1.	What important role do Cepheid variables stars have in astronomy?	
A)	Distance measurements to distant galaxies	
B)	The determination of stellar luminosities	
C)	The determination of speeds of stars in galactic arms from the Doppler shift of their spectra	
D)	The keeping of accurate time	

2.	Why are we able to see only a relatively small part of our Galaxy, the Milky Way Galaxy?	
A)	There are so many stars in our Galaxy that the more distant ones are hidden behind the nearer ones.	
B)	Distant stars are obscured by gas in interstellar space.	
C)	Expansion of the universe has carried the more distant stars out of our view.	
D)	Distant stars are obscured by dust in interstellar space.	

3.	The method used by Harlow Shapley in 1917 to estimate the Sun's location in our Galaxy was the measurement of	
A)	the locations of globular clusters around the Galaxy.	
B)	the density of stars in different directions along the Milky Way.	
C)	distances to open star clusters and H II regions in the disk of the Galaxy.	
D)	the structure of the Andromeda Galaxy and a comparison of this to the structure of our Galaxy.	

4.	When distances were carefully measured from the Earth to globular clusters above and below the Milky Way plane (where our view of them is not obscured by interstellar dust and gas), their distribution was found to be	
A)	spherically symmetric about a point in the constellation Sagittarius and concentrated in that direction.	
B)	in a relatively flat disk almost perpendicular to the plane of the Galaxy, with a relatively higher density of clusters toward its center.	
C)	concentrated in the plane of the Milky Way and clustered around the Sun's position, indicating that the Sun is close to the Galaxy's center.	
D)	uniformly distributed throughout space, with no concentration in any area of the Milky Way.	

5.	Radio waves of 21-cm wavelength originate from which component of the interstellar medium?	
A)	Cool, neutral atomic hydrogen	
B)	Cold, molecular hydrogen, H2	
C)	Cool, carbon monoxide, CO	
D)	Hot, ionized atomic hydrogen	

6.	Which type of radiation has been most effective in evaluating the spiral arm structure of our Galaxy?	
A)	21-cm radio emission from electron “spin-flip” transitions in cool hydrogen gas	
B)	Lyman  ultraviolet emission from hot hydrogen gas	
C)	Synchrotron radiation from electrons spiraling in magnetic fields within the spiral arms	
D)	Neutrinos from exploding stars in the spiral arms since they can penetrate dust and gas easily	

7.	What quantum transition occurs inside a hydrogen atom to produce a 21-cm radio photon?	
A)	An electron falls from the level n = 100 to the level n = 99 in the atom.	
B)	An electron in the ground atomic state reverses its direction of spin with respect to that of the proton.	
C)	An electron reverses the direction of its motion in orbit around the proton.	
D)	The electron combines with the proton in the nucleus to become a neutron, producing energy.	

8.	When we measure the narrow line emissions of hydrogen at 21-cm radio wavelengths along a particular line of sight through the disk of our Galaxy, we can tell the distances to different hydrogen clouds because	
A)	absorption of extragalactic radiation at this wavelength will be greater the farther away the absorber is from the Sun.	
B)	clouds that are farther away have smaller angular sizes.	
C)	the emission is weaker from clouds that are farther away.	
D)	clouds at different distances have different Doppler shifts because of the rotation of the Galaxy.	

9.	Which of the following components of the Galaxy best outline the spiral arms of the Galaxy?	
A)	Young O and B stars, dust, and gas	
B)	Globular clusters	
C)	Predominantly solar-type stars	
D)	White dwarf stars	

10.	When we look out into the plane of the Galaxy, how far can we see?	
A)	Infinitely far	
B)	About 100,000 ly	
C)	Less than 1000 ly	
D)	About 10,000 ly	

11.	The dimensions of the disk of our Milky Way Galaxy are	
A)	diameter 100,000 ly; thickness 2000 ly.	
B)	diameter 10,000 ly; thickness 28,000 ly.	
C)	diameter 2000 ly; thickness 100,000 ly.	
D)	diameter 28,000 ly; thickness 2000 ly.	

12.	Where is the solar system located in our Galaxy?	
A)	In the galactic disk	
B)	It is not in a galaxy but in the intergalactic space between galaxies.	
C)	In the galactic halo	
D)	In the galactic nucleus	

13.	What is the significance of the object Sagittarius A* (“Sagittarius A-star”) in our Galaxy?	
A)	It appears to be a jet of material ejected from an accretion disk around a supermassive black hole in the galactic nucleus.	
B)	It is a globular cluster passing close to the galactic nucleus, and the RR Lyrae stars in it allow the distance to the galactic center to be calculated.	
C)	It is a bright, high-speed cloud of gas close to the galactic nucleus that allows the mass of the nucleus to be calculated.	
D)	It appears to be the actual nucleus of the Galaxy.	

14.	What type of object has been proposed to explain the tremendous activity detected at the center of our Galaxy?	
A)	A giant molecular cloud	
B)	A supermassive black hole	
C)	A supernova explosion	
D)	A rapidly rotating neutron star	

15.	What evidence now exists for a supermassive black hole at the center of our Galaxy?	
A)	Very bright X-ray emissions from the galactic center	
B)	Observations of intense inflow of matter toward the center of the Galaxy as seen by light, Doppler-shifted toward the red, emitted by this matter	
C)	Very rapid motion of matter close to the nucleus of the Galaxy, requiring a very massive body to hold it in orbit	
D)	A very dark void in an otherwise bright region of space near the galactic center, indicating the presence of a black hole	

16.	Which of the following statements correctly describes the rotation of our Galaxy?	
A)	The disk rotates like a solid object (objects at all distances take the same time to complete an orbit), and the halo objects have random orbits with no net rotation of the halo about the center of the Galaxy.	
B)	Objects in the disk have random orbits with no net rotation of the disk about the center of the Galaxy, and the halo rotates differentially (objects farther from the center take longer to complete an orbit than objects closer to the center).	
C)	The disk rotates differentially (objects farther from the center take longer to complete an orbit than objects closer to the center), and the halo rotates differentially (objects farther from the center take longer to complete an orbit than objects closer to the center).	
D)	The disk rotates differentially (objects farther from the center take longer to complete an orbit than objects closer to the center), and the halo objects have random orbits with no net rotation of the halo about the center of the Galaxy.	

17.	The time for the Sun to orbit the galactic center once in its motion in the Galaxy is	
A)	28,000 years.	
B)	230 million years.	
C)	about 500,000 years.	
D)	2.3 million years.	

18.	How do we obtain an estimate of the amount of mass that is inside the Sun's orbital path in our Galaxy?	
A)	By counting stars, assuming an average stellar mass and calculating the total mass	
B)	By observing the bending of light from distant galaxies as this light passes near the Milky Way center	
C)	By observing the movement of the Galaxy toward neighboring galaxies because of mutual gravitational attraction	
D)	By applying Kepler's law to the motion of the Sun and other nearby stars	

19.	The present estimate for the total mass of our Galaxy in units of solar mass is about	
A)	2.3 × 108.	
B)	1012.	
C)	1.1 × 1011.	
D)	1066.	

20.	The presence of a very large amount of unseen (“dark”) matter in the halo of our Galaxy is deduced from	
A)	the rotation curve of our Galaxy, in which orbital speeds of stars appear to obey Kepler's law.	
B)	the rotation curve of our Galaxy, in which orbital speeds of stars in the outer regions of the Galaxy are significantly higher than is predicted by Kepler's law in which the value for the observed mass in the Galaxy is used.	
C)	the unexpected absence of luminous matter (stars, etc.) beyond a certain distance from the galactic center.	
D)	the high amount of interstellar absorption in certain directions.	

21.	What fraction of the mass of our Galaxy appears to be in the form of dark matter, which we cannot see but can detect through its gravitational influence?	
A)	About 50%	
B)	About 10%	
C)	0%—who ever heard of matter that can't be seen?	
D)	About 90%	

22.	What is microlensing?	
A)	The beaming of radiation by accretion disks	
B)	The use of small telescopes to enhance contrast by eliminating scattered light	
C)	The focusing of starlight by the gravitational fields of “small” objects like planets or brown dwarfs	
D)	The focusing of starlight by planetary atmospheres	

23.	In a recent survey of stars in the sky, it was found that occasionally a star that is normally of constant brightness will slowly brighten and then fade back to its original brightness again over the space of several weeks. What is believed to be the cause of this change in brightness?	
A)	A massive coronal ejection on a star with abnormally strong magnetic fields	
B)	The gradual motion of the star through a break or hole between interstellar dust clouds	
C)	Microlensing by compact objects such as brown dwarfs passing in front of the star	
D)	The “lighthouse beam” of a slowly rotating neutron star companion	

24.	What physical process has allowed astronomers to measure the overall number and distribution of brown dwarfs in our Galaxy?	
A)	Their gravitational fields can bend the light from background stars.	
B)	They emit copious amounts of infrared radiation, which can penetrate the interstellar medium.	
C)	Molecules in their atmospheres emit radio waves that can be detected from the Earth.	
D)	They occasionally eclipse (block the light from) more distant stars.	

25.	What has microlensing told us about the role of brown dwarfs in the Galaxy?	
A)	They cannot be a major component of the dark matter in the Galaxy.	
B)	They are a major component of the matter that is falling into the supermassive black hole in the galactic center.	
C)	They are one of the most important components of the Galaxy's dark matter.	
D)	It has told us almost nothing yet—microlensing is too difficult to observe.	

Answer Key

1.	A	
2.	D	
3.	A	
4.	A	
5.	A	
6.	A	
7.	B	
8.	D	
9.	A	
10.	D	
11.	A	
12.	A	
13.	D	
14.	B	
15.	C	
16.	D	
17.	B	
18.	D	
19.	B	
20.	B	
21.	D	
22.	C	
23.	C	
24.	A	
25.	A