Test Bank Answers Ch10 Measuring the Stars - Understanding Our Universe 3e Complete Test Bank by Stacy Palen. DOCX document preview.
Chapter 10: Measuring the Stars
LEARNING OBJECTIVES
10.1 The Luminosity of a Star Can Be Found from the Brightness and the Distance
10.1a Understand parallax.
10.1b Distinguish among degrees, arcminutes, and arcseconds.
10.1c Explain why brightness depends on distance and luminosity.
10.1d Distinguish between apparent and absolute magnitudes.
10.2 Radiation Tells Us the Temperature, Size, and Composition of Stars
10.2a Recall Wien’s Law.
10.2b Explain the processes of atomic absorption and emission of light.
10.2c Describe the physical environments in which one would see blackbody radiation, emission lines, and absorption lines.
10.2d Use the blackbody nature of stars to relate luminosity, temperature, and size.
10.2e List the spectral types of stars in order of decreasing temperature.
10.2f Explain why stars of different temperatures have different spectral signatures.
10.2g Summarize what physical properties or characteristics of a star can be deduced from its spectral lines.
10.3 The Mass of a Star Can Be Determined in Some Binary Systems
10.3a Use Kepler’s laws to determine the masses of binary stars.
10.3b Differentiate between the observational information and methods used to determine stellar masses in visual binaries, eclipsing binaries, and spectroscopic binaries.
10.4 The H-R Diagram Is the Key to Understanding Stars
10.4a Compare the temperature, luminosity, spectral type, color, and size of stars at different positions on the H-R diagram.
10.4b Use a star position in the H-R diagram to determine its luminosity, surface temperature, size, mass, and spectral characteristics.
Working It Out 10.1
Working It Out 10.1a Calculate the distance to a star using its parallax.
Chapter 10: Measuring the Stars
MULTIPLE CHOICE
1. To measure the parallax of a star, astronomers would mark its position with respect to other stars in the field, on two distinct observations, separated by a timeline of
a. 6 hours. c. 6 months.
b. 12 hours. d. 12 months.
2. Parallax is used to directly measure
a. mass. c. luminosity.
b. brightness. d. distance.
3. How many arcseconds are there in a degree?
a. 60 c. 3,600
b. 360 d. 6,000
4. The star named Capella has an apparent magnitude of 0, whereas the star named Polaris has an apparent magnitude of 2, which means that Capella appears __________ Polaris in the night sky.
a. brighter than c. dimmer than
b. as bright as
5. What is the difference between brightness and luminosity?
a. These are different names for the same property.
b. Luminosity is how bright the star appears to us; brightness is how much light it emits.
c. Brightness is how bright the star appears to us; luminosity is how much light it emits.
d. Luminosity measures size; brightness measures temperature.
6. How is the distance to a star related to its parallax? Distance is
a. directly proportional to parallax.
b. inversely proportional to parallax.
c. directly proportional to parallax squared.
d. inversely proportional to parallax squared.
7. Which star in the following figure is closest to Earth?
a. star A c. The two stars are the same distance.
b. star B d. not enough information
8. At what distance is a star if it has a parallax of 1 arcsecond?
a. 1.00 astronomical unit (AU) c. 1.00 light-year
b. 3.26 AU d. 3.26 light-years
9. What unit is defined as the distance a star has with a parallax of 1 arcsecond?
a. degree c. light-year
b. astronomical unit d. parsec (pc)
10. Which of the following is equivalent to 1 parsec (pc)?
a. 3600 arcseconds (arcsec) c. 1.00 light-year
b. 3.26 AU d. 3.26 light-years
11. Stars A and B appear equally bright, but star A is half as far away from us as star B. Which of the following is true?
a. Star A is a fourth as luminous as star B.
b. Star A is half as luminous as star B.
c. Star B a fourth as luminous as star A.
d. Star B is half as luminous as star B.
12. Two stars have the same luminosity. If star A is four times brighter than star B, then
a. star B is two times farther away than star A.
b. star B is four times farther away than star A.
c. star B and star A lie at the same distance from us.
d. It is impossible to determine their relative distances from the information given.
13. State the uncertainty (in arcseconds) for parallaxes measured by the Hipparcos satellite.
a. .001 c. .1
b. .01 d. 1.0
14. The uncertainty for parallaxes measured by the Hipparcos satellite is 0.001 arcsec. What would be the range of distances for a star with a parallax of 1.235 arcsec as measured by Hipparcos?
a. 0.809–0.810 arcsec c. 1.234–1.236 arcsec
b. 0.809–0.810 pc d. 1.234–1.236 pc
15. Which of the following would decrease if a particular star was closer to Earth?
a. parallax c. absolute magnitude
b. apparent magnitude d. brightness
16. What is required to determine the luminosity of a star?
a. only distance c. both distance and brightness
b. only brightness d. only parallax
17. If a star’s measured parallax is 0.1 arcsec, what is its distance?
a. 1 pc c. 10 pc
b. 5 pc d. 50 pc
18. If a star’s distance is 100 pc, what is its parallax?
a. 0.01 arcsec c. 0.1 arcsec
b. 0.05 arcsec d. 0.5 arcsec
19. When an electron moves from a higher energy level in an atom to a lower energy level,
a. the atom is ionized.
b. a continuous spectrum is emitted.
c. a specific frequency of photon is emitted.
d. a specific frequency of photon is absorbed.
20. Star A is a blue star. Star B is a red star. Which is hotter?
a. star A
b. star B
c. We also need to know the luminosities of the stars to determine their temperatures.
d. Color is not related to temperature at all.
21. The spectral class of a star is related to its
a. luminosity. c. radius.
b. temperature. d. mass.
22. What spectral class is the Sun?
a. A0 c. F5
b. G2 d. M3
23. Stars are made mostly of
a. helium. c. hydrogen.
b. oxygen. d. nitrogen.
24. In the quantum mechanical view of the atom, an electron is best thought of as
a. a cloud that is centered on the nucleus.
b. a pointlike particle orbiting the nucleus.
c. free to orbit at any distance from the nucleus.
d. All of the above are true.
25. Stars generally exhibit
a. an absorption spectrum. c. an emission spectrum.
b. a continuous spectrum. d. both emission and absorption spectra.
26. Which sequence correctly lists the spectral classes of stars in order of decreasing temperature (from hottest to coolest)?
a. A B F G K M O c. A F O B M G K
b. O A B G F M K d. O B A F G K M
27. The spectrum in the following figure is
a. an absorption spectrum. c. a thermal spectrum.
b. an emission spectrum. d. not any of these types.
28. Stars of similar temperatures but different sizes will have
a. similar luminosities but different masses.
b. similar masses but different distances.
c. different spectral types but similar luminosities.
d. similar spectral types but different luminosities.
29. Why do O- and B-type stars have weaker hydrogen absorption lines than A-type stars?
a. O- and B-type stars are cooler than A-type stars.
b. A larger fraction of the surface hydrogen atoms in O- and B-type stars is ionized.
c. O- and B-type stars have converted much more of their hydrogen into heavier elements.
d. A-type stars have a higher mass than O- and B-type stars, and they have more hydrogen.
30. Eclipsing binary systems
a. orbit in the plane of the sky.
b. exhibit large radial velocity shifts.
c. contain equal mass stars.
d. contain stars that pass in front of one another during their orbit.
31. Applying Kepler’s third law to a binary star system allows us to determine
a. the mass of each star. c. the system’s distance.
b. the system’s total mass. d. the system’s brightness.
32. The slower-moving star in a binary is
a. the less massive star. c. the hotter star.
b. the more massive star. d. the more distant of the two stars.
33. All of the following are useful in determining the masses of stars in a binary system except:
a. the period of the orbits of the two stars.
b. the average separation between the two stars.
c. the luminosities of the two stars.
d. the velocities of the two stars.
34. In a binary star system that contains stars with 10 M and 5 M, the velocity of the 10 M star will be __________ times the velocity of the 5 M star.
a. 0.2 c. 1
b. 0.5 d. 2
35. You discover a binary star system in which star A has a velocity of 10 kilometers per second (km/s) and star B has a velocity of 30 km/s. Which one of the following mass combinations is physically possible?
a. Star A is 3 M, and star B is 1 M. c. Star A is 1 M, and star B is 3 M.
b. Star A is 1 M, and star B is 0.3 M. d. Star A is 2 M, and star B is 0.5 M.
36. Stars X and Y are 5 AU apart from each other. Star X is four times as massive as star Y. The center of mass of this system is __________ AU away from star X and __________ AU away from star Y.
a. 1; 4 c. 3; 2
b. 2; 3 d. 4; 1
37. The Hertzsprung-Russell (H-R) diagram (see the following figure) is a graph of
a. mass versus brightness for stars.
b. size versus mass for stars.
c. luminosity versus surface temperature for stars.
d. mass versus spectral type for stars.
38. Which of the following properties is never plotted on the horizontal axis of an H-R diagram?
a. color c. temperature
b. luminosity d. spectral class
39. Which of the following properties is plotted on the vertical axis of an H-R diagram?
a. color c. temperature
b. luminosity d. spectral class
40. The one property of a main-sequence star that determines all its other properties is its
a. luminosity. c. temperature.
b. mass. d. spectral type.
41. The stars that have the largest radii are classified as
a. giants. c. supergiants.
b. ultragiants. d. dwarfs.
42. The luminosity class of a star is related to its
a. distance. c. radius.
b. temperature. d. mass.
43. Examine the following figure. On a typical H-R diagram, where are main-sequence stars that have the coolest surface temperatures located?
a. in the upper left corner c. in the lower left corner
b. in the upper right corner d. in the lower right corner
44. On a typical H-R diagram, where are the largest stars located?
a. in the upper left corner c. in the lower left corner
b. in the upper right corner d. in the lower right corner
45. Examine the following figure. On a typical H-R diagram, where are main-sequence stars that have the hottest surface temperatures located?
a. in the upper left corner c. in the lower left corner
b. in the upper right corner d. in the lower right corner
46. Roughly what percentage of stars are main-sequence stars?
a. 10 percent c. 60 percent
b. 40 percent d. 90 percent
47. Examine the following figure. On a typical H-R diagram, what are the stars that have the hottest surface temperatures and the smallest radii?
a. red giants c. red dwarfs
b. blue giants d. white dwarfs
48. Using the following figure, determine the approximate temperature and absolute magnitude of the Sun.
a. 6000 kelvin (K); 
5 c. 6000 K; 1
b. 5; 6000 K d. 1; 6000 K
49. A star classified as a K0III star is
a. a giant that is cooler than the Sun.
b. a supergiant that is hotter than the Sun.
c. a main-sequence star that is hotter than the Sun.
d. a subgiant that is cooler than the Sun.
1. How is the unit of length known as a parsec defined?
2. Describe how brightness, luminosity, and distance are related.
3. The Sun’s apparent magnitude is about 
27, whereas its absolute magnitude is almost 5. Explain the difference.
4. A star with a stellar parallax of 0.035 arcsec is at a distance of how many parsecs?
5. In what ways are energy states of an atom like books occupying shelves in a bookcase?
6. How are atoms excited, and why do they decay?
7. How do astronomers use spectra to determine the composition of a star?
8. What are the two main chemical elements that make up the Sun? How much of the mass of the Sun is composed of elements other than these two?
9. What is the spectral type of stars that have the strongest hydrogen absorption lines? Why do stars that are hotter than these have weaker hydrogen lines?
10. Why do we see black lines in an absorption spectrum if the absorbed photons are (almost) instantaneously reemitted by the atoms in the cloud?
11. If given the image alone in the following figure, what further information might be required to determine that the stars are a visual binary system?
12. Using information from the following figure, explain why star 2 is the more massive star of the eclipsing binary pair.
13. You observe a binary star system and find that star 1 has a velocity of 10 meters per second (m/s) and star 2 has a velocity of 40 m/s. What is the ratio of masses of the two stars (M1M2)?
14. You observe a binary star system and find that star 1 has a velocity of 20 m/s and star 2 has a velocity of 40 m/s. What is the ratio of masses of the two stars (M1M2)? If star 2 has a mass of 2 solar masses, what is the mass of star 1?
15. What information is needed to determine the mass of each star in a binary system? Explain how this information is obtained and used.
16. What is the main property of a main-sequence star that determines nearly all its other properties?
17. Describe the luminosity classes found on the following H-R diagram.
18. Define and distinguish the numbers on the left and right vertical axis of the following H-R diagram.
19. Explain how we can use spectroscopic parallax to determine the distance to a star farther away than a few hundred light-years.
20. Examine the following figure. Along the main sequence, how do the luminosity, temperature, radius, and mass of stars change as you go from the upper left to the lower right corners of the H-R diagram?
