answer
its mass and its stage of life.
question
Star A is identical to Star B, excepts that Star A is twice as far from us as Star B. Therefore:
answer
Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.
question
A star with a parallax angle of 1/20 arc second is
answer
20 parsecs away
question
Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude?
answer
Rigel has a higher surface temperature than Sirius.
question
To calculate the masses of stars in a binary system, we must measure their
answer
orbital period and average orbital distance.
question
You observe a star and you want to plot it on an H-R diagram. You will need to know all of the following, except the star's
answer
Mass.
question
The total amount of power (in watts, for example) that a star radiates into space is its
answer
luminosity.
question
Ten parsecs is about
answer
32.6 light years
question
Our sun is a star of spectral type
answer
G
question
How is the lifetime of a star related to its mass?
answer
More massive stars live much shorter lives than less massive stars.
question
What is the common trait of all main sequence stars?
answer
They generate energy through hydrogen fusion in their core.
question
Our sun is considered to be a
answer
low-mass star
question
Where would a brown dwarf be located on an H-R diagram?
answer
Below and to the right of the lowest part of the main sequence.
question
How does the interstellar medium affect our view of most of the galaxy?
answer
It prevents us from seeing most of the galactic disk with visible and ultraviolet light.
question
How does the diameter of the disk of the Milky Way Galaxy compare to its thickness?
answer
The diameter is about 100 times as great as the thickness.
question
What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy?
answer
The galaxy's bulge
question
The sun's location in the Milky Way Galaxy is
answer
In the galactic disk, roughly halfway between the center and the outer edge of the disk.
question
What do we mean by the interstellar medium?
answer
the gas and dust that lies in between the stars in the Milky Way.
question
How do disk stars orbit the center of the galaxy?
answer
They all orbit in roughly the same plane and in the same direction.
question
How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path?
answer
by applying Newton's version of Kepler's third law to the orbits of the Sun or other nearby stars around the center of the galaxy.
question
What do we mean by the star-gas-star cycle?
answer
It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.
question
The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with
answer
radio telescopes observing at a wavelength of 21 centimeters.
question
Most stars in the Milky Way's halo are
answer
very old.
question
What do halo stars do differently from disk stars?
answer
They orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.
question
Where does most star formation occur in the Milky Way Galaxy?
answer
In the spiral arms.
question
Based on observations, which of the following statements about stars in the Milky Way is generally true?
answer
The older the star, the lower its abundance of heavy elements.
question
How would you expect a star that formed recently in the disk of the galaxy to differ from one that formed early in the history of the disk?
answer
It should have a higher fraction of elements heavier than hydrogen and helium.
question
The most common form of gas in the disk of the Milky Way Galaxy is
answer
atomic hydrogen gas.
question
Over time, the star-gas-star cycle leads the gas in the Milky Way to
answer
have a greater abundance of heavy elements.
question
If you could watch a time-lapse movie of the interstellar medium over hundreds of millions of years, what would you see?
answer
Gas that is often moving at high speed, particularly after one or more supernovae, and constantly changing form between molecular clouds, atomic hydrogen, and hot, ionized bubbles and super bubbles.
question
Why do we believe that most of the Milky Way is in the form of dark matter?
answer
The orbital speeds of stars far from the galactic center are surprisingly high.
question
Spiral arms appear bright because
answer
they contain more hot young stars than other parts of the disk.
question
What is the best evidence for an extremely massive black hole in the center of the Milky Way?
answer
The orbits of stars in the center of the galaxy indicate that the presence of 3 to 4 million solar mass object in a region no larger than our solar system.
question
The reason that small planets tend to lose interior heat faster than larger planets is essential the same reason that
answer
a large baked potato takes longer to cool than a small baked potato.
question
What would happen to Jupiter if we could somehow double its mass?
answer
Its density would increase but its diameter would barely change.
question
What do asteroids and comets have in common?
answer
Most are unchanged since their formation in the solar nebula
question
An icy leftover planetesimal orbiting the sun is
answer
a comet.
question
Why do asteroids and comets differ in composition?
answer
Asteroids formed inside the frost line, while comets formed outside.
question
Which of the following best describes why the sun emits most of its energy in the form of visible light?
answer
Like all objects, the sun emits thermal radiation with a spectrum that depends on its temperature, and the sun's surface temperature is just right for emitting mostly visible light.
question
The source of energy that keeps the sun shining today is
answer
nuclear fusion.
question
What is a protostar?
answer
A star that is still in the process of forming.
question
What kind of gas cloud is most likely to give birth to stars?
answer
A cold, dense gas cloud.
question
Pulsars are thought to be
answer
rapidly rotating neutron stars.
question
Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?
answer
Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.
question
Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on) in a high mass star is NOT true?
answer
Each successive stage creates an element with a higher atomic number and atomic mass number.
question
Which event marks the beginning of a supernova?
answer
The sudden collapse of an iron into a compact ball of neutrons.
question
Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?
answer
We can learn the distance to the galaxy.
question
In 1924, Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way, thus putting to rest the idea that it might have been a cloud within our own galaxy. How was he able to prove this?
answer
He observed individual Cepheid variable stars in Andromeda and applied the period-luminosity relation.
question
Why are white dwarf supernovae more useful than massive star supernovae for measuring cosmic distances?
answer
White dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak luminosities.
question
What does cosmological redshift do to light?
answer
Stretches its wavelength
question
A quasar's spectrum is hugely redshifted. What do most astronomers think this large redshift tells us about the quasar?
answer
The distance to the quasar.
question
Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?
answer
Active galactic nuclei tend to become less active as they age.
question
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
answer
The X-ray source is no more than a few light-days in diameter.
question
Why do we call dark matter "dark"?
answer
It emits no radiation that we have been able to detect.
question
Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did NOT contain dark matter. How would their rotation curves be different?
answer
The orbital speeds would fall off sharply with increasing distance from the galactic center.
question
The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they tell us anything about where the dark matter is located within the galaxy?
answer
Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center.
question
Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster?
answer
The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass.
question
Is space expanding within clusters of galaxies?
answer
NO, because their gravity is strong enough to hold them together even while the universe as a whole expands.
question
Which of the following statements about large-scale structure is probably NOT true?
answer
Clusters and superclusters appear to be randomly scattered about the universe, like dots sprinkled randomly on a wall.
question
Based on current evidence, how does the actual average density of matter in the universe compare to the critical density?
answer
The actual density, even with dark matter included, is less than about a third of the critical density.
question
Which of the following statements best describes the current state of understanding regarding the apparent acceleration of the expansion of the universe?
answer
We have moderately strong evidence that the acceleration is real, but essentially no idea what is causing it.
question
Which of the following best summarizes what we mean by dark energy?
answer
It is a name given to whatever is causing the expansion of the universe to accelerate with time.
question
The text states that luminous matter in the Milky Way seems to be much like the tip of an ice berg. This refers to the idea that...
answer
dark matter represents much more mass and extends much farther from the galactic center than the visible stars of the Milky Way.
question
When we say that a cluster of galaxies is acting as a gravitational lens, what do we mean?
answer
It bends or distorts the light coming from galaxies located behind it.
question
What do we mean when we say that particles such as neutrinos or WIMPS are weakly interacting?
answer
They respond to the weak force but not to the electromagnetic force, which means they cannot emit light.
question
The critical density of the universe is the
answer
Average density the universe would need for gravity to someday halt the current expansion if dark energy did not exist.
question
What is the primary form of evidence that has led astronomers to conclude that the expansion of the universe is accelerating?
answer
Observations of WHITE DWARF SUPERNOVAE.
question
How do we determine the conditions that existed in the very early universe?
answer
We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.
question
What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?
answer
The basic chemical composition of the universe had been determined.
question
Which of the following is NOT an observed characteristic of the cosmic microwave background?
answer
It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.
question
In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why?
answer
Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.
question
Based on the results from the WMAP satellite, the overall composition of the universe is...
answer
4% ordinary (baryonic matter, 23% nonbaryonic dark matter, 73% dark energy.
question
Which of the following best describes the predominant scientific view of the origin of life on Earth?
answer
We may never know precisely how life arose, but current evidence suggests that life probably can arise naturally under the conditions that prevailed on the early earth.
question
When we analyze whether a world is a possible home to life, they key thing we look for is
answer
The past or present existence of liquid water.
question
In general, how does the size and location of a star's habitable zone depend on the star's mass?
answer
The smaller (less massive) the star, the smaller and the closer-in the habitable zone.
question
We are not yet capable of detecting life on planets around other stars. But as our technology develops, our first real chance of detecting such life will probably come from
answer
examining spectral lines from the atmosphere of distant planets.
Why is iron significant to understanding how a supernova occurs?
answer
Iron cannot release energy either by fission or fusion.
question
Where does gold (the element) come from?
answer
It is produced during the supernova explosions of high-mass stars.
question
Which two processes can generate energy to help a star maintain its internal thermal pressure?
answer
Nuclear fusion and gravitational contraction.
question
Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?
answer
The cloud must radiate much of its thermal energy.
question
Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?
answer
A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
question
Carbon fusion occur in high-mass stars but not in low-mass stars because
answer
The cores of low-mass stars never get hot enough for carbon fusion
question
After a supernova explosion, the remains of the stellar core
answer
may be either a neutron star or a black hole.
question
Why is supernova 1987 A particularly important to astronomers?
answer
It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes.
question
Suppose the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?
answer
Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.
question
A spinning neutron star has been observed at the center of a
answer
supernova remnant.
question
Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?
answer
Planetary nebula formation is more common.
question
A typical white dwarf is
answer
as massive as the sun but only about as large in size as Earth
question
The maximum mass of a white dwarf is
answer
about 1.4 times the mass of our sun.
question
Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass unit?
answer
The white dwarf will explode completely as a white dwarf supernova.
question
A neutron star is
answer
The remains of a star that died in a massive star supernova (if no black hole was created).
question
Which of the following is NOT a general characteristic of the four Jovian planets in our solar system?
answer
They are higher in average density than are the terrestrial planets.
question
Overall, Jupiter's composition is most like that of
answer
The Sun
question
How do typical wind speeds in Jupiter's atmosphere compare to typical wind speeds on Earth?
answer
They are much faster than hurricane winds on earth.
question
What is the Great Red Spot?
answer
a long-lived, high-pressure storm on Jupiter.
question
Which statement about Io is true?
answer
It is the most volcanically active body in our solar system.
question
Which moon has a thick atmosphere made mostly of nitrogen?
answer
Titan
question
Which moon is considered likely to have a deep, subsurface ocean of liquid water?
answer
Europa
question
Suppose you could float in space just a few meters above Saturn's rings. What would you see as you looked down on the rings?
answer
Countless icy particles, ranging in size from dust grains to large boulders.
question
Which of the following statements best describes the size of the largest asteroid, Ceres?
answer
It is a little less than half the diameter of our moon.
question
If we could put all the asteroids together, their total mass would be
answer
much less than the mass of any terrestrial planet
question
Why didn't a planet form where the asteroid belt is now located?
answer
Gravitational tugs from Jupiter prevented material from collecting together to form a planet.
question
When you see the bright flash of a meteor, what are you actually seeing?
answer
The glow from a pea-size particle and the surrounding air as the particle burns up in our atmosphere.
question
Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different?
answer
It would have only one tail instead of two.
question
When we see a meteor shower, it means that
answer
earth is crossing the orbit of a comet
question
What is Pluto's moon Charon thought to have in common with our own moon?
answer
It probably formed as a result of a giant impact.
question
According to modern science, approximately how old is the sun?
answer
4 1/2 billion years
question
The sun will exhaust its nuclear fuel in about
answer
5 billion years
question
Which of the following correctly describes how the process of gravitational contraction can make a star hot?
answer
When a star contracts in size, gravitational potential energy is converted to thermal energy.
question
What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?
answer
Gravitational foce and outward pressure.
question
The source of energy that keeps the Sun shining today is
answer
Nuclear fusion
question
When we say that the sun is a ball of plasma, we mean that
answer
The sun consists of gas in which many or most of the atoms are ionized (missing electrons).
question
What is the Sun made of (by mass)?
answer
70% hydrogen, 28% helium, 2% other elements.
question
The sun's average surface (photosphere) temperature is about
answer
5,800 K
question
The total amount of power (in watts, for example) that a star radiates into space is called its
answer
Luminosity
question
According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?
answer
Its apparent brightness will DECREASE by a factor of 9.
question
If Star A is closer to us than Star B, then Star A's PARALLAX angle is
answer
larger than that of Star B
question
From hottest to coolest, the order of the spectral types of stars is
answer
OBAFGKM
question
Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?
answer
The star is a member of a binary star system.
question
The axes on a Hertzsprung-Russell (H-R) diagram represent
answer
luminosity and surface temperature
question
How is the lifetime of a star related to its mass?
answer
More massive stars live much shorter lives than less massive stars.
question
All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?
answer
its mass and its stage of life.
question
Star A is identical to Star B, excepts that Star A is twice as far from us as Star B. Therefore:
answer
Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.
question
A star with a parallax angle of 1/20 arc second is
answer
20 parsecs away
question
Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude?
answer
Rigel has a higher surface temperature than Sirius.
question
To calculate the masses of stars in a binary system, we must measure their
answer
orbital period and average orbital distance.
question
You observe a star and you want to plot it on an H-R diagram. You will need to know all of the following, except the star's
answer
Mass.
question
The total amount of power (in watts, for example) that a star radiates into space is its
answer
luminosity.
question
Ten parsecs is about
answer
32.6 light years
question
Our sun is a star of spectral type
answer
G
question
How is the lifetime of a star related to its mass?
answer
More massive stars live much shorter lives than less massive stars.
question
What is the common trait of all main sequence stars?
answer
They generate energy through hydrogen fusion in their core.
question
Our sun is considered to be a
answer
low-mass star
question
Where would a brown dwarf be located on an H-R diagram?
answer
Below and to the right of the lowest part of the main sequence.
question
How does the interstellar medium affect our view of most of the galaxy?
answer
It prevents us from seeing most of the galactic disk with visible and ultraviolet light.
question
How does the diameter of the disk of the Milky Way Galaxy compare to its thickness?
answer
The diameter is about 100 times as great as the thickness.
question
What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy?
answer
The galaxy's bulge
question
The sun's location in the Milky Way Galaxy is
answer
In the galactic disk, roughly halfway between the center and the outer edge of the disk.
question
What do we mean by the interstellar medium?
answer
the gas and dust that lies in between the stars in the Milky Way.
question
How do disk stars orbit the center of the galaxy?
answer
They all orbit in roughly the same plane and in the same direction.
question
How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path?
answer
by applying Newton's version of Kepler's third law to the orbits of the Sun or other nearby stars around the center of the galaxy.
question
What do we mean by the star-gas-star cycle?
answer
It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.
question
The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with
answer
radio telescopes observing at a wavelength of 21 centimeters.
question
Most stars in the Milky Way's halo are
answer
very old.
question
What do halo stars do differently from disk stars?
answer
They orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.
question
Where does most star formation occur in the Milky Way Galaxy?
answer
In the spiral arms.
question
Based on observations, which of the following statements about stars in the Milky Way is generally true?
answer
The older the star, the lower its abundance of heavy elements.
question
How would you expect a star that formed recently in the disk of the galaxy to differ from one that formed early in the history of the disk?
answer
It should have a higher fraction of elements heavier than hydrogen and helium.
question
The most common form of gas in the disk of the Milky Way Galaxy is
answer
atomic hydrogen gas.
question
Over time, the star-gas-star cycle leads the gas in the Milky Way to
answer
have a greater abundance of heavy elements.
question
If you could watch a time-lapse movie of the interstellar medium over hundreds of millions of years, what would you see?
answer
Gas that is often moving at high speed, particularly after one or more supernovae, and constantly changing form between molecular clouds, atomic hydrogen, and hot, ionized bubbles and super bubbles.
question
Why do we believe that most of the Milky Way is in the form of dark matter?
answer
The orbital speeds of stars far from the galactic center are surprisingly high.
question
Spiral arms appear bright because
answer
they contain more hot young stars than other parts of the disk.
question
What is the best evidence for an extremely massive black hole in the center of the Milky Way?
answer
The orbits of stars in the center of the galaxy indicate that the presence of 3 to 4 million solar mass object in a region no larger than our solar system.
question
The reason that small planets tend to lose interior heat faster than larger planets is essential the same reason that
answer
a large baked potato takes longer to cool than a small baked potato.
question
What would happen to Jupiter if we could somehow double its mass?
answer
Its density would increase but its diameter would barely change.
question
What do asteroids and comets have in common?
answer
Most are unchanged since their formation in the solar nebula
question
An icy leftover planetesimal orbiting the sun is
answer
a comet.
question
Why do asteroids and comets differ in composition?
answer
Asteroids formed inside the frost line, while comets formed outside.
question
Which of the following best describes why the sun emits most of its energy in the form of visible light?
answer
Like all objects, the sun emits thermal radiation with a spectrum that depends on its temperature, and the sun's surface temperature is just right for emitting mostly visible light.
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The source of energy that keeps the sun shining today is
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nuclear fusion.
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What is a protostar?
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A star that is still in the process of forming.
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What kind of gas cloud is most likely to give birth to stars?
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A cold, dense gas cloud.
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Pulsars are thought to be
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rapidly rotating neutron stars.
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Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?
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Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.
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Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on) in a high mass star is NOT true?
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Each successive stage creates an element with a higher atomic number and atomic mass number.
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Which event marks the beginning of a supernova?
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The sudden collapse of an iron into a compact ball of neutrons.
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Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?
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We can learn the distance to the galaxy.
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In 1924, Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way, thus putting to rest the idea that it might have been a cloud within our own galaxy. How was he able to prove this?
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He observed individual Cepheid variable stars in Andromeda and applied the period-luminosity relation.
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Why are white dwarf supernovae more useful than massive star supernovae for measuring cosmic distances?
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White dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak luminosities.
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What does cosmological redshift do to light?
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Stretches its wavelength
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A quasar's spectrum is hugely redshifted. What do most astronomers think this large redshift tells us about the quasar?
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The distance to the quasar.
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Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?
answer
Active galactic nuclei tend to become less active as they age.
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Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
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The X-ray source is no more than a few light-days in diameter.
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Why do we call dark matter "dark"?
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It emits no radiation that we have been able to detect.
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Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did NOT contain dark matter. How would their rotation curves be different?
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The orbital speeds would fall off sharply with increasing distance from the galactic center.
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The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they tell us anything about where the dark matter is located within the galaxy?
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Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center.
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Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster?
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The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass.
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Is space expanding within clusters of galaxies?
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NO, because their gravity is strong enough to hold them together even while the universe as a whole expands.
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Which of the following statements about large-scale structure is probably NOT true?
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Clusters and superclusters appear to be randomly scattered about the universe, like dots sprinkled randomly on a wall.
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Based on current evidence, how does the actual average density of matter in the universe compare to the critical density?
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The actual density, even with dark matter included, is less than about a third of the critical density.
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Which of the following statements best describes the current state of understanding regarding the apparent acceleration of the expansion of the universe?
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We have moderately strong evidence that the acceleration is real, but essentially no idea what is causing it.
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Which of the following best summarizes what we mean by dark energy?
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It is a name given to whatever is causing the expansion of the universe to accelerate with time.
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The text states that luminous matter in the Milky Way seems to be much like the tip of an ice berg. This refers to the idea that...
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dark matter represents much more mass and extends much farther from the galactic center than the visible stars of the Milky Way.
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When we say that a cluster of galaxies is acting as a gravitational lens, what do we mean?
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It bends or distorts the light coming from galaxies located behind it.
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What do we mean when we say that particles such as neutrinos or WIMPS are weakly interacting?
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They respond to the weak force but not to the electromagnetic force, which means they cannot emit light.
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The critical density of the universe is the
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Average density the universe would need for gravity to someday halt the current expansion if dark energy did not exist.
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What is the primary form of evidence that has led astronomers to conclude that the expansion of the universe is accelerating?
answer
Observations of WHITE DWARF SUPERNOVAE.
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How do we determine the conditions that existed in the very early universe?
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We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.
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What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?
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The basic chemical composition of the universe had been determined.
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Which of the following is NOT an observed characteristic of the cosmic microwave background?
answer
It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.
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In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why?
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Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.
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Based on the results from the WMAP satellite, the overall composition of the universe is...
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4% ordinary (baryonic matter, 23% nonbaryonic dark matter, 73% dark energy.
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Which of the following best describes the predominant scientific view of the origin of life on Earth?
answer
We may never know precisely how life arose, but current evidence suggests that life probably can arise naturally under the conditions that prevailed on the early earth.
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When we analyze whether a world is a possible home to life, they key thing we look for is
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The past or present existence of liquid water.
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In general, how does the size and location of a star's habitable zone depend on the star's mass?
answer
The smaller (less massive) the star, the smaller and the closer-in the habitable zone.
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We are not yet capable of detecting life on planets around other stars. But as our technology develops, our first real chance of detecting such life will probably come from
answer
examining spectral lines from the atmosphere of distant planets.
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