ASTR 1020: FINAL EXAM
154 Cards in this Set
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If Deneb has an apparent magnitude (seen at the telescope) of 1 and Polaris has an apparent magnitude of 3, the only thing you can conclude is that:
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Deneb appears brighter than Polaris from Earth
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What method might you use to determine the distance to a star?
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Measure the parallax
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Most stars appear to be in the stable hydrogen burning stage like the Sun and are therefore classified as
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Main sequence
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The Hertzsprung-Russell diagram plots _________against temperature.
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Luminosity
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____________ might have masses similar to the Sun, but a radius of nearly 1 AU.
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Red giant stars
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Energy (heat) is transmitted from the core of the Sun to the surface by a combination of:
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Convection and radiation
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These particles are not absorbed within the Sun and allow the only direct observation of conditions in the sun’s core.
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Neutrinos
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Which star is the hottest?
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White dwarfs
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Which star is the most luminous?
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Supergiants
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Which star is the faintest?
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White dwarfs
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Which star is on the Main Sequence?
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Center of main sequence
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Which star has the largest radius?
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Supergiants
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Which star has the smallest radius?
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White dwarfs
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Which star is the most similar to the Sun?
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Main sequence
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The sun is powered by the nuclear fusion of
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Four hydrogen nuclei into one helium nucleus
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What is the average length of the sunspot cycle?
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11 Years
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In general, what physical property of stars can you determine only from binary systems?
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Mass
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You might determine the radius of a star by
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Measuring temperature and luminosity and solving for radius
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Low mass stars live longer than high mass stars
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For main sequence stars, since luminosity and energy consumption increase with mass to the fourth power (approximately), but nuclear fuel only increases with mass to the first power, which of the following is true?
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Betelgeuse is a spectral class M2 star. Lacaille 9352 is also class M2 but is 1,000,000 times fainter than Betelgeuse in absolute luminosity.
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Possible because Betelgeuse has a larger radius than Lacaille
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What factor determines a star's lifetime on the main sequence?
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Its mass
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A main sequence star is in equilibrium because the following are balanced:
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Pressure and gravity
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Betelgeuse is much more luminous than the Sun, yet has a surface temperature one half of the Sun’s. Betelgeuse must be a
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Red supergiant
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Which of the following pair of properties would be most important in determining this reaction rate?
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Density and temperature
Nuclear fusion reactions in stars proceed at a rate determined by how often the particles encounter one another, and the energy of these encounters.
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Two randomly selected stars turn out to have the same apparent brightness in the night sky. Which statement below must be true?
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The farther one emits more energy.
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How many times more luminous than the sun would a star be if it had 3 times the sun’s radius and twice the sun’s temperature?
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Formula: : L= 4πR2σT4
144
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Star shine by convert a portion of its mass into energy. Estimate for the life of star w/2x the sun’s mass & 10x the sun’s rate of energy output?
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Only 1/5 of the sun's lifetime
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Sunspots are dark because
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They are cooler than the surrounding areas
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What is the distance to a star with a parallax of .2"?
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2 Parsecs
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Sunspots, flares, and solar activity in general are tied to changes in the Sun’s
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Magnetic field
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Class O stars are _____________ than class M stars.
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Hotter
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Which of the following poses the greatest danger to communication satellites?
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Solar flares
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How does the position of sunspots appear to change during one sunspot cycle?
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They form closer to the equator as the cycles ages
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What types of star or stars form a nova?
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A white dwarf gaining mass from a red giant companion
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What will ultimately cause this system to become a white dwarf supernova?
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Helium flash
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What, if any, type of remnant object (other than a gas cloud) is left after the explosion?
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None
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What types of star or stars form a massive star supernova?
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A high mass supergiant that has formed an iron core
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What will ultimately cause this system to explode?
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Formation of iron core exceeding Chandrasekhar's limit
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What, if any, type of object (other than a gas cloud) is left after the explosion?
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Neutron star
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White dwarf stars are stable because the gravity is balanced by pressure generated by
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Electron degeneracy
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The Hertzsprung-Russell diagram plots luminosity against ___________.
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Temperature
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A dark cloud, blocking the view of background stars, indicates the presence of interstellar
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Dust
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What event marks the movement of a star onto the main sequence?
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Fusion of hydrogen into helium
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During the horizontal branch stage of a star’s life, helium is fused into
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Carbon
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Which of these life stages will the Sun experience in the distant future?
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Planetary nebula
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What happens inside a star to cause it to leave the main sequence?
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The hydrogen in the core is completely fused to helium
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The hydrogen in the core is completely fused to helium
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Prostar, Main Sequence, Red Supergiant, Supernova, Neutron Star
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Complete the sequence of life stages of a one solar mass star's life in chronological order.
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Prostar, Main Sequence, Red Giant, Planetary Nebula, White Dwarf
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A planetary nebula occurs when a
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A low mass star builds up a carbon core and expels its outer layers
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White dwarf stars have an upper limit of 1.4 solar masses, yet a 2 solar mass main sequence star may ultimately become one. How does it lose mass?
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Ejection of a planetary nebula shell
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What element is the end point of nuclear fusion in the core of a 20 solar mass stars in the supergiant stage?
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Iron
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The most massive elements are created by nuclear fusion in
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High mass stars during a supernova explosion
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An object which begins to form like a star but which has too little mass for hydrogen fusion to ever start is called a
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Brown dwarf
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Stars larger than 150 solar masses are not observed because an object that large would
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Blow itself apart due to high fusion rate and radiation pressure
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How is it possible, then, to find a 2 solar mass main sequence star (star A) orbiting a 1 solar mass red giant (star B)?
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Star B was originally larger and has been losing mass to star A during B's giant stage
Low mass stars evolve more slowly than high mass stars and the giant stage of all stars occurs later in life than main sequence stage.
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Nearly all of the elements found in nature were formed inside stars and supernovas, the exceptions being elements after the creation of the universe:
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Hydrogen and helium
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The typical dust grains in space scatter and absorb the shorter (bluer) wavelengths the best. Result, a star viewed through this dust will appear
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Fainter and redder
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What is a mechanism that could lead to returning heavy elements produced by older stars into the interstellar medium for new star formation?
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Stellar winds
Supernova explosions
Planertary nebulae
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Which of these objects would have the smallest radius?
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A) A 1.0 solar mass white dwarf
B) A 1.0 solar mass main sequence star
C) A 1.0 solar mass red giant star
D) Jupiter
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Which of these objects would have the hottest core?
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A) A .07 solar mass brown dwarf
B) A .5 solar mass main sequence star
C) A 1.0 solar mass main sequence star
D) A 20 solar mass main sequence star
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Which of these objects would have the hottest core?
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A) A .07 solar mass brown dwarf
B) A 1.0 solar mass horizontal branch star
C) A 1.0 solar mass main sequence star
D) A 2.0 solar mass main sequence star
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What would you expect to find if you returned to our solar system in 10 billion years?
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A white dwarf
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Which of these elements had to be made in a supernova explosion?
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Uranium
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Which kinds of stars are most common in a newly formed star cluster?
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Class M stars
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Even though hydrogen fusion in the core has stopped in 1.0 solar mass red giants, the star is still shining. How is it generating that energy?
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Hydrogen fusion in a shell around the core
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The fundamental particles of matter are
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Quarks and leptons
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When an electron is produced by pair creation from two light rays, the following also happens:
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An anti-electron (positron) is also produced
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Within an atomic nucleus, the strongest of the four forces is
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The strong nuclear force
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At distances of one light year, the strongest of the four forces is
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Gravity
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What is the charge on an anti-electron?
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+1
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If you measure a subatomic particle’s position very precisely, then
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Its momentum is highly uncertain
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Which of the following is not allowed by the exclusion principle?
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Having two electrons in the same quantum state
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In which of the following objects is degeneracy pressure the most important force countering gravity?
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A neutron star
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According to modern quantum theory, a vacuum is
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Bubbling with virtual particles popping into and out of existence
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What happens when a proton collides with an anti-proton?
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The annihilate and convert into two light rays
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What is the black body temperature of the microwave background radiation?
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A few Kelvin
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The microwave background radiation falling on the Earth from all directions is now considered to be
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The remains of the radiation created in the Big Bang
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We don’t have an idea of what happened right at the beginning of the Big Bang because
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We don't have a theory of physics that will describe that time
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The early universe was
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Denser and hotter than today
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What events immediately happened after the Big Bang
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Inflation
Pair production and creation of particles
Fusion of quarks into protons, neutrons, and atomic nuclei
Formation of atoms
Formation of stars and galaxies
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Where did the Big Band occur?
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Everywhere, since the Big Bang was the origin of the entire universe
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During the first few seconds after the Big Bang when the universe was very hot, nuclear fusion created
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deuterium
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Which of the following does not provide evidence for the Big Bang Theory?
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Observation of the amount of hydrogen in the universe
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Which of these is the best explanation for why the night sky is dark?
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The universe began less than 14 billion years ago and light from distant objects has not reached us
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Which of these is the best evidence that inflation really happened?
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Observation that the universe looks the same in all directions
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What type of stat is a pulsar?
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Rapidly rotating neutron star
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The region beyond which nothing can escape a black hole is called the
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Event horizon
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To search for a black hole, you would look for
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A binary system w/one invisible star
X-ray emission from an accretion disk in the system
Determination of mass indicates that the unseen star in the binary has a mass greater than about 5 solar masses
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What explanation does General Relativity provide for gravity?
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Gravity is a result of curved spacetime
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Which of the following is unchanging in the Special Theory of Relativity?
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The speed of light
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Carla is traveling past you at a speed close to the speed of light. According to you, while one minute passes for you, how much time passes for her?
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Less than one minute
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Astronomers cannot observe most of the stars in the Milky Way because
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Interstellar dust obscures all but the nearest stars
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The spiral structures of the Milky Way is maintained by
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Density waves
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Galactic evolution is complicated, but a general statement about the evolution of the Milky Way is that
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Small galaxies merged to form the Milky Way
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The youngest stars in the Milky Way are found
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In the spiral arms
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The object located at the center of the Milky Way is believed to be
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A black hole
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What kind of objects lie in the halo of the Milky Way?
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Older, population II stars
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The equivalence principle of General Relativity tells us that effects of these two things are indistinguishable
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Gravity and acceleration
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Which of the following is not a component of the Milky Way?
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Ring
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What makes up the interstellar medium?
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Gas and dust
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What is the Schwarzschild radius of a black hole of 6 solar masses?
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18 kilometers
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What would happen if the Sun suddenly collapsed into a black hole without any change in its mass?
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Earth's orbit would not change
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What is the most likely place in the Milky Way to find an ionization nebula?
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In the spiral arms
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A neutron star consists largely of closely packed neutrons. Therefore the density of a neutron star would be most like the density of
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An atomic nucleus
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How would the stars’ orbital speeds change with distance from the center?
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Stars farther out would have lower speeds
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In the lighthouse model of a pulsar
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If the beams sweep across the Earth, we can observe the pulse
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What compelling evidence links pulsars to neutron stars?
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Only a small, dense source like a neutron star could rotate rapidly without flying apart
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What can escape from inside a black hole's event horizon?
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Nothing
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While perhaps affected by rotation, astronomers think the lower limit for a black hole’s mass is
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3 Solar masses
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The observed slowing of a clock in the vicinity of a black hole is a prediction of:
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General Relativity
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From where do gamma rays bursts appear originate?
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Extremely distant galaxies
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We can deduce where the Sun lies in the Milky Way because
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Globular clusters form a spherical cloud around the Milky Way's center and we lie off-center inside that cloud.
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How can we determine the Milky Way's total mass?
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From the orbital velocities and distances of stars near the edge of the galaxy
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What kind of star is most likely to be part of the spheroidal components of the galaxy?
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A class M star
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Which of these wavelengths of lights allow us to see into the center of the Milky Way?
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Infrared light
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What is the most likely place in the Milky Way to find a globular cluster?
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In the halo
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If you measure a cosmic ray's lifetime you'll find that it is:
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More than one microsecond
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What is a wormhole?
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A shortcut between distant parts of the universe
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Spacetime is
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The combination of time and three dimensions of space
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A galaxy is at a distance of one billion light years. Which of the following is true?
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We see the galaxy the way it was one billion years ago
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In studying the large scale distribution of galaxies, we find that
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Galaxies tend to form groups and clusters
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Hubble used this technique to measure the distance to nearby galaxies
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Cepheid variables
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Why do elliptical galaxies have so few young stars?
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They have little or no coll interstellar gas with which to make stars
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The total number of galaxies is estimated to be
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100 billion
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Which types of galaxies have a clearly defined disk?
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Spirals and lenticulars
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What property is common to all spiral galaxies?
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Ongoing star formation
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Why are Cepheid variables important?
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Their period of variability correlates to their brightness and thus they can be used as a standard candle
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Compared to spiral galaxies, ellipticals tend to have
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No disk components
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What makes white dwarf supernovae good standard candles?
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They all should have approximately the same luminosity
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Why do virtually all of the galaxies in the universe appear to be moving away from our own?
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Because observers in all galaxies would see other galaxies moving away because of the expansion of the universe
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What is the name of the group of galaxies to which the Milky Way belongs?
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Local Group
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Approximately how many galaxies to which the Milky Way belongs?
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Local Group
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What is the Hubble Law?
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The recession velocity of a galaxy is directly proportional to its distance
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Based on the current estimates of the expansion rate of the universe, how old is it?
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Between 12 and 16 billion years
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The two types of spiral galaxies are
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Normal and barred
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Elliptical galaxies are grouped into subclasses based on their
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Shape
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Spiral galaxies are grouped into subclasses based on their
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How tightly the arms are wound and how large their nuclear bulges are
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Irregular galaxies are so named because of their
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Shape
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Which of these factors probably has nothing to do with why some galaxies are spirals and others elliptical?
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Diameter of the protogalactic cloud
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What law does one use to deduce the age of the universe?
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The Hubble Law
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If the geometry of the universe is recollapsing, then the universe
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Will contract some day
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A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of
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Gravitational lensing
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Current understanding suggests that the expansion rate of our universe is
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Accelerating
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Currently, most of the mass (not including energy) of the universe is believed to consist of:
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Dark matter
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Evidence for the presence of dark energy is based on
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White dwarf supernovas being fainter and thus further away than expected
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Dark energy makes up ______ of the total mass/energy in the universe.
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About 70%
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The energy of a quasar is generated in a region approximately the size of
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The solar system
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The power source for an active galactic nucleus is probably
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A super massive black hole with an accretion disk
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Which of the following is not a common factor in active galactic nuclei?
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Most appear to be close to the Milky Way
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What is the primary difference between the light emission from normal and active galaxies?
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Active galaxies emit mostly gamma rays
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Strong evidence for the existence of dark matter comes from observations of
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The motion of galaxies in clusters
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Based on current evidence, which of the following is considered the best candidate for the majority of the dark matter in galaxies?
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Subatomic particles which have not as yet been identified
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What would you expect the rate of supernova explosions to be in a starburst galaxy forming stars 10 times faster than the Milky Way?
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About 10 times higher than the Milky Way
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What age would you expect if the expansion rate in the past had been faster than the present rate?
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Less than 14 billion years
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ASTR 1020: STUDY GUIDE