Stars and Galaxies Review Choose the best response. Write the letter of that choice in the space provided. 1. In the majority of stars, the most common element is a. oxygen. b. helium. c. hydrogen. d. sodium. 2. The color of the hottest stars is a. red. b. yellow. c. green. d. blue. 3. Stars appear to move in circular paths around Polaris because a. the earth rotates on its axis. b. the earth orbits the sun. c. the stars revolve around Polaris. d. Polaris is the center of the Milky Way Galaxy. 4. The change in position of a nearby star compared with the position of a faraway star is called a. parallax. b. red shift. c. blue shift. d. a Cepheid variable. 5. The brightest stars have apparent magnitudes that are a. over +20. b. between +10 and +19. c. between +1 and +9. d. negative numbers. 6. The absolute magnitude of a star is a. the relative brightness of the star. b. the true brightness of the star. c. the comparative brightness of the star. d. the apparent brightness of the star. 7. A protostar becomes a star when it begins to a. develop a red shift. b. generate energy. c. shrink and spin. d. explode as a nova. 8. A main-sequence star generates energy by fusing a. nitrogen into iron. b. helium into carbon. c. hydrogen into helium. d. nitrogen into carbon. Study Guide 105
Choose the best response. Write the letter of that choice in the space provided. 9. A dying star can shed some of its gases as a a. planetary nebula. b. white dwarf. c. globular cluster. d. supernova. 10. Black holes are difficult to locate because they a. move very quickly. b. do not give off light. c. have very low gravity. d. are far away from any stars. 11. A pattern of stars is called a a. galaxy. b. nebula. c. pulsar. d. constellation. 12. Stars appear in fixed locations in the sky because they a. are so far from the earth. b. do not move. c. are all moving toward the earth. d. are all in the same galaxy. 13. The basic types of galaxies are a. spiral, elliptical, and irregular. b. barred, elliptical, and open. c. spiral, quasar, and pulsar. d. open, binary, and globular. 14. Quasar formation is associated with a. nuclear fusion. b. main-sequence stars. c. the explosion of a supernova. d. the early universe. Critical Thinking 1. If the spectrum of a star indicates that the star shines with a red light, approximately what is the surface temperature of the star? 106 Study Guide
2. Why are different constellations visible during different seasons of the year? 3. Explain why Polaris is considered to be a very bright star even though it is not a bright star in the earth s sky. 4. Why does heat build up more rapidly in a massive protostar than in a less massive one? 5. Explain why an old main-sequence star will be composed of a higher percentage of helium than will a young main-sequence star. Study Guide 107
6. If all galaxies began to show blue shifts, what would this indicate about the fate of the universe? Application 1. If you determined that a certain star displayed a large parallax, what could you say about its distance from the earth? 2. Suppose that a scientist has discovered a red-dwarf star. Describe the likely size and surface temperature of such a star. 3. When looking through a nearby university s telescope, you observed a galaxy that has no young stars and contains little dust or gas. What kind of galaxy were you probably looking at? 108 Study Guide
Page 560: Discussion (Reinforcement) To help students understand how astronomers can infer the existence of black holes, use the example of two ice skaters holding hands and spinning in a circle. If one of the skaters were invisible, an observer could still infer that two skaters were present by observing the effect the invisible skater would have on the motion of the visible skater. Similarly, astronomers detect black holes by their gravitational effects on nearby stars, gas, or dust. Page 565: EarthBeat You may wish to explain that some quasars appear to be moving away from the earth at 80 percent of the speed of light. Have students calculate this speed (300,000 km/s 0.80 = 240,000 km/s). Small-Scale Investigation Parallax (p. 551) Science Process Skills: observing, interpreting, inferring Answers to Analysis and Conclusions 1. The plate does not actually change position, although it does appear to move when it is viewed from different locations. 2. The apparent change in position of the plate is greater at short distances than it is farther away because the angle formed by the observer s new line of sight and previous line of sight to the red plate decreases with distance. 3. Answers will vary. A typical answer would be that the stars exhibit an apparent motion over a period of months that is similar to the apparent motion of the red plate in this investigation. In the case of the stars, the change in the observer s location is the result of the earth s orbit around the sun. Review Answers to Review 1. c 5. d 9. d 13. a 2. d 6. b 10. b 14. d 3. a 7. b 11. d 4. a 8. c 12. a Answers to Critical Thinking 1. about 3,000 C 2. During each season of the year as the earth revolves around the sun, some constellations are obscured by the sun. 3. Polaris gives off a lot of light but is very distant from the earth. 4. A massive protostar will have more bits of matter that increase its pressure. This increased pressure causes the temperature of the protostar to rise. 5. A main-sequence star converts hydrogen into helium. 6. that it was decreasing Answers to Application 1. The star is relatively near the earth. 2. It would be small and cool. 3. elliptical In-Depth Investigation Star Magnitudes (pp. 568 569) Approximate time: 1 class period Objectives: to determine the effect of distance on brightness and the relationship between temperature and color Skills: observing, measuring, calculating, predicting Prelab Discussion Before students begin this investigation, you may want to review squaring numbers. Ask students to explain the difference between absolute magnitude and apparent magnitude. Students should be able to explain why stars that appear to have equal brightness are not always the same distance from the earth. Also discuss with students the reason the flame of a candle ranges from blue, at the center of the flame, to white-yellow, and then orange at the edges. (The flame is hottest at the center, around the burning wick.) Teaching Strategies 1. Because of the amount of equipment used in this investigation, have students work in groups of two or three. 2. To prepare the wire to be used by the students, use a pair of electrician s wire strippers. If they are unavailable, use a single-edged razor blade or mat knife to cut the wires to the proper lengths, T132