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Astronomy Homework

Question 1

What characteristic of Cepheid variables makes them extremely useful to astronomers?   

· 1.

· The absolute magnitude of Cepheid variables is related directly to their surface

· temperature.

· 2.

· The absolute magnitude of Cepheid variables is directly related to their diameter.

· 3.

· The absolute magnitude of Cepheid variables is related directly to their period of

· pulsation.

· 4.

· The absolute magnitude of Cepheid variables is related directly to their metal

· content (heavy element abundance).

1 points

Question 2

·   What is the most important process that causes a protostar to stop accreting mass?   

· 1.

· 2.

· 3.

· 4.

· All of the infalling matter has been used up in the accretion.

· Radiation and particles from the hot protostar push infalling matter away from

· the protostar.

· Other protostars formed in the vicinity pass randomly through the infalling

· material and eventually disperse it.

· The dense core spins up as it collapses, and eventually the infalling matter is

· held away from the protostar by the centrifugal force.

·  
1 points

Question 3

·   The definition of a main-sequence star is a star   

· 1.

· 2.

· 3.

· 4.

· whose age after birth is about 1 million years.

· with a luminosity precisely equal to that of the Sun.

· in which nuclear fusion reactions generate sufficient energy to oppose further

· condensation of the star.

· with a surface temperature equal to that of the Sun.

·  
1 points

Question 4

·   Which of the following stars would you classify as a Population II star?   

· 1.

· 2.

· 3.

· 4.

· star with approximately the same abundance of heavy elements that we find in the Sun

· star with very low abundance of heavy elements

· star with much higher abundance of heavy elements than we find in the Sun

· star in an open star cluster

·  
1 points

Question 5

·   The light from a distant cloud of gas and dust looks distinctly red to the unaided eye. When a spectrum is taken, the red color is found to come from a single, bright spectral line. Thus the red color in this situation is due to   

· 1.

· 2.

· 3.

· 4.

· interstellar reddening, the Balmer spectrum of hydrogen, or the Doppler effect.

· interstellar reddening.

· the Doppler effect.

· the Balmer spectrum of hydrogen.

·  
1 points

Question 6

·   New stars are formed from   

· 1.

· 2.

· 3.

· 4.

· hot supernova remnants.

· pure energy in free space.

· activity around black holes in the centers of galaxies.

· huge, cool dust and gas clouds.

·  
1 points

Question 7

·   If you were to look at 1 kilogram of material taken from the surface of the Sun and 1 kilogram taken from the center, which of the following statements would be true of the two kilograms?   

· 1.

· 2.

· 3.

· 4.

· Both kilograms have the same amount of hydrogen and are in fact mostly hydrogen.

· The kilogram from the surface contains more hydrogen than the one from the center.

· Neither kilogram contains any hydrogen.

· The kilogram from the surface contains less hydrogen than the one from the center.

·  
1 points

Question 8

·   How is the length of a star’s lifetime related to the mass of the star?   

· 1.

· 2.

· 3.

· 4.

· Lower-mass stars run through their lives faster and have shorter lifetimes.

· Higher-mass stars run through their lives faster and have shorter lifetimes.

· The lifetimes of stars are too long to measure, so it is not known how (or if) their

· lifetimes depend on mass.

· A star’s lifetime does not depend on its mass.

·  
1 points

Question 9

·   How do the stars in a star cluster change with time?   

· 1.

· 2.

· 3.

· 4.

· All stars in a cluster evolve at the same rate.

· The highest-mass stars evolve the most quickly.

· The stars with the greatest heavy element content evolve the most quickly.

· The lowest-mass stars evolve the most quickly.

·  
1 points

Question 10

·   During helium burning in a star’s later life, the chemical element produced by the combination of helium nuclei is   

· 1.

· 2.

· 3.

· 4.

· the light isotope of helium, 3He.

· carbon, 12C.

· heavy hydrogen, 2H.

· beryllium, 8Be.

Question 11

·   What quantum transition occurs inside a hydrogen atom to produce a 21-cm radio photon?   Answer

· 1.

· 2.

· 3.

· 4.

· An electron in the ground atomic state reverses its direction of spin with

· respect to that of the proton.

· An electron falls from the level n = 100 to the level n = 99 in the atom.

· An electron reverses the direction of its motion in orbit around the proton.

· The electron combines with the proton in the nucleus to become a neutron,

· producing energy.

·  
1 points

Question 12

·   What happens when the electron in a hydrogen atom flips its direction of spin from parallel to antiparallel to that of the proton?   Answer

· 1.

· 2.

· 3.

· 4.

· The atom emits a photon of 21-cm wavelength in the radio region of the spectrum.

· The atom emits a photon of 121.5-nm wavelength (Lα) in the UV region of the spectrum.

· Nothing. This event is a forbidden transition that never occurs.

· The atom emits a photon of 656.3-nm wavelength (Hα) in the red region of the spectrum.

·  
1 points

Question 13

·   Why are we on Earth able to see only a relatively small part of the Milky Way Galaxy?   Answer

· 1.

· 2.

· 3.

· 4.

· Distant stars are obscured by dust in interstellar space.

· Expansion of the universe has carried the more distant stars out of our view.

· Distant stars are obscured by gas in interstellar space.

· There are so many stars in the Milky Way that the more distant ones are hidden

· behind the nearer ones.

·  
1 points

Question 14

·   The stars in the Milky Way Galaxy   Answer

· 1.

· 2.

· 3.

· 4.

· number between 8 and 10 million.

· move generally around the galactic center.

· are all receding from the galactic center.

· obey Hubble’s law of recession.

·  
1 points

Question 15

·   Which of the following components of the Milky Way Galaxy outlines the spiral arms of the Galaxy?   Answer

· 1.

· 2.

· 3.

· 4.

· white dwarf stars

· young O and B stars, dust, and gas

· predominantly solar-type stars

· globular clusters

·  
1 points

Question 16

·   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.

· 2.

· 3.

· 4.

· 0%—who ever heard of matter that can’t be seen?

· about

10%

· about 50%

· about 90%

·  
1 points

Question 17

·   Where is the Sun located in the Milky Way Galaxy? (That is, what is the address of the Sun in the universe?) (See Figure 15-9 of Comins and Kaufmann, Discovering the Universe, 8th ed.)   Answer

· 1.

· 2.

· 3.

· 4.

· in the Sagittarius arm, between the Centaurus and Orion arms

· in the Centaurus arm, between the galactic center and the Orion arm

· in or close to the Orion arm, between the Sagittarius and Perseus arms.

· in the Perseus arm, between the Orion and Cygnus arms

·  
1 points

Question 18

·   The first suggestion that there were collections of stars beyond the Milky Way in the universe was made by   Answer

· 1.

· 2.

· 3.

· 4.

· Edwin Hubble in 1923.

· Sir Isaac Newton in 1690.

· William Parsons, Earl of Rosse, in 1845.

· Immanuel Kant in 1755.

·  
1 points

Question 19

·   Where in space would you look for a globular cluster?   Answer

· 1.

· 2.

· 3.

· 4.

· in the asteroid belt

· in elliptical galaxies since they are composed of old stars and do not exist in

· young systems like spiral galaxies

· in the Milky Way galactic halo, orbiting the galactic center in a long elliptical

· orbit around the galactic center

· in the Milky Way disk, moving in a circular orbit around the galactic center

·  
1 points

Question 20

·   Interstellar matter obscures our view of the disk of the Milky Way Galaxy   Answer

· 1.

· 2.

· 3.

· 4.

· most at radio wavelengths, where hydrogen absorbs radio waves efficiently, and

· least at optical wavelengths.

· very little at any wavelength.

· more or less equally at all wavelengths, from radio waves to light waves.

· more at optical wavelengths and less or not at all at infrared and radio wavelengths.

Question 21

·   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   

· 1.

· 2.

· 3.

· 4.

· photon energies are extremely small.

· photons have no rest mass and hence can generate no gravity.

· nature of the photons is such that they interact with nothing as they pass

· through the universe.

· 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.

·  
1 points

Question 22

·   What appears to be the relationship between the distribution of dark matter and the distribution of luminous matter?   

· 1.

· 2.

· 3.

· 4.

· There seems to be no correlation at all.

· The distribution of dark matter seems to coincide with the distribution of luminous

· matter.

· There seems to be a separate distribution of dark matter—dark-matter galaxy

· clusters, voids in the dark matter, and so on. But these formations all occur in

· regions of space far from luminous matter.

· The distribution of dark matter seems to be just the reverse of the distribution of

· luminous matter: Dark-matter galaxy clusters occur in the voids of luminous matter;

· luminous galaxy clusters occur in the voids of dark matter.

·  
1 points

Question 23

·   How does the observed total amount of matter in the universe, including dark matter, compare with the amount of matter required to just close the universe?   

· 1.

· 2.

· 3.

· 4.

· The observed total amount of matter is about twice the amount needed.

· The observed total amount of matter equals the amount needed, to within

· observational uncertainty.

· The observed total amount of matter is about 1/200 of the amount needed.

· The observed total amount of matter is about 1/3 of the amount needed.

·  
1 points

Question 24

·   Which of the following cosmological problems is “dark energy” believed to solve?   

· 1.

· 2.

· 3.

· 4.

· Why did the universe suddenly inflate during the Big Bang?

· Why is the temperature of the cosmic background radiation so smooth (isotropic)

· around the sky?

· Why is the night sky dark?

· Why is the universe flat?

·  
1 points

Question 25

·   What is the range of the strong nuclear force compared with the size of the nucleus, 10–14 m?   

· 1.

· 2.

· 3.

· 4.

· infinite; it has no limit

· 10 times larger than the size of an atomic nucleus

· 10 times smaller than the size of an atomic nucleus

· same since it is the strong force that holds the nucleus together

·  
1 points

Question 26

·   Einstein introduced a “cosmological constant” into his formulation of the structure of the universe as described by his general theory of relativity. How did he envision that this cosmological constant would manifest itself?   

· 1.

· 2.

· 3.

· 4.

· as antimatter that, by annihilating real matter, would translate matter into energy,

· thereby maintaining a constant mass density in a condensing universe

· as a form of energy that, on its own, would make the universe expand—a form of

· antigravity

· as many “white holes” that would contribute matter to an expanding universe to

· maintain constant density, as required by the cosmological principle—a continuous

· creation universe

· as an extra “gravity” that would hold the universe against continuous expansion

·  
1 points

Question 27

·   At what time did the universe cool to a temperature of about 3 K?   

· 1.

· 2.

· 3.

· 4.

· end of the Planck time

· end of the inflationary era

· very recently

· era of recombination

·  
1 points

Question 28

·   What is the period of quark confinement?   

· 1.

· 2.

· 3.

· 4.

· Because of the very large pressure in early times, all the quarks were confined

· to a small volume. After the inflationary, epoch the pressure dropped and the

· quarks were able to spread out to assume the distribution we find today.

· During the period of quark confinement, the energy of the photons was sufficiently

· high that conglomerations of quarks, such as neutrons and protons, could not

· exist and quarks were free.

· to the period of quark confinement was the very early period in the universe when

· all matter and energy were confined to a region the size of a single quark.

· During the period of quark confinement, the energy of the photons was sufficiently

· low that conglomerations of quarks, such as neutrons and protons, could exist

· without being blasted apart as soon as they were formed.

·  
1 points

Question 29

·   During the first one-ten-thousandth of a second (10–4 s) of the life of the universe, antiprotons were very common. For every billion antiprotons, how many protons were there?   

· 1.

· 2.

· 3.

· 4.

· exactly 1 billion since protons and antiprotons were created in equal numbers

· slightly more than 1 billion, thus producing the matter we see today

· 10 billion, thus producing the dark matter we see today

· totally unknown number since the early universe was opaque and we cannot see

· what conditions were like then

·  
1 points

Question 30

·   How does the cosmological constant differ from quintessence?   

· 1.

· 2.

· 3.

· 4.

· There is essentially no difference; basically, quintessence is the modern name for

· the cosmological constant.

· The cosmological constant provides a constant accelerating force in the universal

· expansion, whereas quintessence can change as the expansion proceeds.

· The cosmological constant provides an accelerating force in the universal expansion,

· whereas quintessence provides a decelerating term; it is the balance between the

· cosmological constant and quintessence that determines whether the expansion

· accelerates or decelerates.

· The cosmological constant is a specific physical effect that can be described

· mathematically, whereas quintessence is the total of all indefinable properties

· that make the universe what it is at any given time.

Question 31

·   There is very little hydrogen or helium in the inner part of the solar system today. We believe the reason for this is that   Answer

· 1.

· 2.

· 3.

· 4.

· the intense radiation from the early Sun drove the light elements out of the

· inner solar system.

· all the light elements went into the formation of the Sun itself and little were

· left over for the rest of the solar system.

· heavier elements were attracted in from the outer part of the solar system,

· displacing the light elements originally in the inner part.

· the light elements underwent chemical reactions and were locked up in

· chemicals in the inner solar system.

·  
1 points

Question 32

·   Moons have been discovered around   Answer

· 1.

· 2.

· 3.

· 4.

· just the terrestrial planets.

· just the Jovian planets.

· all the planets.

· all the planets except those nearer to the Sun than Earth is.

·  
1 points

Question 33

·   Each of the following descriptions except one is believed to be a possible mechanism that can trigger the collapse of a cloud of gas and dust to form a star. Which is the exception?   Answer

· 1.

· 2.

· 3.

· 4.

· Stellar winds may compress nearby gas and dust clouds.

· A nearby supernova can compress nearby gas and dust clouds.

· Clouds can collide and compress each other.

· Radiation pressure from the Cosmic Microwave Background can compress

· clouds of gas and dust.

·  
1 points

Question 34

·   The planet whose average density is less than that of water is   Answer

· 1.

· 2.

· 3.

· 4.

· Saturn

· Jupiter

· Neptune

· Earth

·  
1 points

Question 35

·   Which planet in our solar system has the lowest average density?   Answer

· 1.

· 2.

· 3.

· 4.

· Uranus
· Earth
	· Saturn
	· Jupiter

·  
1 points

Question 36

·   How do we measure the mass of an extrasolar planet?   Answer

· 1.

· 2.

· 3.

· 4.

· We cannot make any firm estimate of the mass of an extrasolar planet

· with present technology.

· We measure the planet’s angular diameter and hence its size and then use

· spectra to find its composition and hence density.

· We use Newton’s law of gravity, using the measured distance of the planet

· from its star and the planet’s gravitational pull on the star

· We use spectra to measure the planet’s temperature and photometry to

· measure its brightness.

·  
1 points

Question 37

·   What are the three “common” substances that are believed to be important in planet formation?   Answer

· 1.

· 2.

· 3.

· 4.

· rock, ices, and gas

· electromagnetic radiation, electrical discharges (e.g., lightning), and water

· solid, liquid, and gaseous hydrogen

· hydrogen, helium, and neon gases

·  
1 points

Question 38

·   In our solar system, which of the following planets is a member of the terrestrial group?   Answer

· 1.

· 2.

· 3.

· Saturn

· 4.

· Jupiter

· Neptune

· Mars

·  
1 points

Question 39

·   Pluto was originally classified as a planet, but new criteria for the definition of a planet were adopted, and Pluto failed to meet one of them. Which one?   Answer

· 1.

· 2.

· 3.

· 4.

· Pluto does not have enough gravity to clear its orbit.

· Pluto does not orbit the Sun directly.

· Pluto does not spin fast enough to produce its own magnetic field.

· Pluto does not have enough mass to pull itself into a roughly spherical shape.

·  
1 points

Question 40

·   Which of the following statements is true?   Answer

· 1.

· 2.

· 3.

· 4.

· Earth is the most massive of the terrestrial planets.

· Jupiter has the highest average density of the planets.

· The average mass of terrestrial planets is close to the average mass of the

· large, outer planets.

· Earth is the biggest of the planets.

Question 41

·   The lunar maria appear smooth because they are   Answer

· 1.

· 2.

· 3.

· 4.

· regions where craters have been obliterated by crustal deformation caused by

· hot spots and volcanic lava flow from the underlying molten mantle.

· recent lava flows, occurring within the last billion years, that have obliterated

· earlier craters.

· ancient lava flows that occurred soon after the end of an early period of intense

· bombardment and that have had relatively few impacts since then.

· ancient sea beds, now dry, dating back to when the Moon had a denser

· atmosphere and rainfall was abundant.

·  
1 points

Question 42

·   What is the ratio of nitrogen to oxygen in Earth’s atmosphere?   Answer

· 1.

· 2.

· 3.

· 4.

· equal parts nitrogen and oxygen

· 1 part nitrogen to 4 parts oxygen

· 1 part nitrogen to 2 parts oxygen

· 4 parts nitrogen to 1 part oxygen

·  
1 points

Question 43

·   Which of the following models of Earth’s interior is now considered to be the most likely description of the actual Earth?   Answer

· 1.

· 2.

· 3.

· 4.

· totally fluid interior rotating at the same rate as the outer mantle and crust

· solid core within a molten outer core, the whole system rotating at exactly

· the same rate as the outer mantle and crust

· solid core rotating more rapidly than the rest of Earth within a molten outer core

· solid core rotating more slowly than the rest of Earth within a molten outer core

·  
1 points

Question 44

·   What is the origin of the majority of lunar craters?   Answer

· 1.

· 2.

· 3.

· 4.

· impacts by space probes from Earth

· surface collapse after loss of groundwater by evaporation

· impacts by meteoric material

· volcanic explosions

·  
1 points

Question 45

·   Which scientific approach gives us the most information about the deep interior of Earth?   Answer

· 1.

· 2.

· 3.

· 4.

· worldwide measurement of low-frequency seismic waves produced by earthquakes

· deep drilling of exploratory holes for science and mineral recovery (e.g., oil)

· measurement of cosmic neutrinos, which pass very easily through Earth

· study of lava flows from volcanoes

·  
1 points

Question 46

·   Earth’s mantle, the semimolten layer below the crust, is composed largely of what chemical materials?   Answer

· 1.

· 2.

· 3.

· 4.

· amost pure iron

· minerals rich in iron and magnesium

· solid hydrogen and helium

· iron-poor rocks and minerals

·  
1 points

Question 47

·   What are spring tides?   Answer

· 1.

· 2.

· 3.

· 4.

· high tides that are significantly higher than the average high tide

· high tides that are significantly lower than the average high tide

· any low tides

· any high tides

·  
1 points

Question 48

·   The core (inner and outer) of Earth extends over what fraction of its radius?   Answer

· 1.

· 2.

· 3.

· 4.

· about

· almost 80%

· less than 10%

· roughly

·  
1 points

Question 49

·   Which two tectonic plates are slowly separating from each other on Earth’s surface along the Mid-Atlantic Ridge in the South Atlantic? (See Figure 6-7, Comins and Kaufmann, Discovering the Universe, 8th ed.)   Answer

· 1.

· 2.

· 3.

· 4.

· Pacific and Australia-India plates

· South American and African plates

· African and Eurasian plates

· Nazca and Pacific plates

·  
1 points

Question 50

·   What is the diameter of the Moon compared with the diameter of Earth?   Answer

· 1.

· 2.

· 3.

· 4.

· about 1/10 of the diameter of Earth

· less than 1/100 of the diameter of Earth

· just over 1/2 the diameter of Earth

· about 1/4 of the diameter of Earth

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