A) only hydrogen.
B) 90% hydrogen, 9% helium by weight.
C) 10% hydrogen, 90% helium by numbers of atoms.
D) some hydrogen, but mainly carbon dioxide.
E) ammonia, methane, and water vapor.
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B
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A) there are no stars in these areas.
B) stars in that region are hidden by interstellar gas.
C) stars in that region are hidden by dark dust particles.
D) many brown dwarfs in those areas absorb light which they turn into heat.
E) many black holes absorb all light from those directions.
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A) Hydrogen and helium are the chief absorbing and scattering agents.
B) They block the vast majority of radio waves from our Galaxy.
C) They can be penetrated only with longer wavelengths such as radio and infrared.
D) They comprise the majority of the mass of the Galaxy.
E) They can be penetrated only with shorter waves, such as UV and X-ray.
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A) there is very little interstellar matter.
B) molecules always produce narrow absorption lines.
C) most of the matter is ionized, and atoms moving fast produce sharp lines.
D) the matter is at a low temperature, and atoms are almost still.
E) All of the above are correct.
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D
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A) diamonds
B) cubes
C) spheres
D) disks
E) rodlike
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The predominant bright red is the emissi...View Answer
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A) It helps locate the galactic core in Sagittarius.
B) Emitted by hydrogen, it passes through interstellar dust and lets us map the entire Galaxy.
C) Emitted by carbon monoxide, it passes through interstellar gas and lets us see places rich inorganic molecules around the Galaxy.
D) It is emitted by most stars, enabling astronomers to map the entire Galaxy.
E) It is emitted only in hot regions of star formation, so the pattern of the spiral arms of theGalaxy can be mapped.
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A) The cloud is an illusion, for the dust is evenly distributed around the Galaxy.
B) Dust clouds do radiate energy, but not as much light as the stars do.
C) It is ice, not dust, which make them look dark.
D) They contain much more gas than dust.
E) All of the above are correct.
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In some cases, they are not thick enough...View Answer
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Neutral hydrogen dominates the compositi...View Answer
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A) black, because of dust
B) blue from the scattering of light off the tiny molecules
C) blue due to ionized helium atoms
D) red due to ionized hydrogen atoms
E) red because of reddening by dust
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A) extinction.
B) reddening.
C) absorption.
D) emission.
E) scattering.
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A
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A) visible light.
B) microwaves.
C) ultraviolet radiation.
D) infrared heat.
E) X-rays and gamma rays.
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A) The density or pressure of this gas is much lower than can be produced in a laboratory.
B) The laws of physics are not the same in space as they are on Earth.
C) There are unknown elements in space that do not correspond to elements found on Earth.
D) There are molecules found in meteorites and interstellar dust that are not found on Earth.
E) All of the above are true.
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The Galaxy's magnetic field al...View Answer
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A) 0 K.
B) 2.73 K.
C) 100 K.
D) 3,000 K.
E) 6,000 K.
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The grain size of the dust is ...View Answer
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