Activity 25: RR Lyrae Stars and the Distance to the Center of the Galaxy ©2014 W. W. Norton & Company, Inc. 15 Post-25.1: What aspect about globular clusters and our observations of the distances to them modified our view of the Milky Way Galaxy and our place in it? a. They all orbit the center of the galaxy, and the center of their distribution is not where we are. b. Some of the globular clusters are very far away and must belong to the Andromeda Galaxy. c. We found out that there are hundreds of globular clusters hidden by columns of dust. d. The most distant globular clusters are metal-rich and so must have originated in the disk. ©2014 W. W. Norton & Company, Inc. 16 Post-25.1: What aspect about globular clusters and our observations of the distances to them modified our view of the Milky Way Galaxy and our place in it? a. They all orbit the center of the galaxy, and the center of their distribution is not where we are. b. Some of the globular clusters are very far away and must belong to the Andromeda Galaxy. c. We found out that there are hundreds of globular clusters hidden by columns of dust. d. The most distant globular clusters are metal-rich and so must have originated in the disk. ©2014 W. W. Norton & Company, Inc. 17 Post-25.2: Astronomers need to measure the distances to the stars in the Milky Way globular clusters. What method should they use to find the distances? a. Measure the trigonometric parallaxes of all the globular clusters during the course of a year. b. Count the number of O- and B-type stars and remnants of supernovae in the clusters. c. Look for flickering X-rays coming from black holes in binary systems in the clusters. d. Find RR Lyrae variable stars in the clusters and measure their mean apparent magnitudes. ©2014 W. W. Norton & Company, Inc. 18 Post-25.2: Astronomers need to measure the distances to the stars in the Milky Way globular clusters. What method should they use to find the distances? a. Measure the trigonometric parallaxes of all the globular clusters during the course of a year. b. Count the number of O- and B-type stars and remnants of supernovae in the clusters. c. Look for flickering X-rays coming from black holes in binary systems in the clusters. d. Find RR Lyrae variable stars in the clusters and measure their mean apparent magnitudes. ©2014 W. W. Norton & Company, Inc. 19 Post-25.3: Why are globular clusters ideal for determining the size of the Milky Way and our location in the galaxy? a. Most lie above the plane of the Milky Way and so are not very obscured by dust. b. Most globular clusters have a large number of RR Lyrae variable stars. c. The clusters must orbit the center of the galaxy. d. All of these answers are correct. ©2014 W. W. Norton & Company, Inc. 20 Post-25.3: Why are globular clusters ideal for determining the size of the Milky Way and our location in the galaxy? a. Most lie above the plane of the Milky Way and so are not very obscured by dust. b. Most globular clusters have a large number of RR Lyrae variable stars. c. The clusters must orbit the center of the galaxy. d. All of these answers are correct. ©2014 W. W. Norton & Company, Inc. 21 Post-25.4: An observer far outside our galaxy would best describe our galaxy and the Sun's position in it as a a. disk of stars with our Solar System toward the edge. b. disk of stars centered on our Solar System. c. disk of stars with our Solar System located in the bulge. d. sphere of stars centered on our Solar System. ©2014 W. W. Norton & Company, Inc. 22 Post-25.4: An observer far outside our galaxy would best describe our galaxy and the Sun's position in it as a a. disk of stars with our Solar System toward the edge. b. disk of stars centered on our Solar System. c. disk of stars with our Solar System located in the bulge. d. sphere of stars centered on our Solar System. ©2014 W. W. Norton & Company, Inc. 23 This concludes Activity 25: RR Lyrae Stars and the Distance to the Center of the Galaxy ©2014 W. W. Norton & Company, Inc. 24.