Exam 3 Preparation- AST (module 12 quiz) – Flashcards
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What kinds of objects lie in the disk of our galaxy?
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all of the above
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Where does most star formation occur in the Milky Way today?
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in the spiral arms
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How does the interstellar medium obscure our view of most of the galaxy?
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The small mixture of dust grains in the interstellar medium absorbs visible light
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What kinds of objects lie in the halo of our galaxy?
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globular clusters
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What evidence supports the existence of a black hole in the center of our galaxy?
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The motions of the gas and stars at the center indicate that it contains 4 million solar masses within a region only 3 light-years across
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Compared with stars in the disk, orbits of stars in the halo
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are elliptical, with random orientations
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Harlow Shapely concluded that the sun was not located in the center of the Milky Way galaxy by
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mapping the distribution of globular clusters in the galaxy
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Where do most dust grains form?
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in the winds of red giant stars
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How do we learn about the conditions at the center of our own galaxy, the Milky Way?
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While we cannot see the galactic center with the visible or ultra violet light, radio and x-rays from the center can be detected and used to determine the conditions there
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The image of our galaxy in radio emission from carbon monoxide maps the distribution of molecular clouds. Which of the following would give a similar picture of our galaxy?
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Infrared emission from interstellar dust grains
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What is Sgr Aa*-?
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A source of bright radio emission in the center of our galaxy
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Approximately how far is the sun from the center of the galaxy?
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28,000 light-years
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What is a shock wave?
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A pressure wave that moves faster than the speed of sound
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How are interstellar bubbles made?
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By the winds of massive stars and supernovae explosions
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If you were to take a voyage through the entire disk of the Milky Way, what kind of material would you spend most of your time in?
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Rarefied clouds of atomic hydrogen
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What is the most common form of gas in the interstellar medium?
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atomic hydrogen
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Over time, what is the net effect of the star-gas-star cycle in the Milky Way?
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The total mass in the galaxy's interstellar medium is gradually reduced, and the remaining gas is continually enriched in heavy elements
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How can we see through the interstellar medium?
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By observing at wavelengths (high-energy X-rays and long wavelength radio waves) that are not absorbed by interstellar dust
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Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
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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
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Where are most heavy elements made?
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In stars and supernovae
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Sound waves in the interstellar medium
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Can travel through the gas, but the very low density of the interstellar medium makes them inaudible
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What produces the 21 cm radio line that we can be used to map the Milky Way Galaxy
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Atomic Hydrogen
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The galactic center lies in the direction of which constellation
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Orion
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What is the most abundant molecule in interstellar clouds besides molecular hydrogen?
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Carbon Monoxide
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Suppose you read somewhere that 10 percent of the matter in the Milky Way is the form of dust grains. Should you be surprised? If so, why?
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The fraction of 10 percent cannot be correct. Dust grains are solid and only 2 percent of the matter in the galaxy is made of anything besides hydrogen and helium
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What is the thickness of the disk of the Milky Way?
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1,000 light years
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What makes up the interstellar medium?
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Gas and dust
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What elements do astronomers consider heavy elements?
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All elements besides hydrogen and helium
