Stellar Brightness, Distances, and Motions

1. Pluto is about 14^th magnitude at most. How many times fainter is it than Venus, which can surpass magnitude -4?

a. 4 magnitudes

b. 9 magnitudes

c. 10 magnitudes

d. 15 magnitudes

e. None of these.*

2. Why is it that planets change in apparent brightness?

a. They do not have a constant energy output.

b. Sunlight reflected from them changes with time.

c. Most of them have variable albedos.

d. Their distances from the sun and from the earth change drastically with time.*

e. None of these.

3. We cannot tell merely by looking in the sky that stars in a given constellation are at different distances, while in a room we can easily tell that objects are at different distances from us. What is the difference between the two situations?

a. Our brain cannot interpret small parallax angles as a third dimension.

b. The stars are so far away that they do not exhibit parallax discernible by our eyes.

c. In a room, the separation of our eyes is large enough with respect to the distance to an object that we can see a parallax and translate it to a third dimension.

d. All of the above.*

e. None of the above.

4. Would the parallax of a nearby star be larger or smaller than the parallax of a more distant star?

a. Smaller.

b. The same.

c. Larger.*

d. Parallax cannot be observed.

e. None of these.

5. A star has an observed parallax of 0.2 arc second. Another star has a parallax of 0.02 arc sec. How much farther away is it?

a. 10 times.*

b. 100 times.

c. 1000 times.

d. 10000 times.

e. none of these.

6. What is the significance of the existence of the main sequence?

a. For a large class of stars, temperature and radius have a simple relation.

b. For a large class of stars, mass and radius have a simple relation.

c. For a large class of stars, mass and temperature have a simple relation.

d. For a large class of stars, temperature and luminosity have a simple relation.*

e. None of these.

7. What is the observational difference between a dwarf and a white dwarf?

a. The only difference is color.

b. A dwarf is an ordinary main-sequence star and a white dwarf is an electron degenerate star.*

c. A dwarf is an ordinary main-sequence star and a white dwarf is a neutron degenerate star.

d. A dwarf is an ordinary main-sequence star and a white dwarf is a proto-star.

e. None of these.

8. Two stars have the same apparent magnitude and are the same spectral type. One is twice as far away as the other. What is the relative size of the two stars?

a. The nearer star is a fourth the size of the farther star.

b. The nearer star is half the size of the farther star.*

c. The nearer star is twice the size of the farther star.

d. The nearer star is a four times the size of the farther star.

9. The position of a star may be measured relative to another star to a precision of _______seconds of arc.

a. 100

b. 10

c. 1

d. 0.1

e. 0.01.*

10. The determination of stellar parallax is important because it allows the direct determination of

a. mass

b. distance*

c. diameter

d. velocity

e. all the above.

11. The distance to the nearest star (other than the Sun) is closest to __________ parsec(s).

a. 0.01

b. 0.1

c. 1*

d. 10

e. 100

12. The most distant star for which an accurate stellar parallax can be measured is about

a. 10 parsecs

b. 100 parsecs*

c. 100,000 parsecs

d. 1,000,000 parsecs

e. limitless.

13. The apparent visual magnitude of one star is three magnitudes greater than for another star. Therefore, the first star is approximately _________ than the second star?

a. three times brighter

b. three times fainter

c. six times brighter

d. 16 times brighter.

e. 16 times fainter.*

14. If on a certain day the Sun has an apparent visual magnitude of -26.5, while in the evening the moon has an apparent magnitude of -12.5, how much brighter did the Sun appear on that day?

a. 10 times

b. 100 times

c. 1,000 times

d. 10,000 times

e. 1,000,000 times*

15. Which one of the following is the primary difference between the observed spectra of most stars?

a. the presence or absence of a continuous spectrum

b. the differing strengths and patterns of the absorption lines*

c. the differing strengths and patterns of the emission lines

d. spectra of all stars have approximately the same appearance.

16. The observed differences between stellar spectra are caused primarily by differences in stellar

a. luminosity

b. chemical composition

c. temperature*

d. motions

e. location in space.

17. If a stellar spectrum shows strong lines produced by ionized helium the spectral type of the star is

a. O*

b. B

c. A

d. F

e. M.

18. If the spectrum of some object has spectral lines of helium and strong lines from metals, the object is probably

a. nonexistent

b. a star whose temperature varies with time

c. a star with strong emission lines

d. a binary star system.*

19. If a star is surrounded by a shell of hot gas, the spectrum of this hot gas will be a (an) ________ spectrum.

a. continuous

b. emission line*

c. absorption line.

20. What percentage of stars in the sky are thought to be members of binary systems?

a. 10

b. 30

c. 50*

d. 75

e. 95.

21. Luminosity is

a. energy per second per unit area in the visual region

b. energy per second per unit area over all wavelengths

c. a different word for magnitude

d. total energy per second radiated over all wavelengths.*

22. A star's luminosity depends only on the star's

a. distance and diameter.

b. temperature and distance.

c. distance.

d. temperature and diameter. *

e. apparent magnitude.

23. Absolute visual magnitude is

a. the apparent magnitude of a star observed from Earth.

b. the luminosity of a star observed from a distance of 1000 pc.

c. the apparent magnitude of a star observed from a distance of 10 pc. *

d. the luminosity of a star observed from Earth.

e. c and d

24. The reason astronomers use the concept of the absolute magnitude is to

a. make life difficult for introductory astronomy students!

b. allow stars to be compared with the effects of differing distance removed*

c. allow stars to be compared with the effects of differing mass removed

d. allow stars to be compared with the effects of differing temperature removed

e. allow stars to be compared with the effects of differing radius removed.

25. Which of the following is not in itself useful for determining stellar temperature?

a. spectral class

b. color index

c. absolute magnitude*

d. degree of ionization

e. wavelength of maximum intensity of the underlying spectrum.

26. The methods of temperature determination we have discussed give us the temperature of the

a. photosphere*

b. region just below the photosphere

c. point half-way to the center

d. center

e. corona.

27. Stellar surface temperatures range from

a. 5,000-6,000 K

b. 4,000-10,000 K

c. 3,000-20,000 K

d. 2,000-50,000 K*

e. 100-100,000 K

28. An H-R diagram is a plot of

a. heat, versus radius

b. luminosity versus radius

c. mass versus temperature

d. luminosity versus temperature*

e. mass versus luminosity.

29. On the H-R diagram, 90 percent of all stars are

a. in the giant region.

b. in the supergiant region.

c. among the B stars.

d. among the G stars.

e. on the main sequence. *

30. The main sequence extends from

a. high luminosity, high temperature to low luminosity, low temperature*

b. high luminosity, low temperature to low luminosity, low temperature

c. high luminosity, low temperature to low luminosity, high temperature

d. high luminosity, high temperature to low luminosity high temperature.

31. We know that giant stars are larger in diameter than the sun because

a. they are more luminous but have about the same temperature. *

b. they are less luminous but have about the same temperature.

c. they are hotter but have about the same luminosity.

d. they are cooler but have about the same luminosity.

e. they have a larger absolute magnitude than the sun.

32. Red supergiant stars are in what part of the H-R diagram?

a. high luminosity, high temperature

b. high luminosity, low temperature*

c. low luminosity, low temperature

d. low luminosity, high temperature.

33. The purpose of the spectroscopic parallax is to determine

a. distance*

b. temperature

c. apparent magnitude

d. bolometric magnitude

e. color index.

34. Whenever a star's absolute magnitude can be determined, its ___________ can also be determined if we have also observed the star's apparent magnitude.

a. temperature

b. mass

c. radius

d. distance*

e. spectral class.

35. The most fundamental of all stellar properties is the

a. radius

b. mass*

c. temperature

d. luminosity

e. chemical composition.

36. Stellar masses are most easily determined with use of

a. Newton's first law

b. Newton's second law as modified by Kepler

c. Kepler's second law

d. Kepler's third law as modified by Newton*

e. none of the above.

37. When we see the light from a distant galaxy, what kind of stars are we seeing mostly?

a. Low mass stars.

b. Medium mass stars.

c. High mass stars.*

d. Stars of all masses.

e. None of these.

38. The sun's spectrum peaks at 5600 Å. What wavelength is the peak of a star whose temperature is twice that of the sun?

a. 1867 Å

b. 2800 Å*

c. 11200 Å

d. 16800 Å

e. None of these.

39. Compare Planck curves for stars of spectral types O, G, and M.

a. The Planck curves for O stars are higher at all wavelengths and peak farther to the blue than do Planck curves for G stars; the relation of Planck curves for G stars and M stars is similar to that of O and G stars. *

b. The Planck curves for O stars are lower at all wavelengths and peak farther to the red than do Planck curves for G stars; the relation of Planck curves for G stars and M stars is similar to that of O and G stars.

c. The Planck curves for O stars are higher at all wavelengths and peak farther to the blue than do Planck curves for G stars; the Planck curves for G stars are lower at all wavelengths and peak farther to the red than do Planck curves for M stars.

d. The Planck curves for O stars are lower at all wavelengths and peak farther to the red than do Planck curves for G stars; the Planck curves for G stars are higher at all wavelengths and peak farther to the blue than do Planck curves for M stars.

e. None of these.

40. What main factor determines the spectral type of a star?

a. Core temperature.

b. Surface temperature.*

c. Atmospheric composition.

d. Radius.

e. None of these.

41. What spectral types have the strongest hydrogen absorption lines?

a. O

b. B and A.*

c. F and G.

d. K and M.

e. None of these.

42. In order to determine the distance to a star in kilometers by heliocentric (trigonometric) parallax, an astronomer must know

a. the Earth's diameter

b. the Earth-Sun distance *

c. the Earth-Moon distance

d. the angle between the Sun and the star

43. Star A appears bluish white in color, while star B appears reddish in color

a. star A is less luminous than star B

b. star A is hotter than star B *

c. star A is more luminous than star B

d. star A is cooler than star B

44. The mass-luminosity relation for main-sequence stars tells you that

a. the more massive stars are bigger

b. the more massive stars are more luminous *

c. the less massive stars are more luminous

d. the less massive stars are smaller

45. In order to find a star's density, we need to know its

a. mass

b. radius

c. luminosity

d. both a and b *

e. both b and c