Question 1·   The most accurate stellar parallax measurements f.docx

Question 1
· The most accurate stellar parallax measurements for
distances to the majority of stars in our neighborhood of the
universe have been made by Answer
·
· 1.
· the Hubble Space Telescope.
·
· 2.
· the Hipparchos satellite.
·
· 3.
· the Very Long Baseline Array of radio telescopes.
·
· 4.
· Friedrich Wilhelm Bessel, in 1838; no measurements since
then have matched the
· precision of his measurements.
·
2 points
Question 2
· At what time did the universe cool to a temperature of
about 3 K? Answer
·
· 1.
· end of the inflationary era
·
· 2.
· end of the Planck time
·
· 3.
· very recently
·
· 4.

· era of recombination
·
2 points
Question 3
· The present estimate for the Hubble constant is H0 = 71 ±
4 km/s / Mpc. Suppose a galaxy is observed at 3 million
parsecs. If the Hubble law is used to determine its recessional
velocity, what will be the uncertainty? Answer
·
· 1.
· ±225 km/sec
·
· 2.
· ±12 km/sec
·
· 3.
· ±201 km/sec
·
· 4.
· ±284 km/sec
·
2 points
Question 4
· Even though cosmic microwave background photons
outnumber hydrogen atoms by about 1 billion to 1 in the
universe, the universe is still considered to be matter-dominated
because the Answer
·
· 1.
· photons, while collectively carrying a large amount of energy,
do not carry an
· equivalent amount of momentum and hence play little role in
collisions with matter.
·
·
· 2.

· photons have no rest mass and hence can generate no gravity.
·
· 3.
· nature of the photons is such that they interact with nothing as
they pass through
· the universe.
·
·
· 4.
· photon energies are extremely small.
·
2 points
Question 5
· The cosmological redshift of the light from very distant
galaxies is caused by the Answer
·
· 1.
· expansion of space, stretching the photon's wavelength while
the photon is traveling
· toward Earth.
·
·
· 2.
· absorption of blue light by interstellar dust between the Earth
and the galaxy so that
· only the red wavelengths reach the Earth.
·
·
· 3.
· Doppler shift, in which the photon's wavelength is stretched
by the galaxy's motion
· through space, away from Earth, while the photon is being
emitted.
·
·
· 4.

· rotation of the universe around its center (faster at greater
distances from Earth).
·
2 points
Question 6
· A supercluster of galaxies is a Answer
·
· 1.
· cluster of galaxy clusters.
·
· 2.
· cluster of galaxies that is spread out over a larger than normal
volume of space.
·
· 3.
· cluster of galaxies that is packed much more densely than
normal clusters, giving
· it a higher mass.
·
·
· 4.
· phrase describing all the galaxies in the universe as a single
system.
·
2 points
Question 7
· Why would intelligent alien beings wanting to
communicate with us probably choose the 21-cm atomic
hydrogen radio wavelength? Answer
·
· 1.
· This radiation at this particular wavelength is very weak from
natural sources in space,
· and messages would be easily distinguished from other
sources.
·

·
· 2.
· This wavelength shows a very strong Doppler effect when its
source is moving, and
· intelligent alien beings would know that we would be able to
detect the orbital motion
· of their home planet around their star by this method.
·
·
· 3.
· Intelligent alien beings would have detected this particular
wavelength from our
· transmitters on Earth since it is used extensively for satellite
communications,
· and they would know that we could detect them easily.
·
·
· 4.
· Intelligent alien beings would expect that many of our
telescopes would already
· be tuned to this precise wavelength for scientific work.
·
2 points
Question 8
· Which nuclear fusion cycle is the next one to begin after
helium fusion ends in a massive star? Answer
·
· 1.
· carbon fusion
·
· 2.
· silicon fusion
·
· 3.
· iron fusion
·

· 4.
· oxygen fusion
·
2 points
Question 9
· The first 10–43 s of the age of the universe, during which
all four fundamental forces were united, is called
the Answer
·
· 1.
· Hubble time.
·
· 2.
· Planck era.
·
· 3.
· inflationary era.
·
· 4.
· event horizon.
·
2 points
Question 10
· Doppler measurements of the motions of stars in nearby
spiral and barred galaxies indicate that Answer
·
· 1.
· in most spiral and barred galaxies, the arms lead the rotation
of the nucleus; that is,
· the arms spin faster than the nucleus.
·
·
· 2.
· in most spiral and barred galaxies, the arms trail behind the
rotating nucleus.
·

· 3.
· in most spiral and barred galaxies, the arms rotate ahead of the
nucleus; i.e., spiral
· and barred galaxies are mostly leading-arm galaxies.
·
·
· 4.
· about half of all galaxies have trailing arms—the stars rotate
slower than the
· nucleus—while in the other half, the arms rotate ahead of the
nucleus.
·
2 points
Question 11
· Why is it that we will not see fluctuations in light output
in times shorter than about 1 day when we observe an
extragalactic source whose diameter is about 1 light-day?
Answer
·
· 1.
· Arrival times will be different from different parts of the
source, which will smooth
· out short-term fluctuations.
·
·
· 2.
· The light from different parts of the source will be Doppler-
shifted by different
· amounts, allowing us to see only an average shift.
·
·
· 3.
· Absorption of light by intergalactic matter will smooth out
rapid fluctuations
· within the beam.
·

·
· 4.
· It is inconceivable that a source of this size could vary on
such short time scales.
·
2 points
Question 12
· What is the Hubble classification for a spiral galaxy with a
large nuclear region and tightly wound arms? Answer
·
· 1.
· Sc
·
· 2.
· SBc
·
· 3.
· Sb
·
· 4.
· Sa
·
2 points
Question 13
· The spectrum of an ordinary main-sequence star is a
Answer
·
· 1.
· smooth continuum of color, peaking at a specific wavelength
whose position
· depends on the star's surface temperature.
·
·
· 2.
· continuum of colors crossed by dark absorption lines caused
by absorption by

· cooler atoms and molecules at the star's surface.
·
·
· 3.
· continuum of colors, crossed by brighter lines caused by
emission from the hot
· atoms and molecules on the star's surface.
·
·
· 4.
· series of emission lines, mostly from hydrogen, the major
constituent of stellar
· surfaces, that occasionally overlap to produce sections of
continous color.
·
2 points
Question 14
· The forces of gravity and electromagnetism are long-range
forces, extending in principle from their source (mass and
electric charge, respectively) to infinity. Why is it that, in the
universe, only gravity extends to infinity, whereas
electromagnetic forces are much more limited in extent?
Answer
·
· 1.
· Gravity and electromagnetism are one and the same force,
with electromagnetic
· effects extending over limited spatial ranges and transforming
into gravitational
· forces at large distances from matter.
·
·
· 2.
· Electromagnetic forces from positive charges are canceled by
negative charges,
· whereas there are no negative “masses” to cancel the

gravitational force.
·
·
· 3.
· All atoms are electrically neutral, so in reality the
electromagnetic force never
· reaches beyond the size of an atomic nucleus.
·
·
· 4.
· Electromagnetic forces from charged particles will move other
charged particles
· around to produce a uniform charge distribution and therefore
zero electromagnetic
· forces, whereas gravity concentrates mass and enhances the
overall gravity force.
·
2 points
Question 15
· Measurements suggest that light first arrived at Earth from
the Cassiopeia A supernova about 300 years ago and that this
supernova is about 10,000 ly distant from Earth. When did the
explosion actually occur? Answer
·
· 1.
· It is not possible to determine when the explosion occurred
from the information given.
·
· 2.
· 300 years ago, or about A.D. 1700.
·
· 3.
· 9700 years ago, or about 7700 B.C.
·
· 4.
· 10,300 years ago, or about 8300 B.C.

·
2 points
Question 16
· Astronomy with a radio telescope was initiated by
Answer
·
· 1.
· an amateur astronomer, Grote Reber, after Jansky had detected
radio energy from
· the galaxy.
·
·
· 2.
· the British Broadcasting Corporation in England.
·
· 3.
· the National Radio Astronomical Observatories of the United
States, with the
· support of the National Science Foundation and the American
Astronomical Society.
·
·
· 4.
· Marconi in Europe.
·
2 points
Question 17
· The Milky Way is an example of which type of galaxy?
Answer
·
· 1.
· elliptical
·
· 2.
· spiral
·

· 3.
· irregular
·
· 4.
· lenticular, S0 type
·
2 points
Question 18
· Objects with masses between 13 and 75 times the mass of
Jupiter do not fuse hydrogen but do fuse deuterium and lithium
into helium. What do we call such objects? Answer
·
· 1.
· extrasolar planets
·
· 2.
· sub-brown dwarfs
·
· 3.
· red dwarfs
·
· 4.
· brown dwarfs
·
2 points
Question 19
· Evidence for the conclusion that the longer-living gamma-
ray bursters are very distant comes from the Answer
·
· 1.
· delay in the arrival of the visible pulse behind the gamma-ray
pulse, caused by
· the passage of the light through optically thick intergalactic
material.
·
·

· 2.
· spread in arrival times of different gamma-ray photon
energies, indicating a
· long passage through intergalactic gas.
·
·
· 3.
· presence of absorption lines from intergalactic gas clouds in
the spectrum of
· remnant visible light following the gamma-ray burst.
·
·
· 4.
· extreme redshift of emission lines in the visible spectrum
detected after a
· gamma-ray burst.
·
2 points
Question 20
· An astronomer studying a distant galaxy finds that its
recessional velocity is 14,000 km/s. What is the distance to the
galaxy? Assume Hubble's constant to be 70 km/s per Mpc.
Answer
·
· 1.
· 200 Mpc
·
· 2.
· 980,000 Mpc
·
· 3.
· 2000 Mpc
·
· 4.
· 98 Mpc
·

2 points
Question 21
· The Hubble flow, demonstrating the expansion of the
universe, occurs Answer
·
· 1.
· between clusters of galaxies in superclusters and between
superclusters over wider
· ranges of space.
·
·
· 2.
· between stars in galaxies, galaxies in clusters, clusters in
superclusters, and
· superclusters over wider regions of space.
·
·
· 3.
· between galaxies in clusters, clusters in superclusters, and
superclusters in wider
· regions of space.
·
·
· 4.
· only between superclusters of galaxies.
·
2 points
Question 22
· The Tully-Fisher relationship can be used to measure the
luminosity of (and thus the distance to) Answer
·
· 1.
· spiral galaxies.
·
· 2.
· globular clusters.

·
· 3.
· elliptical galaxies.
·
· 4.
· Type II supernovae.
·
2 points
Question 23
· In modern particle physics, the proton and the neutron are
now thought to be composed of more fundamental particles
called Answer
·
· 1.
· neutrinos.
·
· 2.
· photons.
·
· 3.
· quarks.
·
· 4.
· gluons.
·
2 points
Question 24
· Which of the following speeds are described by Hubble's
law? Answer
·
· 1.
· speeds of superclusters of galaxies
·
· 2.
· speeds of individual clusters of galaxies in the Milky Way's
local supercluster

·
· 3.
· speeds of stars in the Milky Way Galaxy
·
· 4.
· speeds of individual galaxies in the Local Group and other
nearby galaxy clusters
·
2 points
Question 25
· Stars in a binary system are useful in studying mass
transfers because we know that the two stars have the same
Answer
·
· 1.
· spectral type.
·
· 2.
· age.
·
· 3.
· mass.
·
· 4.
· radius.
·
2 points
Question 26
· Where do we find supermassive black holes? Answer
·
· 1.
· in the centers of both active and normal galaxies, both nearby
and far away
·
· 2.
· in the centers of both active and normal galaxies, but only

those at relatively high
· redshift values, indicating that they existed in the distant past
·
·
· 3.
· in the centers of giant elliptical galaxies
·
· 4.
· in the centers of active galaxies
·
2 points
Question 27
· The helium flash results from the Answer
·
· 1.
· electron degeneracy or quantum crowding in the core of a low-
mass red giant star.
·
· 2.
· sudden onset of nuclear reactions at the end of the protostar.
·
· 3.
· high temperature in the helium core of a blue (spectral class O
or B) supergiant star.
·
· 4.
· sudden release of energy in strong magnetic fields near a
sunspot.
·
2 points
Question 28
· Why is flatness a problem in cosmology? Answer
·
· 1.
· The total amount of known matter (even if we include dark
matter) is not enough

· to make the universe flat.
·
·
· 2.
· The universe appears to have a hyperbolic geometry to within
observational error,
· yet the universe is expanding, and expanding universes have to
be flat.
·
·
· 3.
· Matter is known to create bumps in the geometry of spacetime;
therefore, the
· universe cannot be flat.
·
·
· 4.
· The universe appears to be flat to within observational error,
yet the universe is
· expanding, and it is impossible for an expanding universe to
be flat.
·
2 points
Question 29
· What name is given to a galaxy with a smooth distribution
of brightness and a round shape? Answer
·
· 1.
· E0
·
· 2.
· SBa
·
· 3.
· E7
·

· 4.
· Sa
·
2 points
Question 30
· An electromagnetic wave leaves the surface of a neutron
star and travels outward. As the wave gets farther from the
star's surface, the _____ and the _____. Answer
·
· 1.
· speed decreases; frequency decreases
·
· 2.
· speed decreases; wavelength increases
·
· 3.
· frequency decreases; wavelength increases
·
· 4.
· frequency increases; wavelength decreases
·
2 points
Question 31
· In the 1970s it was discovered that, among spiral galaxies,
the wider the 21-cm radio emission line, the brighter is the
galaxy. What is the name of this relation? Answer
·
· 1.
· mass-luminosity law
·
· 2.
· Hawking effect
·
· 3.
· Tully-Fisher relation
·

· 4.
· Hubble law
·
2 points
Question 32
· For which one of the following objects has the
phenomenon of differential rotation NOT been
observed? Answer
·
· 1.
· Sun
·
· 2.
· Mars
·
· 3.
· Milky Way Galaxy
·
· 4.
· Jupiter
·
2 points
Question 33
· A planetary nebula is created Answer
·
· 1.
· over several hundred years, during mass transfer in a close
binary star system.
·
· 2.
· in hours or less, during the explosion of a massive star.
·
· 3.
· over a few thousand years or more, in a slow expansion away
from a low-mass star,
· driven by a series of thermal pulses from helium fusion.

·
·
· 4.
· in seconds, during the helium flash in a low-mass star.
·
2 points
Question 34
· What is the most outstanding feature of a quasar compared
with other objects in deep space? Answer
·
· 1.
· great distance from Earth
·
· 2.
· prodigious output of energy
·
· 3.
· small size
·
· 4.
· short lifetime
·
2 points
Question 35
· Quasars emit significant amounts of radiation from the
Lymanα transition. When the spectrum is observed on Earth, it
is found that the Lymanα line is accompanied by many
absorption lines, called the Lymanα forest. What is the origin of
these lines? (See Figure 17-5, Comins and Kaufmann,
Discovering the Universe, 8th ed.) Answer
·
· 1.
· The absorption lines are caused by the rotation of the quasar.
Different parts of
· the quasar thus give rise to Lyman-alpha lines with different
Doppler shifts.

·
·
· 2.
· Because the quasar's jets are aimed at various directions, the
jet plasma has Doppler
· shifts that are different from those of the quasar itself. The
result is a variety of
· Lyman-alpha wavelengths in the spectrum received on Earth.
·
·
· 3.
· The absorption lines are the result of gravitational lensing by
objects between the
· quasar and Earth.
·
·
· 4.
· The emitted Lyman-alpha radiation is absorbed by many gas
clouds between the
· quasar and Earth. The lines are receding at various velocities
and thus are absorbed
· at different Doppler-shifted wavelengths.
·
2 points
Question 36
· In a binary star system, an unseen component is found to
have 8 solar masses. It would be visible if the system were a
normal star, so it must be a collapsed object. Theoretical
considerations tell us that it must be a Answer
·
· 1.
· white dwarf.
·
· 2.
· neutron star.
·

· 3.
· brown dwarf.
·
· 4.
· black hole.
·
2 points
Question 37
· Why is the Coma cluster of galaxies a favorite among
astronomers? Answer
·
· 1.
· The Coma cluster is the cluster in which the Milky Way
Galaxy is situated.
·
· 2.
· The Coma cluster is the rich, regular cluster nearest the Earth.
·
· 3.
· The Coma cluster contains two quasars.
·
· 4.
· The Coma cluster is the rich, irregular cluster nearest the
Earth.
·
2 points
Question 38
· In terms of the evolutionary life of a star, at what stage is
the Crab Nebula? Answer
·
· 1.
· middle-age: main-sequence star, relatively near the Sun
·
· 2.
· black hole: very late stage of evolution
·

· 3.
· late: it is the remnant of a star explosion or supernova
·
· 4.
· beginning: nebula in which stars are forming
·
2 points
Question 39
· A particular galaxy appears round, with a nuclear region of
uniform brightness and an outer region that is broken up into
long, curved, well-defined lanes of stars and light gas clouds.
How would this galaxy be classified? Answer
·
· 1.
· irregular
·
· 2.
· flocculent spiral
·
· 3.
· elliptical
·
· 4.
· grand-design spiral
·
2 points
Question 40
· The “star” that is seen at the center of a planetary nebula
is Answer
·
· 1.
· a planet in the process of formation.
·
· 2.
· the accretion disk around a black hole.
·

· 3.
· composed almost entirely of neutrons and spinning rapidly.
·
· 4.
· a small, hot, and very dense white dwarf star.
·
2 points
Question 41
· The cosmological redshift in the light from distant galaxies
is explained by which of the following effects? Answer
·
· 1.
· The light from more distant galaxies has traveled through the
gravitational fields
· of more galaxies in getting to us and is therefore more
gravitationally redshifted.
·
·
· 2.
· A photon's wavelength is a distance and is therefore
lengthened by the general
· expansion of the universe, making the light appear reddened.
·
·
· 3.
· The light spreads out over larger areas as distance increases
according to 1/(distance)2,
· which causes the wavelength to increase in proportion to
distance.
·
·
· 4.
· The light we on Earth see was Doppler-shifted to longer
wavelengths by the motion of
· the objects (e.g., galaxies) away from Earth.
·

2 points
Question 42
· The first accurate measurement of stellar parallax was
made in Answer
·
· 1.
· 1927.
·
· 2.
· 1721.
·
· 3.
· the fourth century B.C.
·
· 4.
· 1838.
·
2 points
Question 43
· What fraction of the mass of the Milky Way Galaxy
appears to be in the form of “dark matter,” which we cannot see
but can detect through its gravitational influence? Answer
·
· 1.
· about 10%
·
· 2.
· about 90%
·
· 3.
· about 50%
·
· 4.
· 0%—who ever heard of matter that can't be seen?
·
2 points

Question 44
· If a distant cluster were to be composed only of stars with
apparent magnitude of +3, how many stars would there be in
this cluster if its apparent magnitude matched that of a star with
apparent magnitude of +1? Answer
·
· 1.
· 102, or 100
·
· 2.
· 2
·
· 3.
· about 2.5
·
· 4.
· between 6 and 7
·
2 points
Question 45
· Which of the following facts referring to stars in a cluster
is NOT particularly useful for interpreting the evolution of
these stars? Answer
·
· 1.
· The stars formed from the same mix of chemical elements but
with a mix of original
· masses.
·
·
· 2.
· The stars all formed at about the same time.
·
· 3.
· The majority of the material in these stars is hydrogen.
·

· 4.
· The stars are all at the same distance from the Earth, so we
measure true intrinsic
· brightnesses of the stars.
·
2 points
Question 46
· Gas jets have often formed perpendicular to the plane of
the accretion disk around a black hole or a neutron star. What
propels the gas away from the hole or star? Answer
·
· 1.
· enormous pressure of the compressed infalling gas of the
accretion disk
·
· 2.
· strong curvature of spacetime near the object
·
· 3.
· conservation of momentum since the outgoing particles are
pair-produced
· as virtual particles near the object
·
·
· 4.
· magnetic forces from the object's strong magnetic field
·
2 points
Question 47
· The energy required to ionize the hydrogen gas in an
emission nebula (H II region) comes from Answer
·
· 1.
· UV emission from hot O and B stars.
·
· 2.

· collisions between gas clouds in interstellar space.
·
· 3.
· T Tauri stars.
·
· 4.
· supernovae (exploding stars).
·
2 points
Question 48
· Two stars have the same luminosity (or absolute
magnitude). One star is spectral class F and the other is spectral
class K. From this information, we know that the Answer
·
· 1.
· B-type star is larger than the K-type star.
·
· 2.
· K-type star is hotter but can be larger, smaller, or the same
size as the B-type star.
·
· 3.
· B-type star is hotter but can be larger, smaller, or the same
size as the K-type star.
·
· 4.
· K-type star is larger than the B-type star.
·
2 points
Question 49
· The bright stars at the center of an emission nebula (H II
region) are Answer
·
· 1.
· red supergiants.
·

· 2.
· hot white dwarfs.
·
· 3.
· young O and B stars.
·
· 4.
· T Tauri stars.
·
2 points
Question 50
· Which of the following spectral classification letters
signifies the hottest stellar surface temperature? Answer
·
· 1.
· G
·
· 2.
· B
·
· 3.
· A
·
· 4.
· K

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