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Question 1 The location of the Galactic center was identified early in the 20th century using supernova remnants. white dwarf stars in the spiral arms. red giant variable stars in globular clusters. bright O and B stars in open clusters. X-ray sources. Answer: c © 2017 Pearson Education, Inc.

Question 1 The location of the Galactic center was identified early in the 20th century using supernova remnants. white dwarf stars in the spiral arms. red giant variable stars in globular clusters. bright O and B stars in open clusters. X-ray sources. Explanation: Harlow Shapley used pulsating RR-Lyrae variables as distance indicators to the globular clusters. He then deduced the distance and direction of the Milky Way’s center. © 2017 Pearson Education, Inc.

Question 2 Our Sun is located in the Milky Way Galaxy about 30 Kpc from the center in the halo. 30,000 light-years from the center in a globular cluster. at the outer edge of the Galactic disk, in the plane. about halfway from the center, in the spiral arms. in the bulge, near the Orion arm. Answer: d © 2017 Pearson Education, Inc.

Question 2 Our Sun is located in the Milky Way Galaxy about 30 Kpc from the center in the halo. 30,000 light-years from the center in a globular cluster. at the outer edge of the Galactic disk, in the plane. about halfway from the center, in the spiral arms. in the bulge, near the Orion arm. Explanation: The Sun orbits the center of the Galaxy within the disk, taking about 225 million years to complete one orbit. © 2017 Pearson Education, Inc.

Question 3 The period–luminosity relationship is a crucial component of measuring distances with Cepheid variable stars. identifying the mass of the Galaxy’s central black hole. determining the masses of stars in an eclipsing binary system. using spectroscopic parallax to measure distances to stars. Answer: a © 2017 Pearson Education, Inc.

Question 3 The period–luminosity relationship is a crucial component of measuring distances with Cepheid variable stars. identifying the mass of the Galaxy’s central black hole. determining the masses of stars in an eclipsing binary system. using spectroscopic parallax to measure distances to stars. Explanation: Cepheid variable stars with longer periods have higher actual luminosities; short-period Cepheids are dimmer. © 2017 Pearson Education, Inc.

Question 4 High-speed motion of gas and stars near the Milky Way Galaxy’s center is explained by tidal forces from the Andromeda Galaxy. accretion disks around neutron stars. gamma-ray bursts. gravitation from globular clusters. a supermassive black hole. Answer: e © 2017 Pearson Education, Inc.

Question 4 High-speed motion of gas and stars near the Milky Way Galaxy’s center is explained by tidal forces from the Andromeda Galaxy. accretion disks around neutron stars. gamma-ray bursts. gravitation from globular clusters. a supermassive black hole. Explanation: Recent observations estimate the black hole to be 4 million solar masses. © 2017 Pearson Education, Inc.

Question 5 Detailed measurements of the disk suggest that our Milky Way is a spiral galaxy. a barred spiral galaxy. an elliptical galaxy. a quasar. an irregular galaxy. Answer: b © 2017 Pearson Education, Inc.

Question 5 Detailed measurements of the disk suggest that our Milky Way is a spiral galaxy. a barred spiral galaxy. an elliptical galaxy. a quasar. an irregular galaxy. Explanation: Measurements imply the disk has a diameter about 30 times the disk thickness. Embedded in the disk are spiral arms and a short bar near the center. © 2017 Pearson Education, Inc.

Question 6 What two observations allow us to estimate the Galaxy’s mass? The Sun’s mass and velocity in orbit around the Galactic center The rotation of the bulge and disk components The Sun’s age and age of the globular cluster stars The motion of spiral arms and the mass of the central black hole The orbital period and distance from the Galactic center of objects near the edge of the Galaxy Answer: e © 2017 Pearson Education, Inc.

Question 6 What two observations allow us to estimate the Galaxy’s mass? The Sun’s mass and velocity in orbit around the Galactic center The rotation of the bulge and disk components The Sun’s age and age of the globular cluster stars The motion of spiral arms and the mass of the central black hole The orbital period and distance from the Galactic center of objects near the edge of the Galaxy Explanation: Use the modified form of Kepler’s law to find the mass: total mass = (orbital size)3 / (orbital period)2 © 2017 Pearson Education, Inc.

Question 7 In the formation of our Galaxy, the spiral arms formed first. globular clusters formed first. disk component started out thin and grew. spiral density waves formed first. bar in the bulge formed first. Answer: b © 2017 Pearson Education, Inc.

Question 7 In the formation of our Galaxy, the spiral arms formed first. globular clusters formed first. disk component started out thin and grew. spiral density waves formed first. bar in the bulge formed first. Explanation: Globular clusters contain very old stars, no gas or dust, and orbit around the center randomly. © 2017 Pearson Education, Inc.

Question 8 Twenty-one centimeter radio radiation is useful in studying our Galaxy because the waves penetrate dusty cocoons to reveal star formation. it reflects from the Galaxy’s core. the waves are not absorbed by Galactic black holes. it can be used to map out the cool hydrogen in spiral arms. radio waves provide a distance measurement like parallax. Answer: d © 2017 Pearson Education, Inc.

Question 8 Twenty-one centimeter radio radiation is useful in studying our Galaxy because the waves penetrate dusty cocoons to reveal star formation. it reflects from the Galaxy’s core. the waves are not absorbed by Galactic black holes. it can be used to map out the cool hydrogen in spiral arms. radio waves provide a distance measurement like parallax. Explanation: The Doppler shifts of 21-cm radiation from hydrogen in the spiral arms provides astronomers with a tool to map out the Galaxy’s structure. © 2017 Pearson Education, Inc.

Question 9 Which of these is NOT a typical part of our Galaxy’s spiral arms? OB associations Open clusters Giant molecular clouds Emission nebulae Globular clusters Answer: e © 2017 Pearson Education, Inc.

Question 9 Which of these is NOT a typical part of our Galaxy’s spiral arms? OB associations Open clusters Giant molecular clouds Emission nebulae Globular clusters Explanation: The spiral arms contain gas, dust, molecular clouds, new clusters, and Population I stars. © 2017 Pearson Education, Inc.

Question 10 What suggests that the mass of our Galaxy extends farther than its visible disk? 21-cm maps of the spiral arms The rotation curve of the outer edges of the Galaxy Orbits of open clusters in the disk Infrared observations of new star-forming regions X-ray images of other galaxies Answer: b © 2017 Pearson Education, Inc.

Question 10 What suggests that the mass of our Galaxy extends farther than its visible disk? 21-cm maps of the spiral arms The rotation curve of the outer edges of the Galaxy Orbits of open clusters in the disk Infrared observations of new star-forming regions X-ray images of other galaxies Explanation: The outer edges of the Galaxy’s disk rotate much faster than they should. Most of the mass of the Galaxy must be dark matter. © 2017 Pearson Education, Inc.