ASTRONOMY 123
Exam I
Answers
1. The Milky Way is which type of galaxy?
b. SBb or SBc
2. A quasar with a red shift of 2 would be at which of the following look-back times?
d. 10,000,000,000 years
3. The spectrum of light coming from normal galaxies is characterized by
b. the sum of many blackbody spectra
4. Quasars have the following properties, except ______________
---> a. visible to the naked eye
b. large redshift
c. variable luminosity
d. star-like appearance
5. The center of the Milky Way galaxy
a. is located in the direction of the constellation Sagittarius
b. is the site of intense matter/anti-matter annihilation
c. contains many closely packed stars
d. is believed by many astronomers to be the location of a
giant black hole
---> e. all of the above
6. Star formation primarily occurs in the Milky Way Galaxy's
c. disk
7. The globular clusters of the galaxy are located primarily in the
b. halo of the galaxy
8. How do we know that about 90% of the matter in galaxies has not been
observed.
a. From the galactic rotation curves
9. A galaxy is
d. a huge collection of stellar and interstellar matter
isolated in space and bound together by its own gravity
10. The Sun's orbit around the center of the galaxy
b. lies in the plane of the galaxy's disk
11. When the globular clusters were formed, the Milky Way was
a. a large sphere of at least 100,000 light years diameter
12. Which galaxy type contains little gas or dust?
c. elliptical
13. What do we call a galaxy that emits much more energy, especially as radio
waves, than a normal galaxy?
c. active galaxy
14. The period of revolution of the Sun around the Milky Way Galaxy is about
d. 225 million years
15. The Doppler effect predicts that objects moving toward us will
d. appear bluer
16. Galactic (open) clusters are found mainly
b. within the spiral arms of the galaxy
17. The distance to the Andromeda Galaxy is about
d. 2,000,000 light years
(we now know if it more like 2,500,000 light years
but 2,000,000 light years is the best answer here)
18. Rich clusters of galaxies
a. contain hundreds to thousands of galaxies
19. The globular clusters are
d. clusters of many old stars
20. The kind of stars most useful in determining distances within the
local group of galaxies are:
d. variable stars (like Cepheids)
21. The mass of the Milky Way Galaxy, in units of solar mass, is nearest to
d. 10^12
22. A general rule of stars is
d. the lower the metal abundance, the farther objects appear
from the galactic disk
23. The density of material within a spiral arm of a spiral galaxy is
a. higher than between the arms
24. Astrophysicists have tried to explain spiral arm formation with
a. the density wave theory
c. the supernova chain reaction theory
---> d. both a and c
25. The first determination of the Sun's position in the galaxy was done
(by Shapley) from
c. using the locations of globular clusters in the sky
26. The number of stars in the Milky Way Galaxy is thought to be nearest to
d. 10^12
(this is a typo on the exam. A better answer would be
10^11, but that's closest to 10^12 among the choices)
27. The main difference between an Sa galaxy and an Sc galaxy is
d. the Sa galaxy has a larger central bulge
28. Which of the following is one way of expressing Hubble's Law?
a. The greater the distance to a galaxy, the greater its recessional
velocity.
29. What does the Hubble Law measure?
a. The rate of expansion of the universe.
30. The most distant observed galaxies in the universe have look-back times
of about__________ years.
c. 13 billion
31. Which of the following stars generally have the smallest metal (or
heavy element) contents?
c. Population II stars
32. Hubble established that the Andromeda Galaxy is outside the Milky Way
when he measured
a. Cepheid variable stars
33. The Magellanic Clouds are
d. irregular galaxies
34. Spiral arms appear prominently in the images of spiral galaxies because
c. hot stars in the disk are distributed in a spiral pattern while
the cool stars are spread more uniformly
35. What property, or properties, is (are) common to all spiral galaxies?
a. Ongoing star formation
b. The disk, the bulge, and the halo
c. Abundant interstellar gas
---> d. all of the above
36. Most of the energy emitted by radio galaxies is emitted in the radio
and _______ parts of the electromagnetic spectrum
a. infrared
37. The variations in a Seyfert galaxy's luminosity over a year or so shows
its region of emission is
a. not very large
38. Variable stars are useful as standard candles because of the close
relationship between
a. period of pulsation and luminosity
39. What was the subject of the famous Shapley-Curtis debate?
d. The nature and distance of spiral nebulae
40. The galaxies near the Milky Way consist of
a. about 50 galaxies, including 3 spiral galaxies
41. What leads us to conclude quasars are relatively small
a. rapid variability of radiation output
42. The distance to quasars is determined by
b. measuring the redshift of emission lines
43. When charged particles accelerate they
d. emit synchrotron radiation
44. Identify M31 from the following list
d. The Andromeda Galaxy
45. What two kinds of objects are considered as possibly making up at
least part of the dark matter?
a. low-mass stars and exotic subatomic particles
46. Which type of galaxy is characterized by little gas or dust, no O or B type stars,
and being reddish in color?
a. elliptical
47. The look-back times for quasars are
c. very large
48. Which of the following is NOT a part of the central engine of an active
galaxy
---> a. globular cluster
b. supermassive black hole
c. accretion disk
d. jets of high speed particles
49. The largest objects seen in the universe are
a. radio galaxies
50. The most likely sources of energy in Active Galaxies are
c. supermassive black holes
51. Seyfert galaxies are characterized by
b. bright nuclei
52. A small cluster of galaxies of which the Milky Way is a member is the
a. Local Group
53. The rotation curve of our galaxy supports the thesis that
c. about 90% of the mass of our galaxy is dark matter
54. Which of the following is an important clue about the evolution of the Milky Way?
d. the distribution of Population II stars
55. In a lobe radio galaxy, the radio emission primarily comes from
c. enormous extensions of the galaxy that dwarf the optical galaxy
56. Which of the following elements are NOT required for synchrotron radiation
---> a. Cepheid variables
b. charged particles
c. magnetic field
d. motion of the particles
57. Which of the following characteristics is common to spiral galaxies?
c. young stars in the disk
58. The most circular elliptical galaxy is:
c. E0
59. Galaxies which appear like normal spirals, but with a very bright
galactic center.
a. Seyfert galaxies
60. The mass of the black hole responsible for energy production in the
active galaxy M87 is thought to be approximately _________.
d. 3 billion solar masses
61. Quasars, in visible light, have a ____________ appearance.
d. star-like
62. The most distant quasars have
c. the largest redshifts
SHORT ANSWER QUESTIONS
1. What form of radiation is emitted by accelerating charged
particles and is thought to be the source of nonthermal
radiation from active galaxies?
Synchrotron Radiation
2. Calculate the distance that light travels in 1 year in kilometers.
That is, how big is a light-year in kilometers?
300,000 km/sec x 60 sec/min x 60 min/hr x 24 hr/day x 365 day/yr x 1 yr
= 9.5 x 1012 km
3. What is the name of the effect that causes the color of a moving object to be
shifted to red or blue?
Doppler effect
4. What is the oldest type of star cluster?
Globular cluster
5. What type of galaxy is the most common?
Irregular galaxy
6. What type of active galaxy is M87?
Radio galaxy
7. Given that the light from the Sun peaks at 0.5 microns,
at what wavelength would the light from a Sunlike star peak, if it were
receding from Earth with a redshift of 4? (Show the math)
Redshift = (obs wavelength - true wavelength)/true wavelength = 4
(obs. wavelength - 0.5 microns)/0.5 microns = 4
obs wavelength - 0.5 microns = 2 microns
obs wavelength = 2.5 microns
8. Suppose the shift in the spectrum of a distant galaxy is
measured, and the line normally located at 0.5 microns
has shifted to 0.75 microns. Calculate the redshift
of this galaxy. (Show the math)
Redshift = (obs wavelength - true wavelength)/true wavelength
= (0.75 microns - 0.5 microns)/0.5 microns = 0.5