S.D.
Marcum
Astronomy
& Space Physics
EXAM
3 - ***FORM 1***
Name
__________________________
INSTRUCTIONS: Fill
in your Student ID# and the FORM NUMBER of your
exam
on the answer sheet. Choose
the BEST answer for each question and
mark
your choice on the answer sheet. Use
a #2 pencil only. The ESSAY
question
is on the last page, tear it free and turn it in separately.
Re-insert
the answer sheet into the test packet and turn both in.
1.
Which of the following statements is NOT true for sunspots?
a.
They are cooler than the surrounding photosphere of the Sun.
b.
They often occur in pairs of opposite magnetic polarity.
*c.
They occur in regions of lower-than-average magnetic fields.
d.
They increase and decrease in number, relatively regularly.
2.
The relationship between mass and luminosity of stars on the main
sequence
is that
a.
luminosity is independent of the stellar mass.
b.
the greater the stellar mass, the less the luminosity.
*c.
the larger the stellar mass, the larger the luminosity.
d.
the luminosity of stars reaches a peak at around 1 solar mass,
and
decreases as mass increases and decreases beyond this limit.
3.
One important aspect of the study of binary star systems, as
distinct
from single stars, is that it provides
a.
a measurement of the composition (abundances of elements) inside
stars.
*b.
a measurement of the masses of stars.
c.
a verification of the Doppler equation for wavelength shift of
light
from moving objects.
d.
a measurement of the surface temperatures of stars.
4.
The 11 year sunspot cycle on the Sun is
a.
an extremely regular build-up and decay of the number of
sunspots,
with a precise period of 11.3 years.
*b.
an irregular cycle averaging about 11 years, but sometimes
disappearing
entirely.
c.
a somewhat irregular but always present cycle of build-up and
decay
of sunspot numbers.
d.
the regular movement of a relatively constant number of sunspots
from
the poles to the equator of the Sun over an 11-year period.
5.
How do massive stars normally end their lives?
*a.
They explode.
b.
They gradually shrink to the size of the Earth.
c.
We don't know, since their lifetimes are longer than the age of
the
universe.
d.
They collapse and become black holes.
6.
The diameter of a typical neutron star of 1 solar mass is predicted
to
be approximately
a.
that of the Sun.
*b.
that of an average city, a few km.
c.
that of Earth, 12,800 km.
d.
1 km.
7.
The spectral class of the star Enif is K2 while that of the Sun is
G2.
Which of the following conclusions can be drawn about Enif from
this
information?
a.
It is intrinsically brighter than the Sun.
b.
It is hotter than the Sun.
*c.
It is cooler than the Sun.
d.
It is intrinsically fainter than the Sun.
8.
A high-mass star near the end of its life undergoes successive
cycles
of energy generation within its core in which gravitational
collapse
increases the temperature to the point where a new nuclear
fusion
cycle generates sufficient energy to stop the collapse. This
process
does not work beyond the silicon fusion cycle that produces
iron.
Why is this?
*a.
Fusion of iron nuclei into heavier nuclei requires energy rather
than
producing excess energy and therefore will not produce the
additional
gas pressure to halt the collapse.
b.
Iron nuclei are so large that they occupy all remaining space and
so
the collapse cannot continue.
c.
Electrostatic forces between the highly charged iron nuclei are
sufficient
to overcome the collapse and stabilize the stellar
core.
d.
The pressure from high-energy photons and neutrinos at the very
high
core temperatures reached at this stage of development is
finally
sufficient to halt the collapse.
9.
The Hertzsprung-Russell diagram is a plot of
a.
apparent brightness against distance for stars near to the Sun.
b.
apparent brightness against intrinsic brightness of a group of
stars.
c.
luminosity against mass of a group of stars.
*d.
absolute magnitude (or intrinsic brightness) against temperature
of
a group of stars
10.
The temperature of the Sun's photosphere is
*a.
5,800 K.
b.
close to 1 million K.
c.
4,300 K.
d.
about 10,000 K.
11.
A hydrogen nucleus (a proton) has a charge of +1 and a helium
nucleus
has a charge of +2. Why, then, does it require four protons
to
form helium in the core of the Sun?
*a.
Two of the protons become neutrons.
b.
Two helium nuclei are formed from the four protons.
c.
Two of the protons are ejected back into the solar material.
d.
Two of the protons are converted into neutrinos.
12.
How long will the Sun have spent as a main sequence star when it
finally
begins to evolve toward the red giant phase?
a.
1 billion years
b.
1 million years
c.
1011 years
*d.
1010 years
13.
Which of the following sequences of stellar spectral classifications
is
in correct order of increasing temperature?
a.
O,B,A,F,G,K,M
*b.
M,K,G,F,A,B,O
c.
A,B,F,G,K,M,O
d.
K,M,G,F,A,B,O
14.
The neutrino is
a.
another name for an electron that carries a positive charge
instead
of a negative charge.
b.
a heavy, uncharged nuclear particle, easily detected.
*c.
an elusive, subatomic particle having little or no mass, and
difficult
to detect.
d.
a very small asteroidlike body orbiting the Sun.
15.
How is the length of a star's lifetime related to the mass of the
star?
*a.
Higher-mass stars run through their lives faster and have shorter
lifetimes.
b.
Lower-mass stars run through their lives faster and have shorter
lifetimes.
c.
A star's lifetime does not depend on its mass.
d.
The lifetimes of stars are too long to measure, so it is not
known
how (or if) their lifetimes depend on mass.
16.
What happens to the helium-rich core of a star after the core runs
out
of hydrogen?
*a.
It contracts and heats up.
b.
It cools down and contracts.
c.
It expands and cools down.
d.
It heats up and expands.
17.
If the surface temperature of white dwarf stars is four times that
of
the Sun and energy output per unit area of a star depends on the
4th
power of the temperature by the Stefan-Boltzmann relation, why
then
are white dwarfs intrinsically so faint?
a.
Because they are moving rapidly away from the Sun and their
spectra
are extremely red-shifted, hence they appear faint at
visible
wavelengths.
*b.
Because they are very small.
c.
Because they are shrouded in very thick atmospheres.
d.
Because they have very thin atmospheres that do not emit
continuum
radiation but only line emissions, like a low density
gas.
18.
Thermonuclear fusion reactions in the core of the Sun convert four
hydrogen
atoms into one helium atom. The helium atom has
a.
more mass than the four hydrogen atoms, because energy is
produced
in the reaction, and the energy adds mass by E = mc2.
*b.
less mass than the four hydrogen atoms, because the energy
produced
is lost from the atom, and energy is equivalent to mass
by
E = mc2.
c.
the same mass as the four hydrogen atoms, because any product has
to
equal the sum of its parts.
d.
an undetermined amount of mass, depending on the temperature at
which
the reaction occurs.
19.
A protostar of about 1 solar mass is gradually contracting and
becoming
hotter. This will cause its position in the
Hertzsprung-Russell
diagram to shift slowly
a.
upward and toward the left.
b.
downward and toward the right.
*c.
downward and toward the left.
d.
upward and toward the right.
20.
Which part of the Hertzsprung-Russell diagram is occupied by
protostars?
*a.
to the right of the main sequence
b.
to the left of the main sequence
c.
a band running from upper left to lower right
d.
a band running from upper right to lower left
21.
Which of the following major perturbations can occur to a close
binary
system and radically alter the evolution and behavior of the
two
individual stars?
a.
The heating of the localized areas of the atmosphere of one star
by
its companion.
*b.
The transfer of matter from one star to its companion.
c.
The eclipsing of the light from one star by the other, when
viewed
from Earth.
d.
The gravitational disturbance of one star's motion by its
companion,
to force it to move in an orbit.
22.
What is a pulsar?
*a.
A rapidly rotating neutron star, producing beams of radio energy
and
occasionally x rays and visible light.
b.
A pulsating white dwarf star, fluctuating rapidly in brightness.
c.
A Cepheid variable star with a period of a few days.
d.
Very hot material orbiting a black hole.
23.
Granulation or the mottled appearance of the whole solar surface is
an
indication of what physical process at work in the Sun?
a.
rapid rotation of the Sun
b.
the outflow of neutrinos from the interior
c.
thermonuclear fusion of hydrogen in the Sun's surface layers
*d.
convective motion of gases in the upper portion of the Sun's
interior.
24.
Where are the most massive stars to be found in the main sequence of
a
Hertzsprung-Russell diagram?
a.
The lower, right end.
b.
In the center section near to the Sun's position, with lower mass
stars
on either side.
*c.
The upper, left end.
d.
Main sequence stars all have approximately the same mass, by
definition.
25.
The most likely places where stars and planetary systems are forming
in
the universe are
a.
in the centers of galaxies.
*b.
in nebulae composed of gas and dust.
c.
in the rarified space between galaxies.
d.
in regions surrounding quasars.
26.
Which of the following observations would NOT be an indication of a
binary
star system?
a.
A "star" appears to become periodically dimmer for a few hours at
a
time.
b.
A "star" image separates into two distinct images periodically
and
then blends again, periodically.
c.
The "star" appears to wiggle in its path across our sky against
the
background stars.
*d.
The "star" appears to move in a straight line against a
background
field of stars.
27.
A planetary nebula is
a.
a disk-shaped nebula of dust and gas rotating around a relatively
young
star, within which planets will eventually form.
b.
the nebula caused by the supernova explosion of a massive star.
c.
a contracting spherical cloud of gas surrounding a newly formed
star
in which planets are forming.
*d.
a gas shell, the atmosphere of a red giant star, slowly expanding
away
from a hot white dwarf, the core of the red giant.
28.
Which is the correct sequence for the following end-points of
stellar
evolution, in order of increasing mass?
a.
white dwarf, black hole, neutron star
b.
black hole, neutron star, white dwarf
*c.
white dwarf, neutron star, black hole
d.
neutron star, black hole, white dwarf
29.
Which of the following types of stars or stellar remnants can have a
mass
no larger than about 1.4 times the mass of the Sun, otherwise
they
will collapse under their own gravity?
a.
red giants
b.
neutron stars
*c.
white dwarfs
d.
black holes
30.
What stops the Sun from collapsing under the force of its own
gravity?
*a.
It is held up by gas pressure due to the very high temperature
inside
it.
b.
Neutrinos from the core collide with gas atoms and prevent them
from
falling inwards.
c.
Ions and electrons are pushed apart by the electric forces
between
their charges.
d.
The interior of the Sun is under such high pressure that it is a
liquid,
and liquids are incompressible.
31.
An astronomer plots the HR diagram of a star cluster and finds that
it
contains hot B-type stars on the main sequence and cooler G- and
K-type
stars noticeably above the main sequence. This cluster is
*a.
very young, because the G and K stars are still evolving towards
the
main sequence.
b.
old, because the G and K stars are already evolving off (away
from)
the main sequence.
c.
of indeterminate age, since one cannot estimate the age of the
cluster
from the information given.
d.
impossible, because one cannot have cool stars above the main
sequence
when hot stars are on the main sequence.
32.
Our Sun will end its life by becoming
*a.
a white dwarf.
b.
a pulsar.
c.
a black hole.
d.
a molecular cloud.
33.
What problem have observers of solar neutrinos run into?
*a.
Only about 1/3 of the expected number of neutrinos is observed,
compared
to theoretical models of the Sun.
b.
About six times as many neutrinos are observed than expected from
theoretical
models of the Sun
c.
The neutrinos are about twice as energetic on average than is
predicted
by theoretical models of the Sun.
d.
The neutrinos are of the wrong type (muon neutrinos, instead of
the
predicted electron neutrinos).
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