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Rio Salado AST101
AST101 flashcards
90
Astronomy
Undergraduate 1
11/24/2015

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