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Question 1 Some regions of the Milky Way’s disk appear dark because there are no stars there. stars in that direction are obscured by interstellar gas. stars in that direction are obscured by interstellar dust. numerous black holes capture all the starlight behind them. Answer: c © 2017 Pearson Education, Inc.

Question 1 Some regions of the Milky Way’s disk appear dark because there are no stars there. stars in that direction are obscured by interstellar gas. stars in that direction are obscured by interstellar dust. numerous black holes capture all the starlight behind them. Explanation: Dust grains are about the same size as visible light, and they can scatter or block the shorter wavelengths. © 2017 Pearson Education, Inc.

Question 2 When a star’s visible light passes through interstellar dust, the light we see is dimmed and reddened. appears to twinkle. is Doppler shifted. turns bluish in color. ionizes the dust and creates emission lines. Answer: a © 2017 Pearson Education, Inc.

Question 2 When a star’s visible light passes through interstellar dust, the light we see is dimmed and reddened. appears to twinkle. is Doppler shifted. turns bluish in color. ionizes the dust and creates emission lines. Explanation: The same process results in wonderful sunsets, as dust in the air scatters the Sun’s blue light, leaving dimmer, redder light. © 2017 Pearson Education, Inc.

Question 3 Astronomers use the term nebula to refer to outer envelopes of dying stars that drift gently into space. remnants of stars that die by supernova. clouds of gas and dust in interstellar space. distant galaxies seen beyond our Milky Way. All of the above are correct. Answer: e © 2017 Pearson Education, Inc.

Question 3 Astronomers use the term nebula to refer to outer envelopes of dying stars that drift gently into space. remnants of stars that die by supernova. clouds of gas and dust in interstellar space. distant galaxies seen beyond our Milky Way. All of the above are correct. Explanation: Nebula refers to any fuzzy patch—bright or dark—in the sky. © 2017 Pearson Education, Inc.

Question 4 Interstellar gas is composed primarily of 90% hydrogen, 9% helium, and 1% heavier elements. molecules including water and CO2. 50% hydrogen and 50% helium. hydrogen, oxygen, and nitrogen. 99% hydrogen and 1% heavier elements. Answer: a © 2017 Pearson Education, Inc.

Question 4 Interstellar gas is composed primarily of 90% hydrogen, 9% helium, and 1% heavier elements. molecules including water and CO2. 50% hydrogen and 50% helium. hydrogen, oxygen, and nitrogen. 99% hydrogen and 1% heavier elements. Explanation: The composition of interstellar gas mirrors that of the Sun, stars, and the jovian planets. © 2017 Pearson Education, Inc.

Question 5 The reddish color of emission nebulae indicates that gas and dust are moving away from Earth. hydrogen gas is present. dying stars have recently exploded. cool red stars are hidden inside. dust is present. Answer: b © 2017 Pearson Education, Inc.

Question 5 The reddish color of emission nebulae indicates that gas and dust are moving away from Earth. hydrogen gas is present. dying stars have recently exploded. cool red stars are hidden inside. dust is present. Explanation: Glowing hydrogen gas emits red light around the Horsehead Nebula. © 2017 Pearson Education, Inc.

Question 6 Twenty-one-centimeter radiation is important because its radio waves pass unaffected through clouds of interstellar dust. it arises from cool helium gas present throughout space. it can be detected with optical telescopes. it is produced by protostars. it reveals the structure of new stars. Answer: a © 2017 Pearson Education, Inc.

Question 6 Twenty-one-centimeter radiation is important because its radio waves pass unaffected through clouds of interstellar dust. it arises from cool helium gas present throughout space. it can be detected with optical telescopes. it is produced by protostars. it reveals the structure of new stars. Explanation: Cool atomic hydrogen gas produces 21-cm radio radiation as its electron “flips” its direction of spin. © 2017 Pearson Education, Inc.

Question 7 Complex molecules in space are found in the photospheres of red giant stars. primarily inside dense dust clouds. in the coronas of stars like our Sun. scattered evenly throughout interstellar space. surrounding energetic young stars. Answer: b © 2017 Pearson Education, Inc.

Question 7 Complex molecules in space are found in the photospheres of red giant stars. primarily inside dense dust clouds. in the coronas of stars like our Sun. scattered evenly throughout interstellar space. surrounding energetic young stars. Explanation: A radio telescope image of the outer portion of the Milky Way reveals molecular cloud complexes. © 2017 Pearson Education, Inc.

Question 8 Stars are often born within groups known as clans. spiral waves. aggregates. clusters. swarms. Answer: d © 2017 Pearson Education, Inc.

Question 8 Stars are often born within groups known as clans. spiral waves. aggregates. clusters. swarms. Explanation: The Pleiades—a nearby open cluster—is a group of relatively young stars about 400 light-years from the Sun. © 2017 Pearson Education, Inc.

Question 9 Very young stars in small clusters of 10–100 members are known as OB associations. molecular cloud complexes. aggregates. globular clusters. hives. Answer: a © 2017 Pearson Education, Inc.

Question 9 Very young stars in small clusters of 10–100 members are known as OB associations. molecular cloud complexes. aggregates. globular clusters. hives. Explanation: NGC 3603 is a newborn cluster of hot young blue type O and B stars—a perfect OB association. © 2017 Pearson Education, Inc.

Question 10 All stars in a stellar cluster have roughly the same temperature. color. distance. mass. luminosity. Answer: c © 2017 Pearson Education, Inc.

Question 10 All stars in a stellar cluster have roughly the same temperature. color. distance. mass. luminosity. Explanation: Stars in the Pleiades cluster vary in temperature, color, mass, and luminosity, but all lie about 440 light-years away. © 2017 Pearson Education, Inc.

Question 11 Globular clusters are typically observed in the plane of our Galaxy. above or below the plane of our Galaxy. near our Sun. in the hearts of other galaxies. Answer: b © 2017 Pearson Education, Inc.

Question 11 Globular clusters are typically observed in the plane of our Galaxy. above or below the plane of our Galaxy. near our Sun. in the hearts of other galaxies. Explanation: Globular clusters orbit the center of the Milky Way and are usually seen above or below the galactic plane far from our Sun. © 2017 Pearson Education, Inc.

Question 12 Stars in clusters and associations have about the same age. temperature. mass. color. luminosity. Answer: a © 2017 Pearson Education, Inc.

Question 12 Stars in clusters and associations have about the same age. temperature. mass. color. luminosity. Explanation: Most of the stars in a cluster form about the same time. Stars in the Omega Centauri globular cluster are estimated to be about 14 billion years old. © 2017 Pearson Education, Inc.

Question 13 Objects more massive than our Sun form into stars much slower, over billions of years. in about the same time. much faster, over tens of thousands of years. not at all—they are unstable. Answer: c © 2017 Pearson Education, Inc.

Question 13 Objects more massive than our Sun form into stars much slower, over billions of years. in about the same time. much faster, over tens of thousands of years. not at all—they are unstable. Explanation: More mass → faster collapse More mass → faster start of fusion reactions More mass → a hotter, more luminous main-sequence star © 2017 Pearson Education, Inc.

Question 14 How do single stars form within huge clouds of interstellar gas and dust? Clouds fragment into smaller objects, forming many stars at one time. One star forms; other matter goes into planets, moons, asteroids, and comets. Clouds rotate and throw off mass until only enough is left to form one star. Answer: a © 2017 Pearson Education, Inc.

Question 14 How do single stars form within huge clouds of interstellar gas and dust? Clouds fragment into smaller objects, forming many stars at one time. One star forms; other matter goes into planets, moons, asteroids, and comets. Clouds rotate and throw off mass until only enough is left to form one star. Explanation: The theory of star formation predicts stars in a cluster would form about the same time. © 2017 Pearson Education, Inc.

Question 15 What is a T-Tauri star? A collapsing cloud of gas about to become a protostar A dying star A cool main-sequence star A star releasing a planetary nebula A protostar about to become a star Answer: e © 2017 Pearson Education, Inc.

Question 15 What is a T-Tauri star? A collapsing cloud of gas about to become a protostar A dying star A cool main-sequence star A star releasing a planetary nebula A protostar about to become a star Explanation: T-Tauri stars often show jets of gas emitted in two directions— bipolar flow—suggesting they are not yet stable. © 2017 Pearson Education, Inc.

Question 16 A key feature of globular clusters is that they have very few cool stars. the oldest stars in our Galaxy. lots of massive main-sequence stars. stars with very different ages. high concentrations of metals. Answer: b © 2017 Pearson Education, Inc.

Question 16 A key feature of globular clusters is that they have very few cool stars. the oldest stars in our Galaxy. lots of massive main-sequence stars. stars with very different ages. high concentrations of metals. Explanation: The H–R diagram of a globular cluster has a low “turnoff point,” indicating its extreme age. © 2017 Pearson Education, Inc.