If all the stars on the main sequence of a star cluster are typically only one-hundredth as bright as their main-sequence counterparts in the Hyades Cluster, then that cluster's distance is
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10 times as far as the Hyades's distance.
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Why do virtually all the galaxies in the universe appear to be moving away from our own?
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Because expansion causes all galaxies to move away from nearly all others.
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Which of these galaxies is most likely to be oldest?
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a galaxy in the local group
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When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was
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4 billion years old
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Which of these items is a key assumption in our most successful models for galaxy formation?
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Some regions of the universe were slightly denser than others.
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The primary source of a quasar's energy is
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gravitational potential energy.
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In a photo like the Hubble Deep Field (the figure in your textbook), we see galaxies in many different stages of their lives. In general, which galaxies are seen in the earliest (youngest) stages of their lives?
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The galaxies that are farthest away
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The most basic difference between elliptical galaxies and spiral galaxies is that ________.
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elliptical galaxies lack anything resembling the disk of a spiral galaxy
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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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Suppose that Hubble's constant were 20 kilometers per second per million light-years. How fast would we expect a galaxy 100 million light-years away to be moving? (Assume the motion is due only to Hubble's law.)
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away from us at 2,000 km/s
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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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Which statement below correctly describes the relationship between expansion rate and age for the universe?
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The faster the rate of expansion, the younger the age of the universe.
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Why can't we see past the cosmological horizon?
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Beyond the cosmological horizon, we would be looking back to a time before the universe was born.
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We can study how galaxies evolve because ________.
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the farther away we look, the further back in time we se
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Interactions among galaxies also are thought to influence a galaxy's type in at least some cases. Which of the following does not support the idea that interactions can shape galaxies?
answer
The fact that more distant galaxies have larger redshifts
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A standard candle is ________.
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a light source of known luminosity
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What two observable properties of a Cepheid variable are directly related to one another?
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The period between its peaks of brightness and its luminosity
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What does Hubble's law tell us?
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The more distant a galaxy, the faster it is moving away from us.
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Given that white dwarf supernovae are such good standard candles, why don't we use them to measure the distance to all galaxies?
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They are rare events, so we have observed them in only a tiny fraction of all galaxies.
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Although the entire universe may be much larger than our observable universe, we can see only within our observable universe. The "boundary" of our observable universe is called ________.
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the cosmological horizon
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Cosmological redshift is the result of ________.
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the expansion of the universe
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Current estimates place the age of the universe at about ________.
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14 billion years
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Why are collisions between galaxies more likely than collisions between stars within a galaxy?
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Relative to their sizes, galaxies are closer together than stars.
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Why should galaxy collisions have been more common in the past than they are today?
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Galaxies were closer together in the past because the universe was smaller.
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Which of the following types of galaxies appear reddest in color?
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ellipticals
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Compared to spiral galaxies, elliptical galaxies are
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redder and rounder
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What is the major difference between an elliptical galaxy and a spiral galaxy?
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An elliptical galaxy lacks a disk component.
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Which of the following is a consequence of Hubble's Law?
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the more distant a galaxy is from us, the faster it moves away from us
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What makes white-dwarf supernovae very good standard candles for distance measurements?
answer
They are very bright, so they can be used to determine the distances to galaxies billions of light-years away. And they should all have approximately the same luminosity.
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Dr. Smith believes that the Hubble constant is H0 = 25 km/s/Mly while Dr. Jones believes it is H0 = 19 km/s/Mly. Which statement below automatically follows?
answer
Dr. Smith believes that the universe is younger than Dr. Jones believes.
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Dr. X believes that the Hubble constant is H0 = 20 km/s/Mly while Dr. Y believes it is H0 = 24 km/s/Mly. Which statement below automatically follows?
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Dr. X believes that the Hubble constant is H0 = 20 km/s/Mly while Dr. Y believes it is H0 = 24 km/s/Mly. Which statement below automatically follows?
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Which of the following gives the two main assumptions of theoretical models of galaxy evolution?
answer
Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
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What evidence supports the idea that a collision between two spiral galaxies might lead to the formation of a single elliptical galaxy?
answer
observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies
observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy
observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies
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Which of the following cannot be true of the very first stars formed in the Universe?
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Some may have had rocky planets around them.
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In a uniformly expanding universe, which statement best describes the situation as viewed from an observer in Galaxy C (not the Milky Way Galaxy)?
answer
Galaxy C observer sees all other galaxies moving away from itself.
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Ming measures a recession velocity of 2000 km/sec for a galaxy. About how far away is that galaxy if the Hubble constant is 20 (km/sec)/million light years? (Hint: be sure to check the units in your calculation.)
answer
100 million light years
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