Astronomy 100
Section 2, Fall 2008
Homework J
Due Wednesday, December 3
On your scantron fill out your NAME, STUDENT
NUMBER, and NETWORK ID both in writing and in the
bubbles. In addition, fill out "FORM J."
1. Interstellar dust is made mostly of
a) iron and titanium
b) hydrogen and helium
c) ammonia and methane
d) silicon and carbon
e) water and carbon dioxide
2. What chills the dark clouds so that stars can form?
a) convection
b) conduction
c) radiation
d) dust that blocks starlight
e) all of the above
3. Stars are currently being born in
a) old star clusters
b) giant molecular clouds
c) the Oort comet cloud
d) diffuse nebulae
e) reflection nebulae (those that shine by reflection of light
from dust grains)
4. When the Sun was born, it was
a) brighter than now
b) somewhat dimmer than now
c) exactly the same as now
d) a white dwarf
e) much more massive than it is now
5. What observations provide the most evidence for the existence of
planets orbiting other stars?
a) direct observation of the planets
b) radio signals from intelligent life
c) observations of dusty disks around new stars
d) slight variations in the stars' radial velocities
e) none of the above; there is no evidence
6. Which kind of main sequence star will live the shortest period
of time and explode?
a) F b) O c) A d) G e) M
7. The nuclear-fusing core of the Sun is
a) slowly expanding and heating
b) slowly contracting and heating
c) staying the same
d) slowly expanding and cooling
e) slowly contracting and cooling
8. The Sun will create a
a) planetary nebula
b) white dwarf
c) giant star
d) all of the above
e) none of the above
9. What evidence is there for intelligent life in the Universe
(other than ourselves)?
a) UFOs
b) aliens on television
c) radio radiation from other stars
d) laser radiation from other stars
e) none
10. Where on the HR diagram do we find brown dwarfs?
a) at the top of the main sequence
b) below the lower end of the hydrogen-fusing main
sequence
c) on the giant branch
d) among the hot white dwarfs
e) among the cool white dwarfs
11. Above what mass (in solar masses) are main sequence stars
expected to explode, that is, to become supernovae?
a) 0.08 b) 0.8 c) 10 d) 1000 e) 1000
12. A star climbing the giant branch for the first time has a core
made of
a) helium
b) hydrogen
c) carbon
d) oxygen
e) iron
13. What keeps the Sun from contracting?
a) gravity
b) thermonuclear fusion in the core
c) rapid rotation
d) magnetic fields
e) nothing
14. The fusion of what element stops the first ascent of the giant
branch?
a) helium
b) hydrogen
c) carbon
d) oxygen
e) iron
15. What kind of radiation from hot stars lights up diffuse and
planetary nebulae?
a) red light
b) infrared light
c) radio radiation
d) ultraviolet light
e) blue light
16. What does helium fuse into?
a) silicon
b) hydrogen
c) iron
d) carbon
e) nothing
17. What kinds of stars fuse helium?
a) white dwarfs
b) stars like the Sun
c) stars just being born
d) giant stars
e) none
18. White dwarfs are made mostly of
a) hydrogen
b) helium and hydrogen
c) carbon and oxygen
d) iron and nickel
e) titanium and vanadium
19. Stars like Mira, those climbing the giant branch for the second
time, will turn into
a) supernovae
b) planetary nebulae
c) brown dwarfs
d) main sequence stars
e) diffuse nebulae
20. What stage of stellar life follows the planetary nebula?
a) red giant
b) nothing
c) supernova
d) white dwarf
e) brown dwarf
21. White dwarfs are formed by stars that start off in the mass
range
a) 0.8 to 10 solar
b) 10 to 100 solar
c) 0.08 to 0.8 solar
d) under 0.08 solar
e) over 100 solar
22. The maximum allowed mass for a white dwarf is (in solar
masses)
a) 0.08 b) 0.8 c) 1.0 d) 1.4 e) 2.8
23. White dwarfs do not collapse under their own gravity because
of
a) hydrogen fusion
b) helium fusion
c) carbon fusion
d) the pressure of degenerate protons
e) the pressure of degenerate electrons
24. What do old planetary nebulae have at their centers?
a) new white dwarfs
b) neutron stars
c) giant stars
d) supergiant stars
e) main sequence stars
25. What do second-ascent giant stars have in their cores?
a) helium
b) hydrogen
c) carbon and oxygen
d) silicon
e) iron