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90 Cards in this Set

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  • Back
The visible "surface" of the Sun is called the
Photosphere
The highest temperature in the solar atmosphere is found in
The corona
What is the visible evidence of overturning gases (convection) in the upper layer of the Sun's interior?
The granular appearance (granules)
Sunspots are cooler than the surrounding photosphere because
The strong magnetic field inhibits the currents of hot gas rising from below.
It appears that the differential rotation of the Sun winds up the magnetic fields. This is useful in explaining
The sunspot cycle
When sunspots increase in number, solar activity, such as the number of solar flares
Increases
The Sun is supported against the crushing force of its own gravity by
Gas pressure
The Sun produces its energy from
Fusion of hydrogen into helium
The apparent shift in the position of an object, such as a star, can be used to measure distance is
Parallax
The H-R diagram compares the intrinsic brightness of a star to its
Temperature or color
In the H-R diagram, 90% of all stars fall
On the main sequence
Where on the H-R diagram are the extremely bright, hot, and massive stars found?
The upper left corner of the main sequence
Where on the H-R diagram are the extremely bright, but cool stars?
The red giant branch
Where on the H-R diagram are the very small, but very hot stars?
The white dwarf branch
Which of the following star magnitudes is the brightest?
0
A star that is cool and very luminous must have
A very large radius
By observing the orbital periods of binary stars, astronomers can determine what property of stars?
Mass
Spectral class is which kind of sequence?
Temperature
Composition of a star can be measured from
Its pattern of spectral lines
Motion of a star away from or toward Earth can be measured by
The shift in its spectral lines
The element that makes up most of the mass of interstellar medium is
Hydrogen
To collapse into stars, an interstellar cloud must be
Cold and dense
The time a protostar takes to contract from a cool interstellar gas cloud to a main sequence star depends on its
Mass
Which of the following causes protostars to heat?
Increased pressure from the weight of the collapse
Nuclear fusion of hydrogen into helium occurs in the cores of
Main sequence stars
The mass-luminosity relation exists because
Stars support their weight by making energy.
When the core of a star is depleted of hydrogen causing the core to shrink and become hotter, the star itself becomes
Larger and cooler
The next stage in the evolution of the Sun is
A red giant
Main sequence stars of which classification spend the most time on the Hertzsprung-Russell diagram?
M
A turn-off point on the H-R diagram of a star cluster is used to determine the
The age of the cluster
What kinds of objects lie in the disk of the Milky Way galaxy?
All of the above
How does the interstellar medium obscure your view of most of the galaxy?
It absorbs visible, ultraviolet, and some infrared light.
All the iron on Earth originated from
Nuclear fusion within the cores of high-mass stars
What is the most common form of gas in the interstellar medium?
Atomic hydrogen
Where do most dust grains form?
In the winds of red giant stars
Suppose you read somewhere that 10% of the matter in the Milky Way is in the form of dust grains. Should you be surprised? If so, why?
The 10% figure cannot be correct, because dust grains are solid but only about 2% of the matter in the galaxy is made of anything besides hydrogen and helium.
How do you learn about what is going on in the center of the Milky Way galaxy?
You cannot see the galactic center with visible or ultraviolet light, but radio and X-rays from the center can be detected.
How do you know that there is much more mass in the halo of the galaxy than in the disk?
Stars in the outskirts of the Milky Way orbit the galaxy at much higher speeds than you would expect if all the mass were concentrated in the disk.
Why do astronomers believe that 90% of the mass of the Milky Way is in the form of dark matter?
The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.
Compared with stars in the disk, the orbits of stars in the halo
Are elliptical, with random orientation
Compared with the Sun, most stars in the halo are
Old, red, dim, and have fewer heavy elements
How does the interstellar medium affect your view of most of the galaxy?
It prevents you from seeing most of the galactic disk with visible, ultraviolet, and some infrared light.
The image of the galaxy in radio emission from CO, mapping the distribution of molecular clouds, is closest to the image of the galaxy in
Infrared emission from interstellar dust grains
Suppose a scientist holds a press conference, at which he claims that 10% of the matter in the Milky Way is in the form of dust grains. In light of what you think you now know, does his claim seem reasonable? Why or why not?
The 10% figure seems far too high because there are not enough of the kinds of elements that can take solid form in the galaxy.
Which of the following does not accurately describe what is observed toward the Galactic center?
At optical wavelengths, you see a cluster of old, red stars.
What evidence supports the theory that there is a black hole at the center of this galaxy?
The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about one parsec across.
What is Sgr A*?
A source of bright radio emission in the center of the galaxy
Suppose you want to observe and study the radiation from gas inside an interstellar bubble. Which of the following observatories will be most useful?
The Chandra X-ray Observatory
How should you expect that the interstellar medium of the Milky Way to be different in 50 billion years?
The total amount of gas will be much less than it is today.
The most common form of gas in the disk of the Milky Way galaxy is
Atomic hydrogen gas
All the following types of objects are found almost exclusively in the disk, rather than halo of the Milky Way except:
Globular clusters
Red and orange stars are found evenly spread throughout the galactic disk, but blue stars are typically found
Only near star-forming regions
Most nearby stars move relative to the Sun at speeds below about 30 km/s. Suppose you observe a Suppose you discover a nearby star that is moving much faster than this (say, 300 km/s). Which of the following is a likely explanation for its high speed?
It is probably a halo star, which is currently passing through the disk.
Why do scientists believe that most of the mass of the Milky Way is in the form of dark matter?
The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.
If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in?
Warm, rarefied clouds of atomic hydrogen
What do astronomers consider heavy elements?
All elements besides hydrogen and helium
Which of the following statements is not true of the object known as Sgr A* in the center of this Galaxy?
Its accretion disk is so large that it shines brightly in visible light.
Why are spiral arms bright?
Because they contain more hot young stars than other parts of the disk
Approximately how long does it take the Sun to orbit the Milky Way Galaxy?
230 million years
What produces the 21-cm line that is used to map out the Milky Way Galaxy?
Atomic hydrogen
Suppose that you look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?
The one that is farthest away
Which of the following types of galaxies are most spherical in shape?
Ellipticals
Which of the following types of galaxies are reddest in color?
Ellipticals
Compared to spiral galaxies, elliptical galaxies are
Redder and rounder
The disk component of a spiral galaxy includes which of the following parts?
Spiral arms
Which of the following is true about irregular galaxies?
They were more common when the universe was younger.
What two quantities did Edwin Hubble compare to discover the expansion of the universe?
Velocity and distance
What is the most accurate way to determine the distance to a nearby star?
Stellar parallax
Which of the following gives the two main assumptions of theoretical models of galaxy evolution?
Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
All of the above
What evidence suggests that the Milky Way contains dark matter?
You observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that you can see.
If there is no dark matter in the Milky Way Galaxy, what is the best alternative explanation for the observations?
The current understanding of gravity is not correct for galaxy-size scales.
How do you determine the amount of dark matter in elliptical galaxies?
You measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit.
Which of the following is not evidence for dark matter?
The expansion of the universe
Why isn't space expanding within systems such as this solar system or the Milky Way?
Their gravity is strong enough to hold them together against the expansion of the universe.
If all the "dark matter" in the universe were to be instantaneously removed, which of the following would not happen?
The solar system would fly apart.
Which model of the universe gives the youngest age for its present size?
A recollapsing universe
What does the universe look like on very large scales?
Galaxies appear to be distributed in chains and sheets that surround great voids
Which of the following is not one of the three main strategies used to measure the masses of galaxy clusters?
Measuring the temperatures of stars in the halos of the galaxies
Which of the following statements best summarizes what studies of the masses of individual galaxies and of clusters of galaxies say about dark matter?
Dark matter is the dominant form of mass in both clusters and individual galaxies.
The Planck era refers to the time
Before the Planck time
Why can't current theories describe what happened during the Planck era?
Scientists do not yet have a theory that links quantum mechanics and general relativity.
What is meant by inflation?
A sudden expansion of the universe after the strong force froze out from the GUT force
What direct evidence exists that the weak and electromagnetic forces were once unified as a single electroweak force?
Particle accelerators on Earth can reach energies equivalent to the high temperatures of this era and have produced particles predicted by the electroweak theory.
What is postulated to have caused a sudden inflation of the early universe?
The "freezing out" of the strong force from the GUT force
Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question?
Why is the sky dark at night?
The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?
The first theory predicts the existence of and the specific characteristics of the observed cosmic microwave background while the second theory correctly predicts the observed overall chemical composition of the universe.
Which statement about the cosmic microwave background is not true?
It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
Based on the Big Bang theory, what do observations of the cosmic microwave background and of chemical abundances in the universe suggest about dark matter?
Much of the dark matter must be made of non-ordinary (nonbaryonic) matter, such as WIMPs.
Which of the following observations cannot be explained by the Big Bang theory unless you assume that an episode of inflation occurred?
The fact that the temperature of the cosmic microwave background is almost the same everywhere