Astronomy Chapters 18 & 19 – Flashcards
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Interstellar gas is composed of:
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90% hydrogen, 9% helium by weight.
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What effect do even thin clouds of dust have on light passing through them?
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It dims and reddens the light of all more distant stars.
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Some regions along the plane of the Milky Way appear dark because:
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stars in that region are hidden by dark dust particles.
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The spectra of interstellar gas clouds show that they have the same basic composition as:
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stars.
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Hydrogen is the major gas in the interstellar medium.
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True.
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There is as much mass in the voids between the stars as in the stars themselves.
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True.
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The "Local Bubble" was probably created by a nearby supernova in the distant past.
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False.
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Emission nebulae like M42 occur only near stars that emit large amounts of:
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ultraviolet radiation.
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What is the primary visible color of an emission nebula?
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Red, due to ionized hydrogen atoms.
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Emission nebula appear red because they are associated with cool red giant stars.
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False.
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The compositions of dark clouds can be determined through absorption spectra.
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True.
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A dark cloud can be detected if it happens to block the light emitted by more distant stars.
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True.
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The most common molecule in a molecular cloud is:
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molecule hydrogen, H2.
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Complex molecules in space are found:
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in dense dust clouds.
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Which of the following has NOT yet been observed in space?
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DNA.
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Our Sun, along with most of the stars in our neighborhood, probably formed:
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billions of years ago.
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What is the force that keeps a main sequence star from blowing apart?
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gravitation.
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The birth of stars is a battle between gravity and radiation pressure.
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True.
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The fundamental difference between a protostar and a star is that the latter has nuclear fusion as its energy source and the former does not.
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True.
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Which event marks the birth of a star?
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Fusion of hydrogen atoms into helium atoms.
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A newly formed protostar will radiate primarily at which wavelength?
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infrared.
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What is the force that keeps a main sequence star from collapsing on itself?
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Radiation pressure.
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At the end of the Kelvin-Helmholtz contraction a star is hundreds of times brighter than it will be as a main sequence star.
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True.
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A cloud fragment too small to collapse into a main sequence star becomes a:
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brown dwarf.
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The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its:
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mass.
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Besides mass the other factor that influences where a star appears on the main sequence is:
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chemical composition of the cloud.
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Atomic bomb tests demonstrated which aspect of star formation?
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A shock wave surrounding and compressing a molecular cloud.
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Why are star clusters almost ideal "laboratories" for stellar studies?
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Stars in clusters have the same age, similar composition, and are at the same distance away.
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Star clusters have been observed within dark nebulae with:
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infrared observations.
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What are the characteristics of globular cluster stars?
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Old age and hundreds of thousands to millions of member stars.
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All globular clusters in our Milky Way are about how old?
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Around ten billion years old.
