Astronomy 18, Interstellar Medium
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Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear
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redder
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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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In which wavelengths have the births of new stars been best mapped recently?
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infrared
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Molecular clouds are much warmer than typical interstellar gas clouds.
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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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Hydrogen is the major gas in the interstellar medium.
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true
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Which of these is not a consequence of dust in the interstellar medium?
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red light from the emission nebulae
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Interstellar matter is distributed very evenly through the galaxy.
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false
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What two things are needed to create an emission nebulae?
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hot stars and interstellar gas, particularly hydrogen
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Neutral hydrogen is most obvious in the electromagnetic spectrum at:
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21 cm in the radio region
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The Local Bubble was probably created by
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a nearby supernova perhaps 300,000 years ago, brighter than the Full Moon
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A reflection nebula is caused by
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starlight scattered by dust particles
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What effect does 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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Which statement about the dark nebulae is true?
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They can be penetrated only with longer wavelengths such as radio and infrared
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The polarization of light passing through the dust grains shows that
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Both A and B are correct
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The overall dimming of starlight by interstellar matter is called
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extinction
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The most common molecule in a molecular cloud is:
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molecular hydrogen, H2
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Why is 21-cm radiation so important to the study of interstellar matter and the Galaxy?
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Emitted by hydrogen, it passes thru interstellar dust and lets us to map the entire Galaxy.
