Name: __________________________  Date: _____________

1.	Interstellar extinction is	
A)	the assimilation of interstellar matter by stars after gravitational attraction and capture.	
B)	the reduction of the apparent brightness of stars by scattering and absorption of their light by intervening interstellar clouds.	
C)	the wipe-out of species on the Earth by intense radiation from a nearby supernova.	
D)	the deaths of high-mass stars in the space between other long-lived stars.	

2.	What are the two most abundant elements in the universe?	
A)	Hydrogen and carbon	
B)	Hydrogen and oxygen	
C)	Hydrogen and helium	
D)	Nitrogen and oxygen	

3.	How is gas distributed in interstellar space?	
A)	In clumps, concentrated in interstellar clouds	
B)	Concentrated in narrow riverlike streams of gas that extend across the Galaxy	
C)	Uniformly distributed through space	
D)	Concentrated around existing stars because of the stars' gravitational pull	

4.	What is the characteristic color of a reflection nebula?	
A)	Red	
B)	Yellow	
C)	Green	
D)	Blue	

5.	A reflection nebula is made visible by	
A)	thermal energy emitted as a continuous spectrum by the very hot gas, much like that emitted by a hot body on the Earth.	
B)	light from embedded stars reflected over a wide range of wavelengths toward the Earth by crystals of water, methane, and ammonia ices.	
C)	emission lines from hydrogen, which itself has been ionized by UV light from embedded stars.	
D)	blue light preferentially scattered by dust grains.	

6.	Which of the following is true about open clusters?	
A)	They will all slowly condense into globular clusters, the stars having driven off the remaining interstellar dust and gas.	
B)	One star in an open cluster will eventually undergo a supernova explosion that will quickly disperse the other stars.	
C)	As they slowly condense, their residual rotation will spin them into a flat pancake shape and they will become spiral galaxies.	
D)	The motions of individual stars are such that all open clusters will eventually disperse.	

7.	New stars are formed from	
A)	hot supernova remnants.	
B)	activity around black holes in the centers of galaxies.	
C)	huge, cool dust and gas clouds.	
D)	pure energy in free space.	

8.	What is the typical temperature inside the dense core of a giant molecular cloud that is collapsing to form a star?	
A)	Less than 1 K	
B)	10 K	
C)	1000 K	
D)	100 K	

9.	The characteristics of an open cluster of stars are	
A)	a few hundred members, often very young and still embedded in the gas and dust from which they were formed.	
B)	hundreds of thousands of members, all very old, surrounded by very little interstellar gas and dust.	
C)	a few dozen members, the remnant of a globular cluster of stars from which most of the members have escaped.	
D)	many thousands of members of different ages.	

10.	Protostars are	
A)	very young objects still contracting before becoming true stars.	
B)	old stars contracting after using up all of their available hydrogen fuel.	
C)	objects with masses less than about 0.08 solar masses that do not have enough mass to become true stars.	
D)	stars made almost entirely out of protons.	

11.	What is the most important process causing a protostar to stop accreting mass?	
A)	Radiation and particles from the hot protostar push infalling matter away from the protostar.	
B)	Other protostars formed in the vicinity pass randomly through the infalling material and eventually disperse it.	
C)	The dense core spins up as it collapses, and eventually the infalling matter is held away from the protostar by the centrifugal force.	
D)	All of the infalling matter has been used up in the accretion.	

12.	What event occurs at the end of the protostar stage of a star's life?	
A)	It explodes, forming a supernova remnant.	
B)	Gas is spun off from its equator, from which planets may form.	
C)	Nuclear reactions begin in its core, converting hydrogen into helium.	
D)	It begins a long period of contraction in which gravitational energy is converted into heat.	

13.	The “evolutionary track” of a star represents	
A)	its orbit around the center of the galaxy in which it resides.	
B)	changes in its luminosity and temperature on a graph of these two parameters as the star ages.	
C)	its path across our sky as a consequence of its true motion in space.	
D)	changes in its size and mass on a graph of these two parameters as the star ages.	

14.	A brown dwarf is	
A)	an object intermediate between a planet and a star, with not enough mass to begin nuclear reactions in its core.	
B)	a general name for objects similar to the planet Jupiter.	
C)	any star whose blackbody spectrum peaks in the brown region of the visible spectrum.	
D)	a star of less than about 1.5 solar masses at the very end of its life, after it has cooled to near invisibility.	

15.	What is believed to prevent stars from having masses greater than a few hundred solar masses?	
A)	Stars of larger mass would collapse under their own gravity and become black holes.	
B)	No interstellar clouds have masses of more than 100 solar masses.	
C)	The cores of larger-mass stars would run through their lives and explode before the stars finish contracting as protostars.	
D)	The temperature becomes so high that the excess mass is pushed back into space by radiation from the star.	

16.	If we plotted the stars in a YOUNG star cluster on a Hertzsprung-Russell diagram, we would expect to see	
A)	all stars on the main sequence.	
B)	the more massive stars above the main sequence and the less massive stars on the main sequence.	
C)	some stars on the main sequence and others above the main sequence, in random fashion depending on when each individual star condensed from the interstellar cloud.	
D)	the more massive stars on the main sequence and the less massive stars above the main sequence.	

17.	The definition of a main-sequence star is one	
A)	with a surface temperature equal to that of the Sun.	
B)	in which nuclear fusion reactions generate sufficient energy to oppose further condensation of the star.	
C)	whose age after birth is about 1 million years.	
D)	with a luminosity precisely equal to that of the Sun.	

18.	The “zero-age main sequence” describes the sequence of stars in the Hertzsprung-Russell diagram	
A)	that contain no processed elements (elements heavier than hydrogen or helium).	
B)	that are just beginning to convert helium into carbon in their cores.	
C)	that have just collapsed from the interstellar medium.	
D)	that have just reached the main sequence.	

19.	The total time that the Sun will spend as a main-sequence star is	
A)	at least 200 billion years (2 × 1011) years.	
B)	about 1 million years.	
C)	about 4.5 million years.	
D)	about 10 billion years (1010 years).	

20.	The stars that last longest are	
A)	those with the largest luminosity and highest temerature since they will take the longest to cool down to invisibility.	
B)	those with the largest mass, that is, the largest amount of fuel.	
C)	those with the smallest mass.	
D)	stars of intermediate mass; small-mass stars have little fuel and burn out quickly, while very massive stars burn their fuel very rapidly.	

21.	Why does the core of the Sun contain more helium and less hydrogen than the surface of the Sun?	
A)	The hydrogen has been lifted out of the core by the Sun's magnetic field.	
B)	Helium is heavier than hydrogen and has sunk toward the center in a process of chemical differentiation.	
C)	Helium condenses more easily, so when the Sun was forming the core became helium-rich; vast quantities of hydrogen were added only after the core became massive enough.	
D)	Thermonuclear reactions have converted much of the original hydrogen in the core into helium.	

22.	The next stage in a star's life after the main-sequence phase is	
A)	the red-giant phase.	
B)	the horizontal-branch phase.	
C)	a protostar.	
D)	death (i.e., either a supernova or a white dwarf).	

23.	What makes a red giant star so large?	
A)	The helium-rich core has expanded, pushing the outer layers of the star outward.	
B)	The hydrogen-burning shell is heating the envelope and making it expand.	
C)	Red giants are rapid rotators, and centrifugal force pushes the surface of the star outward.	
D)	The star has many times more mass than the Sun.	

24.	How large will the Sun be as a red giant?	
A)	About 1 AU radius (out to the Earth's orbit)	
B)	About 1/10 AU radius (1/4 of Mercury's orbit)	
C)	About 1.5 AU radius (out to Mars's orbit)	
D)	About 1/2 AU radius (beyond Mercury's orbit)	

25.	What happens to the helium-rich core of a star after the core runs out of hydrogen?	
A)	It cools down and contracts.	
B)	It expands and cools down.	
C)	It heats up and expands.	
D)	It contracts and heats up.	

26.	When is electron degeneracy pressure important in a star?	
A)	Just before the start of helium burning in the core	
B)	During core hydrogen burning	
C)	In a Cepheid variable that is burning helium in its core	
D)	In a protostar evolving toward the main sequence	

27.	The study of stars in clusters has especially helped astronomers to understand	
A)	stellar evolution, the development of stars with time.	
B)	the mechanism of mass loss in stars.	
C)	the reason for differences in surface temperatures of stars.	
D)	the action of nuclear fusion in stars.	

28.	The characteristic of a globular cluster of stars is	
A)	hundreds of thousands of members, all very old and generally metal-poor.	
B)	a few dozen members, the remnant of a globular cluster of stars from which most of the members have escaped.	
C)	many thousands of members of different ages.	
D)	a few hundred members, often very young and still embedded in the gas and dust from which they were formed.	

29.	Which of the following stars are metal-rich?	
A)	Population I stars	
B)	Very old stars	
C)	Population II stars	
D)	Globular cluster stars	

30.	What is the “turnoff” point for a star cluster?	
A)	The point in the Hertzsprung-Russell diagram occupied by stars undergoing (or about to undergo) the helium flash	
B)	The point in the Hertzsprung-Russell diagram occupied by the highest-mass main-sequence stars in the cluster	
C)	The point in the Hertzsprung-Russell diagram occupied by the lowest-mass main-sequence stars in the cluster	
D)	The point in the Hertzsprung-Russell diagram occupied by the highest-mass stars that have not yet reached the main sequence	

31.	What is a Cepheid variable star?	
A)	One of several classes of stars that pulsate randomly in brightness	
B)	A low-mass, horizontal-branch star that pulsates regularly in brightness	
C)	A star that normally remains constant in brightness but occasionally flares up in brightness by several magnitudes	
D)	A high-mass star that pulsates regularly in brightness	

32.	What characteristic of Cepheid variables makes them extremely useful to astronomers?	
A)	Their absolute magnitude is related directly to their period of pulsation.	
B)	Their absolute magnitude is directly related to their diameter.	
C)	Their absolute magnitude is related directly to their metal content (heavy element abundance).	
D)	Their absolute magnitude is related directly to their surface temperature.	

Answer Key

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