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Chapter 27 Stars and Galaxies
27.1 Observing the Night Sky
1) What is the upper limit of stars the unaided eye can discern on a moonless night in a rural
A) About 3,000
B) About 30,000
C) About 300,000
D) About 3,000,000
Answer: A
2) The diurnal rotation of the stars refers to the
A) apparent rotation of the celestial sphere due to the rotation of the Earth.
B) movement of the stars across the sky during daytime hours.
C) rate of spin of stars in their formation stage.
D) particular constellations that are visible in different times of the year.
Answer: A
3) The North Star has very little apparent rotation in the night sky because
A) it lies directly above the Earth's axis of spin.
B) it rotates in the same relative orbit as Earth.
C) its rate of spin directly matches Earth's.
D) the Oort cloud distorts the view of the naked eye.
Answer: A
4) Which best describes the intrinsic motion of stars?

A) Their circular motion across the sky in a 24-hour period
B) Their apparent yearly cycle around the Sun, due to Earth's revolution
C) Their motion relative to all other bodies
D) Their motion relative to Earth
Answer: C
5) How far is a light year?
A) Nearly 10 trillion km
B) The distance of one Earth orbit.
C) 300,000 km
D) All of the above
Answer: A
6) We say we are looking back in time when we are looking at the stars because
A) we see stars as they once were when their light reaches us.
B) space curves, we are actually looking at the past when we look in the night sky.
C) stars are emitting immense radiation, we are seeing processes that have already happened.
D) Earth's atmosphere bends and distorts their light.
Answer: A
7) Summer and winter constellations are different because
A) of the spin of the Earth about its polar axis.
B) the night sky faces in opposite directions in summer and winter.
C) of the tilt of the Earth's polar axis.
D) the Earth is at the solar perigee in winter and apogee in summer.

E) the universe is symmetric.
Answer: B
8) Polaris is always directly overhead at
A) the north pole.
B) any location north of the equator.
C) the equator.
Answer: A
9) In which city is Polaris highest in the sky?
A) Singapore
B) Mexico City
C) Denver
D) Anchorage
E) All the same, depending on the time of night
Answer: D
10) The background stars during a solar eclipse are those of constellations
A) of the opposite season.
B) seen in the nighttime sky.
C) not seen normally.
D) seen in the opposite hemisphere.
Answer: A
11) The star nearest the Earth is
A) the Sun.

B) Alpha Centauri.
C) Polaris.
D) the Moon.
Answer: A
12) We do not see stars in the daytime because
A) the Sun blocks their view.
B) they simply don't exist in the daytime part of the sky.
C) skylight overwhelms starlight.
D) of the lack of contrast with moonlight.
E) the solar wind obscures their view.
Answer: C
27.2 The Brightness and Color of Stars
1) What are the relative compositions of the materials from which stars form?
A) About 74% hydrogen, about 24% helium, no more than 2% other materials
B) About 24% hydrogen, about 74% helium, no more than 2% other materials
C) About 2% hydrogen, about 74% helium, no more than 24% other materials
D) Stars have vastly differing combinations of materials.
Answer: A
2) A star's luminosity tells us
A) how much energy a star produces.
B) its surface temperature.
C) its rotational speed.

D) both how much energy it produces and its surface temperature.
Answer: A
3) A star's color tells us
A) how much energy a star produces.
B) its surface temperature.
C) its rotational speed.
D) both how much energy it produces and its surface temperature.
Answer: B
4) The stars Procyon and Betelgeuse both appear equally bright to Earthbound viewers. Yet
Betelgeuse emits 5000 times more light than Procyon. Why do they appear to be equally bright?
A) Because Betelgeuse is much farther than Procyon
B) Because Betelgeuse is undergoing fission, not fusion
C) Because Betelgeuse lies in the same plane of Earth's orbit
D) Because Procyon is superhot
Answer: A
5) Luminosity is
A) the total amount of light energy that star emits into space.
B) the stars apparent brightness.
C) the stars particular color spectrum output.
D) the stars total infrared output.
Answer: A
6) What is the reference that astronomers use to denote the luminosity of stars?

A) The luminosity of the Sun
B) The luminosity of the Northern Star
C) The luminosity of Proxima Centauri, our solar system's closest neighbor star
D) The luminosity of the cluster of stars at the center of the Milky Way galaxy
Answer: A
7) Why does a star's color corresponds to its temperature?
A) Higher temperature means more energetic light, which is seen as higher frequencies.
B) Because of the light shifts that take place when star light interacts with the Earth's atmosphere
C) Because the core temperature averages with the surface temperature to create an overall color
D) Because the ultraviolet output of a star directly modifies the visible light spectrum the star is
Answer: A
8) Which star will emit the shortest wavelength of its peak frequency?
A) A blue star
B) A yellow star
C) A red star
D) A green star
Answer: A
9) Thermonuclear fusion occurs mainly in the
A) cores of stars.
B) outer layers of stars.
C) both, actually

Answer: A
10) The temperature of a star is evidenced by its
A) brightness.
B) color.
C) angular momentum.
D) distance.
E) rate of burning.
Answer: B
27.3 The Hertzsprung-Russell Diagram
1) On the H-R diagram our Sun is a
A) white dwarf.
B) star of average luminosity and temperature.
C) red supergiant.
D) relatively bright, blue star.
Answer: B
2) Red giant stars are
A) close to exhausting their supply of hydrogen.
B) have already exhausted their supply of hydrogen.
C) are close to exhausting their supply of helium.
D) have already exhausted their supply of helium.
Answer: A

3) Which is greater, the gravitational attraction between a newborn baby and the Earth, or the
gravitational attraction between the Earth and all the planets of the solar system?
A) The attraction between the baby and Earth
B) The attraction between the planets and Earth
C) They are roughly equal
D) The baby's and the planets gravitational attractions are inversely proportional to each other
Answer: A
4) The event that changes a protostar to a full-fledged star is
A) gravitational collapse.
B) gravitational expansion.
C) thermonuclear fusion.
D) the emission of light.
E) a catastrophic increase in temperature.
Answer: C
5) The longest living stars are those of
A) low mass.
B) high mass.
C) intermediate mass.
Answer: A
6) The masses of stars are found by measurements of
A) light intensity.
B) temperature.

C) Doppler shifting.
D) binaries.
E) relative sizes.
Answer: D
7) The H-R Diagram, an important tool of astronomers, relates stellar temperature to stellar
A) distance.
B) mass.
C) color.
D) density.
E) luminosity.
Answer: E
8) What are the outward forces that act on a star? What are the inward forces? How do these
Answer: The outward forces on a star are radiation pressure caused by nuclear fusion in the
stellar cores. This tends to blow up the star. The inward forces are due to gravitation, which tend
to compress the star. How do these opposite forces compare? They're equal, and determine the
size of the star. When one becomes stronger than the other, the size of the star changes.
27.4 The Life Cycles of Stars
1) A star's size stabilizes when
A) thermal pressure and gravitational attraction balance each other.
B) the star's gravitational attraction is balanced by the gravitational attraction to neighboring
C) the star first ignites.
D) it reaches temperatures of about 3 million K.

Answer: A
2) The determining factor in the stages a star will progress through from birth to death is its
A) mass.
B) temperature.
C) composition.
D) relative density.
Answer: A
3) What prevents stars greater than about 100 times the Sun's mass from existing?
A) The rate of thermal expansion would overcome gravitational attraction leading to explosion
B) The gravitational attraction would overcome the rate of thermal expansion leading to a black
C) Fusion cannot take place at these higher mass levels
D) The gaseous material of the universe is too widely dispersed to allow for the formation of
stars of this mass
Answer: A
4) How is a larger star like an SUV, while a smaller star like a fuel efficient hybrid vehicle?
A) The larger the star, the faster it burns fuel.
B) The larger the star, the more likely it is to explode.
C) The larger the star, the shorter its life span.
D) Larger stars have only one source of energy.
Answer: A
5) What event will eventually move an average star off the main sequence of the H-R diagram?

A) Running out of hydrogen, causing gravitational influx, resulting in core temperatures high
enough to begin fusing helium
B) Surface cooling due to hydrogen loss
C) Solar wind storms
D) Its drift through space due to the gravitational attraction of neighboring giant stars
Answer: A
6) What is generally the range of a star's hydrogen burning lifetime?
A) From a few million to 50 billion years
B) From a few hundred thousand to 20 billion years
C) From 20 billion to 100 billion years
D) From 2 billion to 15 billion years
Answer: A
7) What will be the predominant element within the Sun after it has died?
A) Helium
B) Nitrogen
C) Carbon
D) Phosphorous
Answer: C
8) What do astronomers expect will be left at the center of our solar system once the Sun has
gone through all its life stages?
A) A planet sized diamond
B) A red giant
C) A black hole

D) A wormhole
Answer: A
9) What will halt the collapsing Sun's core once its fuel has been exhausted?
A) The inability of electrons to enter into neighboring electrons quantum state
B) Outward thermal pressure
C) Random quantum fluctuations
D) The shift from fusion to fission nuclear reactions
Answer: A
10) Because a white dwarf is no longer burning fuel, it is more accurately described as being a
A) stellar remnant
B) failed star
C) protostar
D) black elf
Answer: A
11) Supernovae are one of the most extreme events in the known universe. They are caused by
A) the implosion of a white dwarf, which has run out of all its fuel.
B) a supermassive supergiant star undergoing a massive nuclear chain reaction.
C) the collapse of a supermassive supergiant star.
D) Any of the above.
Answer: C
12) Why can't any star, no matter how massive, fuse elements heavier than iron?
A) Because the nucleons within iron have the least mass possible

B) Because elements heavier than iron have less average mass per nucleon
C) It could happen, we just have not yet observed a star massive enough to do this.
D) Actually, this occurs on a regular basis, which explains the great abundance of heavy
Answer: A
13) Why are elements heavier than iron less abundant than those that are lighter?
A) Because the duration of a supernova is relatively short
B) Because they tend to be unstable, and easily undergo fission
C) Spectral evidence suggests they are only rare here on Earth
D) This is one of the mysteries of cosmic formation that has yet to be answered.
Answer: A
14) Most of the energy during the collapse of the iron core of a supergiant star is released in the
form of neutrinos—nearly massless subatomic particles that rarely interact with matter. So how
is it they can blow away a stars outer shells?
A) Although they rarely interact with matter, the sheer number released during the collapse is
enough to move most of the star's mass into surrounding space at incredibly high rates of speed
B) By creating a massive magnetic field that convulses in on itself, ripping away the stars outer
C) When neutrinos exceed a certain speed, 22,300 km/s, they interact with matter quite
D) By developing a temporary, but relatively strong positive charge
Answer: A
15) It is theorized that a pulsar only emits X-rays and visible light during its early history. What
do you suppose is the basis of this theory?

A) As the pulsar's energy dissipates, the frequency of the energy it emits drops.
B) X-rays are likely the result of radioactive decay, which only can occur in a pulsar's early
C) X-rays and visible light are both part of the electromagnetic spectrum.
D) The pulsars high rate of spin produces a magnetic field that, over time, slows the pulsar down.
Answer: A
16) The gold in Uncle Harry's teeth fillings originated in
A) the deep interior of the Earth.
B) fusion processes that date back about 5.5 billion years.
C) the Big Bang.
D) stars that blew up eons ago.
E) Fort Knox.
Answer: D
17) Metals are relatively more abundant in
A) old stars.
B) new stars.
C) neither in particular
Answer: B
18) After our Sun burns its supply of hydrogen, it will become a
A) white dwarf.
B) black dwarf.
C) black hole.

D) red giant.
E) blue giant.
Answer: D
19) A white dwarf is a former
A) low-mass star.
B) high-mass star.
C) white giant.
Answer: A
20) Which one of these elements is normally the remnant of a supernova?
A) hydrogen
B) helium
C) silver
D) none of these
Answer: C
21) The elements found on Earth have much to do with
A) white dwarfs.
B) neutron stars.
C) pulsars.
D) quasars.
E) supernovae.
Answer: E
22) A pulsar is likely a

A) throbbing star in its death throes.
B) black hole companion.
C) spinning neutron star.
D) binary star with a dark companion.
Answer: C
23) Most of the atoms in the universe are thought to be
A) hydrogen.
B) helium.
C) about equal amounts of hydrogen and helium.
D) iron.
E) elements unknown at present.
Answer: A
24) What event marks the birth of a star, and what event marks its death?
Answer: A stellar body becomes a star when thermonuclear fusion is ignited in its core. Death
occurs when its nuclear fires go out–when nuclear fusion ceases.
25) What happens to a star when the fusion cycle gets to the element iron?
Answer: When elements near iron, or iron itself is fused, energy is absorbed by the fusion
reaction instead of released. This cools rather than heats the star, and the show is over. The star
then undergoes collapse without rekindling. The most massive of these stars may supernova.
27.5 Black Holes
1) A black hole is
A) a region of space that is collapsed in on itself.
B) the result of the collapse of supergiant star.

C) likely found at the center of each spiral galaxy.
D) All of the above
Answer: D
2) A black hole has
A) about the same mass as the original star from which it formed.
B) infinite mass.
C) about half the mass of the star from which it formed.
D) a mass that widely fluctuates.
Answer: A
3) The event horizon of a black hole is
A) the surface below which no matter or energy can escape.
B) the surface where light becomes trapped in a circular orbit around the black hole.
C) the physical surface of the black hole.
D) the point in time when a black hole comes into being.
Answer: A
4) What determines if a star becomes a white dwarf, a neutron star, or a black hole?
A) The principal factor is mass
B) The principal factor is density
C) The principal factor is temperature
D) The principal factor is luminosity
Answer: A
5) A black hole is

A) an empty region of space with a huge gravitational field.
B) a small region that has the mass of many galaxies.
C) the remains of a giant collapsed star.
Answer: C
6) If the Sun collapsed to become a black hole, the Earth's gravitational attraction to it would be
A) more.
B) less.
C) no different.
Answer: C
7) When a star collapses to become a black hole, its mass
A) increases.
B) decreases.
C) remains unchanged.
Answer: C
8) Compared to the event horizon, the photon sphere of a black hole is
A) nearer the singularity.
B) farther from the singularity.
C) at the same location.
Answer: B
9) When a star collapses to half size, the gravitational field at its surface
A) doubles.
B) quadruples.

C) increases eightfold.
D) remains constant.
Answer: B
10) If a star collapses to a tenth its size, gravitation at its surface increases by
A) ten.
B) twenty.
C) one hundred.
D) one thousand.
E) more than one thousand.
Answer: C
11) As more and more mass falls into a black hole, the radius of its photon sphere
A) increases.
B) decreases.
C) remains unaffected.
Answer: B
12) As a star undergoes collapse, its rate of rotation
A) decreases.
B) increases.
C) remains constant.
Answer: B
13) If the Sun collapsed to a black hole, the time required for the Earth to orbit the collapsed Sun

A) increase.
B) decrease.
C) stay the same.
Answer: C
14) How does the mass of a giant star compare with the mass of the black hole it may become?
How do the densities compare?
Answer: The masses are the same! A black hole is a collapsed star, with its mass enormously
compressed, but not increased. The density of a black hole is enormously greater, but not
because of more mass, but because of less volume.
15) Describe the fate of planet Earth if the Sun were to collapse to a black hole.
Answer: First of all, the orbit of the Earth would be no different for it would be circling the same
mass either way. The mass of the Sun would be no different collapsed. But the energy the Sun
presently provides would not be there. Earth would be a very dark and cold place, and the Sun
would no longer sustain Earthly life.
27.6 Galaxies
1) One of Edwin Hubble's discoveries is that the known universe is expanding. This means that
A) most all observable galaxies are moving away from each other.
B) light rays bend as they near the event horizon of a black hole.
C) light rays undergo acceleration as they travel vast distances.
D) the mass of the universe is slowly dissipating.
Answer: A
2) Galaxies are aggregations of stars, stellar dust, and gas. Their masses
A) are all about the same, which is huge.
B) vary greatly from one galaxy to the next.

C) are small compared to blue supergiant stars.
D) depend on the rate of pulsar emissions within them.
Answer: B
3) Elliptical galaxies
A) tend to be smaller than the other types of galaxies.
B) have little in the way of dust and gas.
C) are thought to be former starburst galaxies.
D) All of the above
Answer: D
4) The Milky Way galaxy is
A) in the process of colliding with the Magellanic Cloud galaxies.
B) where Earth resides.
C) a spiral galaxy.
D) All of the above
Answer: D
5) A Starburst galaxy has this name because of its
A) high rate of star formation.
B) high rate of supernovae.
C) large number of pulsars.
D) large number of neutron stars.
Answer: A
6) An active galactic nucleus

A) is a place of intense star formation.
B) arises from the gigantic black hole at the center of a galaxy.
C) is a supermassive supergiant star that resides at the center of larger galaxies.
D) is a giant dust cloud at the center of a galaxy.
Answer: B
7) Quasars are
A) ancient, extremely high energy galaxies believed to have formed in the early universe.
B) a conglomeration of pulsars within a galaxy.
C) a conglomeration of spiral galaxies.
D) white dwarfs that have undergone final collapse.
Answer: A
8) Our local group is composed of how many galaxies?
A) Less than 100
B) Less than 400
C) Less than 1,000
D) 1,526
Answer: A
9) A supercluster is a
A) cluster of galactic clusters.
B) very large local cluster.
C) local cluster with at least 10,000 supergiant stars.
D) local cluster with at least 500 supermassive black holes.

Answer: A
10) The observable universe is
A) the minor portion of the universe we can observe.
B) the part of the universe that is within the visible electromagnetic spectrum.
C) part of the universe visible to the unaided eye.
D) about 100 billion light years across.
Answer: A
11) All of the stars we see at night with our unaided eyes are within
A) 10,000 light-years, which is a small portion of our galaxy.
B) 100,000 light-years, which encompasses most all of our galaxy.
C) 5 million light-years, which encompasses our local group.
D) 14 billion light-years, which encompasses the observable universe.
Answer: A
12) The Milky Way is
A) a spiral galaxy.
B) an elliptical galaxy.
C) an irregular galaxy.
D) a galaxy in the making.
E) the remains of a galaxy that has run its life course.
Answer: A
13) Most of the stars in colliding galaxies
A) do not make contact with one another.

B) coalesce into larger stars.
C) exchange amounts of material in proportion to their masses.
D) end up as binaries.
E) undergo accelerated collapse.
Answer: A
14) Compared to most stellar objects, quasars are more
A) distant.
B) energetic.
C) puzzling.
D) all of these
E) none of these
Answer: D

Test Bank for Conceptual Physical Science
Paul Hewitt, John Suchocki, Leslie Hewitt
9780321752932, 9780134060491

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