Choose only one answer for each question
1. What is the central temperature of the sun?
a. 3000 Kelvin
b. 6000 Kelvin
c. 15 million Kelvin
d. 1 billion Kelvin
2. Where in the sun does nuclear fusion take place?
a. in the core
b. in a shell surrounding the core
c. in the convective zone
d. in the atmosphere
3. Why do we study solar oscillations (helioseismology)?
a. It allows us to predict when solar flares will erupt
b. It allows us to probe the temperature, density, and composition of
the sun below the photosphere
c. It allows us to map the surface magnetic field of the sun
d. It allows us to measure the number of neutrinos being emitted by the sun
4. Why do neutrinos let us see into the core of the sun?
a. they are easy to detect
b. they don't interact with the material outside the sun's core
c. they interact only with material on earth, not with solar material
d. they bounce around inside the sun, getting more information with each
pass through the core
5. What prevents gravity from making a Main Sequence star collapse into an
infinitely dense point?
a. centrifugal force balances the force of gravity
b. the strong nuclear force balances the force of gravity
c. gas pressure balances the force of gravity
d. electron degeneracy, or the fact that more than one electron cannot be
in the same quantum state, prevents the star from collapsing
6. A 10 solar-mass star is 40,000 times as luminous as the sun. If the
sun has a lifetime of 10 billion years, what is the lifetime of the 10
solar-mass star?
a. 2.5 million years
b. 1 billion years
c. 10 billion years
d. 100 billion years
7. Why is there a lower mass limit for Main Sequence stars?
a. stars below a certain mass don't have enough starting mass to cause
the collapse of their parent cloud
b. stars below a certain mass have strong winds, and blow themselves apart
c. stars below a certain mass don't have cores hot enough to fuse hydrogen
d. stars below a certain mass become degenerate and explode
8. What is a brown dwarf?
a. a planet the size of Jupiter
b. a white dwarf that has stopped shining
c. an object that formed like a star, but is too small to fuse hydrogen
d. a Main Sequence star much smaller than the sun
9. The sites of current massive-star formation are marked by _______________.
a. large clusters of red giants
b. ultraviolet radiation
c. neutrino emission
d. bursts of gamma rays
10. Why is dust so important in star formation?
a. it shields gas clouds from outside radiation, allowing them to cool to
the point where they can collapse to form protostars
b. dust particles collide and stick together, and eventually these
collections of dust become massive enough to fuse hydrogen
c. the heat generated by the collision of dust particles in a star
provides the initial energy needed to start hydrogen fusion
d. the dust's self-gravity holds clouds together until they can form
stars
11. Where in the galaxy are stars being formed?
a. only in the galactic center
b. in the spiral arms
c. everywhere in the galactic disk except in the spiral arms
d. in the galactic halo
12. Where do planets form?
a. in disks around low-mass stars
b. in planetary nebulae
c. in the molecular outflow from low-mass stars
d. in ionized regions around high-mass stars
13. Between the time when a star uses up its hydrogen fuel and the
time when it starts burning helium, the star _______________, and its
luminosity ________________.
a. contracts; decreases
b. contracts; increases
c. expands; decreases
d. expands; increases
14. Two star clusters, Cluster A and Cluster B, are observed. Cluster A
has many bright blue stars and many very dim red stars. Cluster B has no
bright blue stars, but has many bright red stars along with many very dim
red stars. What can we infer?
a. Cluster A is much younger than Cluster B
b. Cluster A is much older than Cluster B
c. Cluster A is much more massive than Cluster B
d. Cluster A is much less massive than Cluster B
15. What is an isochrone?
a. the age of a cluster, determined from the cluster's H-R diagram
b. the path a star follows as it evolves off the Main Sequence
c. a line in the H-R diagram connecting stars that have the same mass
and different ages
d. a line in the H-R diagram connecting stars that have the same age
and different masses
16. What is an evolutionary track?
a. the part of the H-R diagram where helium-burning stars are found
b. the point where a cluster's most massive stars still on the Main Sequence
are found
c. the path a star follows through the H-R diagram as it ages
d. a line in the H-R diagram connecting the stars in a cluster
17. Which of the following is the correct evolutionary sequence for a
one-solar-mass star?
a. protostar, horizontal branch star, asymptotic giant, Main Sequence star,
red giant, white dwarf
b. protostar, Main Sequence star, red giant, horizontal branch star,
asymptotic giant, white dwarf
c. protostar, asymptotic giant, Main Sequence star, horizontal branch star,
red giant, white dwarf
d. protostar, Main Sequence star, asymptotic giant, horizontal branch star,
red giant, white dwarf
18. A/an ________________ is a star that is undergoing steady helium fusion
in its core.
a. red giant
b. horizontal branch star
c. Main Sequence star
d. asymptotic giant
19. What is a planetary nebula?
a. the disk around a young star
b. the shell of a dying star that has become separated from its core
c. a very large giant star that has swallowed its planets
d. any glowing cloud of gas found near the ecliptic
20. Why are white dwarfs hot?
a. They are fusing carbon into magnesium in their cores
b. They were the cores of stars that were fusing helium into carbon, and
still have leftover heat from that fusion
c. They are gaining mass, and contracting due to degeneracy effects
d. They are heated by strong surface magnetic fields
B1. Why doesn't the sun explode like a hydrogen bomb?
a. any excess energy produced is turned into gravitational potential energy
b. the sun produces much less energy per second than a hydrogen bomb
c. neutrinos carry any excess energy out of the sun's interior, acting as
a safety valve
d. any excess energy produced is immediately radiated away as gamma photons
B2. Why does the degenerate core of a red giant explode like a fusion bomb?
a. the core isn't fusing, so the red giant's envelope collapses in on it,
causing a huge explosion
b. explosive helium fusion is easier to create than explosive hydrogen fusion
c. it gains mass from the red giant until it is too massive for electron
degeneracy to prevent it from exploding
d. electron degeneracy pressure is independent of temperature, so when the
temperature rises there is no thermal safety valve to prevent explosion