Astronomy Exam 3

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According to modern science, approximately how old is the Sun?

a) 400 million years
b) 10,000 years
c) 4.5 billion years
d) 25 million years

c) 4.5 billion years

Which of the following correctly describes how the process of gravitational contraction can make a star hot?

a) Heat is generated when gravity contracts, because gravity is an inverse square law force.
b) Gravitational contraction involves nuclear fusion, which generates a lot of heat.
c) When a star contracts in size, gravitational potential energy is converted to thermal energy.
d) Gravitational contraction involves the generation of heat by chemical reactions, much like the burning of coal.

c) When a star contracts in size, gravitational potential energy is converted to thermal energy.

What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?

a) gravitational force and surface tension
b) gravitational force and outward pressure
c) the strong force and the weak force
d) the strong force and the electromagnetic force

b) gravitational force and outward pressure

The source of energy that keeps the Sun shining today is _________.

a) nuclear fission
b) gravitational contraction
c) chemical reactions (fire)
d) nuclear fusion

d) nuclear fusion

Energy balance in the Sun refers to a balance between _________.

a) the mass that the Sun loses each second and the amount of mass converted into energy each second
b) the force of gravity pulling inward and the force due to pressure pushing outward
c) the rate at which fusion generates energy in the Sun’s core and the rate at which the Sun’s surface radiates energy into space
d) the amount of energy the Sun radiates into space and the amount of energy that reaches Earth

c) the rate at which fusion generates energy in the Sun’s core and the rate at which the Sun’s surface radiates energy into space

What are the appropriate units for the Sun’s luminosity?

a) newtons
b) watts
c) kilograms
d) joules

b) watts

The overall result of the proton-proton chain is that __________.

a) 4 H becomes 1 He + energy
b) p + p becomes 2H + energy
c) 6 H becomes 1 He + energy
d) Individual protons are joined into long chains of protons.

a) 4 H becomes 1 He + energy

To estimate the central temperature of the Sun, scientists _________.

a) use computer models to predict interior conditions
b) send probes to measure the temperature
c) use hot gas to create a small Sun in a laboratory
d) monitor changes in Earth’s atmosphere

a) use computer models to predict interior conditions

Solar energy leaves the core of the Sun in the form of

a) photons.
b) rising hot gas.
c) sound waves.

a) photons.

At the center of the Sun, fusion converts hydrogen into

a) plasma.
b) radiation and elements like carbon and nitrogen.
c) helium, energy, and neutrinos.

c) helium, energy, and neutrinos.

Some distinguishing geological characteristics of I0

Io: – volcanoes currently erupting – hot, glowing lava (visible in some photos) – source of ionized gas in the donut-shaped charged particle belt around Jupiter

Some distinguishing geological characteristics of Europa

Europa: – ice covered surface with few impact craters – surface features provide evidence of a subsurface liquid ocean

Some distinguishing geological characteristics of Ganymede

Ganymede: – heavily cratered terrain adjacent to much younger terrain – largest moon in the solar system

Io experiences tidal heating primarily because __________.

a) Io is located very close to Jupiter
b) Io is made of relatively soft materials that deform quite easily
c) Io has an unusually elongated shape that makes it look more like an egg than a sphere
d) Io’s elliptical orbit causes the tidal force on Io to vary as it orbits Jupiter

d) Io’s elliptical orbit causes the tidal force on Io to vary as it orbits Jupiter

From Part A, Io’s elliptical orbit is necessary to its tidal heating. This elliptical orbit, in turn, is a result of the orbital resonance among Io, Europa, and Ganymede. This orbital resonance causes Io to have a more elliptical orbit than it would otherwise, because __________.

a)Io periodically passes Europa and Ganymede in the same orbital position
b) Europa and Ganymede always pull on Io from the same direction as Jupiter pulls on Io
c) Europa and Ganymede are unusually large moons
d) all three moons orbit with the same period, staying aligned at all times

a) Io periodically passes Europa and Ganymede in the same orbital position

We cannot see tidal forces or tidal heating; rather, we predict that they must occur based on the orbital characteristics of the moons. What observational evidence confirms that tidal heating is important on Io?

a) the orbital resonance between Io, Europa, and Ganymede
b) active volcanoes on Io
c) Io’s surprisingly elliptical orbit
d) Io’s unusual, egg-like shape

b) active volcanoes on Io

The orbital resonance also gives Europa an elliptical orbit, so it also experiences tidal heating. However, Europa experiences less tidal heating than Io, because Europa __________ than Io.

a) is more perfectly spherical in shape
b) contains much more ice
c) is much smaller
d) is farther from Jupiter

d) is farther from Jupiter

We now know of many Jupiter-size planets around other stars. Suppose that future observations show that one of these planets has two orbiting moons. What additional information, if any, would we need to decide whether these moons experience tidal heating?

a) We need to know their orbital periods.
b) We need to know whether either moon is volcanically active.
c) We need to know whether the planet also has a third moon.
d) No other information is needed: With two moons, there is sure to be tidal heating.
e) No other information is needed: With two moons, there is no chance of any tidal heating.

a) We need to know their orbital periods.

The largest moon in the solar system is _________.

Ganymede

The jovian moon with the most geologically active surface is ______.

Io

Strong evidence both from surface features and magnetic field data support the existence of a subsurface ocean on ________.

Europa

_________ is responsible for the tremendous volcanic activity on Io

Tidal heating

_________ is the most distant of Jupiter’s four Galilean moons

Callisto

The fact that Europa orbits Jupiter twice for everyone orbit of Ganymede is an example of an __________.

Orbital Resonance

The main ingredients of most satellites of the jovian planets are

a) rock and metal.
b) hydrogen compound ices.
c) hydrogen and helium.

b) hydrogen compound ices.

Why is Io more volcanically active than our moon?

a) Io is much larger.
b) Io has a higher concentration of radioactive elements.
c) Io has a different internal heat source.

c) Io has a different internal heat source.

Saturn’s many moons affect its rings through

a) tidal forces.
b) orbital resonances.
c) magnetic field interactions.

b) orbital resonances.

These two moons orbit Saturn at 139350 (Prometheus) and 141700 (Pandora) kilometers, respectively.

Using Newton’s version of Kepler’s third law, find orbital period of Prometheus.

Tprometheus = 14.7 hr

These two moons orbit Saturn at 139350 (Prometheus) and 141700 (Pandora) kilometers, respectively.

Using Newton’s version of Kepler’s third law, find orbital period of Pandora.

Tpandora = 15.1 hr

These two moons orbit Saturn at 139350 (Prometheus) and 141700 (Pandora) kilometers, respectively.

Find the percent difference in their distances.

(dpandora−dprometheus)/(dpandora) = 1.66 %

These two moons orbit Saturn at 139350 (Prometheus) and 141700 (Pandora) kilometers, respectively.

Find the percent difference in their orbital periods.

(Tpandora−Tprometheus)/(Tpandora) = 2.6 %

These two moons orbit Saturn at 139350 (Prometheus) and 141700 (Pandora) kilometers, respectively.

Consider the two in a race around Saturn: In one Prometheus orbit, how far behind is Pandora (in units of time)?

0.4 hr

These two moons orbit Saturn at 139350 (Prometheus) and 141700 (Pandora) kilometers, respectively.

In how many Prometheus orbits will Pandora have fallen behind by one of its own orbital periods? Convert this number of periods back into units of time. This is how often the satellites pass by each other.

23.1 days

Using the data in the table Satellites of the Solar System in the textbook, identify the orbital resonance relationship between Titan and Hyperion. (Hint: If the orbital period of one were 1.5 times the other, we would say that they are in a 3:2 resonance.)

a) 2:1
b) 3:2
c) 4:3
d) 5:4

c) 4:3

Which medium-size moon is in a 2:1 resonance with Enceladus?

a) Tethys
b) Rhea
c) Dione
d) Mimas

c) Dione

Saturn’s rings are composed of __________.

a) gas from the early solar system
b) a series of solid concentric circles
c) lots of individual particles of ice and rock
d) parts of Saturn’s upper atmosphere being vented into space

c) lots of individual particles of ice and rock

Saturn’s rings look bright because __________.

a) light from the Sun reflects off the material in the rings
b) the material in the rings is hot and creates its own light
c) light from Saturn reflects off the material in the rings

a) light from the Sun reflects off the material in the rings

Which of the following statements correctly describes the motion of the particles in Saturn’s rings?

a) Particles in all the rings hover motionlessly high above Saturn.
b) Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings.
c) Particles in the inner rings orbit Saturn at a slower speed than particles in the outer rings.
d) All the particles in the rings orbit Saturn with the same orbital period.

b) Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings.

Each ring particle in the densest part of Saturn’s rings collides with another about every 5 hours.

If a ring particle survived for the age of the solar system, how many collisions would it undergo?

N = 8×10^12 collisions

What causes synchronous rotation?

a) orbital resonances with other moons
b) A massive planet exerts a tidal force on a moon that causes the moon to obtain the same rotational period as its parent planet.
c) Most jovian moons were formed out of their planet’s nebula with the same rotational period as their parent planet.
d) A massive planet exerts a tidal force on a moon that causes the moon to align itself such that its tidal bulges always point toward and away from the planet.
e) Most jovian moons were formed out of their planet’s nebula with the same orbital period.

d) A massive planet exerts a tidal force on a moon that causes the moon to align itself such that its tidal bulges always point toward and away from the planet.

What is the Cassini division of Saturn’s rings?

a) the most opaque ring of Saturn, made of highly reflective ice particles
b) a dark ring, visible from Earth, composed of dark, dusty particles
c) the widest ring of Saturn, located between two large ring gaps
d) the imaginary circle marking the halfway point of Saturn’s rings
e) a large gap, visible from Earth

e) a large gap, visible from Earth

Which of the following statements about the rings of the four jovian planets is not true?

a) All have gaps and ringlets, probably due to gap moons, shepherd moons, and orbital resonances.
b) All the particle orbits are fairly circular, near their planet’s equatorial plane.
c) All probably look much like they did when the solar system first formed.
d) All are made of individual particles of rock or ice that orbit in accord with Kepler’s laws: inner ring particles orbiting faster, and outer ring particles orbiting slower.
e) All rings lie within their planet’s Roche zone.

c) All probably look much like they did when the solar system first formed.

What mechanism is most responsible for generating the internal heat of Io that drives the volcanic activity?

a) radioactive decay
b) accretion
c) differentiation
d) bombardment
e) tidal heating

e) tidal heating

The four Galilean moons around Jupiter are

a) very similar to asteroids.
b) hydrogen and helium gas.
c) a mixture of rock and ice.
d) all made of ice.
e) all made of rock.

c) a mixture of rock and ice.

Did a large terrestrial planet ever form in the region of the asteroid belt?

a) No, because there was never enough mass there.
b) No, because Jupiter prevented one from accreting.
c) Yes, but it was shattered by a giant impact.

b) No, because Jupiter prevented one from accreting.

The asteroid belt lies between the orbits of

a) Earth and Mars.
b) Mars and Jupiter.
c) Jupiter and Saturn.

b) Mars and Jupiter.

A comet entering the inner solar system from afar will __________.

a) form a tail and some time later form a coma.
b) form a coma and some time later form a tail
c) always form a tail, but only sometimes form a coma

b) form a coma and some time later form a tail

During the time that a comet passes through the inner solar system, the comet can appear quite bright because __________.

a) heat from the Sun causes the comet’s nucleus to glow
b) increasing friction causes the comet’s nucleus to glow
c) sunlight reflects off the comet’s tail and coma
d) sunlight reflects off the comet’s nucleus

c) sunlight reflects off the comet’s tail and coma

A comet’s plasma tail always points directly away from the Sun because __________.

a) of pressure exerted by the fast-moving charged particles in the solar wind
b) centrifugal forces throw the tail outward as the comet travels around the Sun
c) the comet’s nucleus overheats on the Sun-facing side, forcing energetic jets of gas to shoot out from the dark side
d) the tail is left behind as the comet moves through its orbit

a) of pressure exerted by the fast-moving charged particles in the solar wind

About a trillion comets are thought to be located far, far beyond Pluto in the ________.

Oort Cloud

The bright spherical part of a comet observed when it is close to the Sun is the _____.

Coma

A comet’s ___________ stretches directly away from the Sun

Plasma Tail

A comet’s _______ is the frozen portion of a comet

Nucleus

Particles ejected from a comet can cause a ________ on Earth

Meteor Shower

The ___________ extends from about beyond the orbit of Neptune to about twice the distance of Neptune from the Sun

Kuiper Belt

How does the largest asteroid, Ceres, compare in size to other solar system worlds?

a) It is about a quarter the size of the Moon.
b) It is about the size of Pluto.
c) It is about the size of a large jovian moon.
d) It is larger than Pluto and Mercury.
e) It is smaller than any jovian moon.

a) It is about a quarter the size of the Moon.

Which is closest to the average distance between asteroids in the asteroid belt?

a) 10 thousand km
b) 100 thousand km
c) 1 thousand km
d) 1 million km
e) 10 million km

d) 1 million km

Where are the Trojan asteroids located?

a) in the center of the asteroid belt
b) on orbits that cross Mars’s orbit
c) on orbits that cross Earth’s orbit
d) along Jupiter’s orbit, 60° ahead of and behind Jupiter
e) surrounding Jupiter

d) along Jupiter’s orbit, 60° ahead of and behind Jupiter

We know that there are large gaps in the average distances of asteroids from the Sun (within the asteroid belt) because we

a) actually don’t know whether there really are gaps or not.
b) have plotted distributions of the orbital radii of the asteroids.
c) know they are there theoretically, although we haven’t detected them.
d) see the gaps through telescopes.
e) see the gaps via stellar occultation.

b) have plotted distributions of the orbital radii of the asteroids.

If we know the size of an asteroid, we can determine its density by

a) looking for brightness variations as it rotates.
b) radar mapping.
c) determining its mass from its gravitational pull on a spacecraft, satellite, or planet.
d) comparing its reflectivity to the amount of light it reflects.
e) spectroscopic imaging.

c) determining its mass from its gravitational pull on a spacecraft, satellite, or planet.

What part of a comet points most directly away from the Sun?

a) the coma
b) the plasma tail
c) the nucleus
d) the dust tail
e) the jets of gas

b) the plasma tail

When do comets generally begin to form a tail?

a) inside Mercury’s orbit
b) They always have a tail (until they run out of material).
c) between Mercury and Earth’s orbit
d) inside of Jupiter’s orbit
e) beyond Jupiter’s orbit

d) inside of Jupiter’s orbit

Where did comets that are now in the Kuiper belt originally form?

a) in the Oort cloud
b) inside Jupiter’s orbit
c) near the radius at which they orbit today
d) in the asteroid belt
e) between the orbits of Jupiter and Neptune

c) near the radius at which they orbit today

Where did comets that are now in the Oort cloud originally form?

a) inside Jupiter’s orbit
b) within the solar nebula, but far outside the orbit of Pluto
c) near the jovian planets
d) outside Neptune’s orbit
e) all of the above

c) near the jovian planets

What is the typical size of comets that enter the inner solar system?

a) 1 km
b) 10 km
c) 100 km
d) Comet sizes are unknown because their tails obscure the nucleus.
e) 1000 km

b) 10 km

The total amount of power (in watts, for example) that a star radiates into space is called its _________.

a) luminosity
b) flux
c) apparent brightness
d) absolute magnitude

a) luminosity

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

a) Its apparent brightness will decrease by a factor of 9.
b) Its apparent brightness will increase by a factor of 9.
c) Its apparent brightness will decrease by a factor of 3.
d) Its apparent brightness will increase by a factor of 3.

a) Its apparent brightness will decrease by a factor of 9.

Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?

a) determine the distance to the star from its apparent brightness
b) calculate the star’s luminosity if we know its distance, or calculate its distance if we know its luminosity
c) determine both the star’s distance and luminosity from its apparent brightness
d) calculate the star’s surface temperature if we know either its luminosity or its distance

b) calculate the star’s luminosity if we know its distance, or calculate its distance if we know its luminosity

If star A is closer to us than star B, then Star A’s parallax angle is _________.

a) larger than that of Star B
b) hotter than that of Star B
c) smaller than that of Star B
d) fewer parsecs than that of Star B

a) larger than that of Star B

Which of these stars is the most massive?

a) a main-sequence A star
b) a main-sequence G star
c) a main-sequence M star

a) a main-sequence A star

From hottest to coolest, the order of the spectral types of stars is _________.

a) OBAGFKM
b) OBAFGKM
c) ABFGKMO
d) ABCDEFG
e) OMKGFBA

b) OBAFGKM

Astronomers can measure a star’s mass in only certain cases. Which one of the following cases might allow astronomers to measure a star’s mass?

a) The star is of spectral type A.
b) We know the star’s luminosity and distance.
c) The star is of spectral type G.
d) The star is a member of a binary star system.

d) The star is a member of a binary star system.

The axes on a Hertzsprung-Russell (H-R) diagram represent _________.

a) luminosity and surface temperature
b) mass and radius
c) mass and luminosity
d) luminosity and apparent brightness

a) luminosity and surface temperature

On an H-R diagram, stellar radii _________.

a) are greatest in the lower left and least in the upper right
b) are impossible to determine
c) increase diagonally from the lower left to the upper right
d) decrease from left to right

c) increase diagonally from the lower left to the upper right

On an H-R diagram, stellar masses _________.

a) can be estimated for main sequence stars but not for other types of stars
b) are impossible to determine
c) increase from upper left to lower right
d) are greatest in the lower left and least in the upper right

a) can be estimated for main sequence stars but not for other types of stars

How is the lifetime of a star related to its mass?

a) More massive stars live slightly shorter lives than less massive stars.
b) More massive stars live slightly longer lives than less massive stars.
c) More massive stars live much shorter lives than less massive stars.
d) More massive stars live much longer lives than less massive stars.

c) More massive stars live much shorter lives than less massive stars.

What is the common trait of all main sequence stars?

a) They are all spectral type G.
b) They are in the final stage of their lives.
c) They generate energy through hydrogen fusion in their core.
d) They all have approximately the same mass.

c) They generate energy through hydrogen fusion in their core.

Which of these layers of the Sun is coolest?

a) photosphere
b) chromosphere
c) corona

a) photosphere

Which of these layers of the Sun is coolest?

a) core
b) radiation zone
c) photosphere

c) photosphere

The total annual U.S. energy consumption is about 2×1020 joules.

What is the average power requirement for the United States, in watts? (Hint: 1 watt = 1 joule/s)

Paverage = 6.34×10^12 W

The total annual U.S. energy consumption is about 2×1020 joules.

With current technologies and solar collectors on the ground, the best we can hope for is that solar cells will generate an average (day and night) power of about 230watts/m2 . What total area would we need to cover with solar cells to supply all the power needed for the United States? Give your answer in both square meters and square kilometers.

Atotal = 2.76×10^10 m^2 Atotal = 2.76×10^4 km^2

Listed following are the different layers of the Sun. Rank these layers based on their distance from the Sun’s center, from greatest to least.

Photosphere
Core
Corona
Convection Zone
Chromosphere
Radiation Zone

Corona Chromosphere Photosphere Convection Zone Radiation Zone Core

Rank the layers of the Sun based on their density, from highest to lowest.

Photosphere
Core
Corona
Convection Zone
Chromosphere
Radiation Zone

Core Radiation Zone Convection Zone Photosphere Chromosphere Corona

Rank the following layers of the Sun based on their temperature, from highest to lowest.

Photosphere
Core
Convection Zone
Radiation Zone

Core Radiation Zone Convection Zone Photosphere

Rank the following layers of the Sun based on the pressure within them, from highest to lowest.

Photosphere
Core
Convection Zone
Radiation Zone

Core Radiation Zone Convection Zone Photosphere

In which of the following layer(s) of the Sun does nuclear fusion occur?

Photosphere
Core
Corona
Convection Zone
Chromosphere
Radiation Zone

Core

Which of the following layers of the Sun can be seen with some type of telescope? Consider all forms of light, but do not consider neutrinos or other particles.

Photosphere
Core
Corona
Convection Zone
Chromosphere
Radiation Zone

Photosphere Corona Chromosphere

Nuclear fusion of hydrogen into helium occurs in the ______.

Core

Energy moves through the Sun’s ________ by means of the rising of hot gas and falling of cooler gas.

Convection Zone

Nearly all the visible light we see from the Sun is emitted from the ________.

Photosphere

Most of the Sun’s ultraviolet light is emitted from the narrow layer called the __________ where temperature increases with altitude.

Chromosphere

We can see the Sun’s ______ most easily during total eclipses.

Corona

The ___________ is the layer of the Sun between its core and convection.

Radiation Zone

From center outward, which of the following lists the "layers" of the Sun in the correct order?

a) core, convection zone, radiation zone, corona, chromosphere, photosphere
b) core, radiation zone, convection zone, photosphere, chromosphere, corona
c) core, radiation zone, convection zone, corona, chromosphere, photosphere
d) core, corona, radiation zone, convection zone, photosphere, chromosphere

b) core, radiation zone, convection zone, photosphere, chromosphere, corona

Which of these groups of particles has the greatest mass?

a) a helium nucleus with two protons and two neutrons
b) four electrons
c) four individual protons

c) four individual protons

Scientists estimate the central temperature of the Sun using

a) probes that measure changes in Earth’s atmosphere.
b) mathematical models of the Sun.
c) laboratories that create miniature versions of the Sun.

b) mathematical models of the Sun.

Which of the following changes would cause the fusion rate in the Sun’s core to increase?

a) An increase in the core temperature
b) An increase in the core radius
c) A decrease in the core temperature
d) A decrease in the core radius

a) An increase in the core temperature & d) A decrease in the core radius

Which of the following must occur for a star’s core to reach equilibrium after an initial change in fusion rate?

a) If the fusion rate initially decreases, then the core expands.
b) If the fusion rate initially increases, then the core expands.
c) If the fusion rate initially decreases, then the core contracts.
d) If the fusion rate initially increases, then the core contracts.

b) If the fusion rate initially increases, then the core expands. & c) If the fusion rate initially decreases, then the core contracts.

What would happen if the fusion rate in the core of the Sun were increased but the core could not expand?

a) The Sun’s core would start to cool down and the rate of fusion would decrease.
b) The Sun’s core would reach a new equilibrium at a lower temperature.
c) The Sun’s core would reach a new equilibrium at a higher temperature.
d) The Sun’s core would start to heat up and the rate of fusion would increase even more.

d) The Sun’s core would start to heat up and the rate of fusion would increase even more.

How is the sunspot cycle directly relevant to us here on Earth?

a) The sunspot cycle strongly influences Earth’s weather.
b) Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment.
c) The sunspot cycle is the cause of global warming.
d) The Sun’s magnetic field, which plays a major role in the sunspot cycle, affects compass needles that we use on Earth.
e) The brightening and darkening of the Sun that occurs during the sunspot cycle affects plant photosynthesis here on Earth.

b) Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment.

Why do sunspots appear darker than their surroundings?

a) They are cooler than their surroundings.
b) They block some of the sunlight from the photosphere.
c) They do not emit any light.

a) They are cooler than their surroundings.

What is the most common kind of element in the solar wind?

a) hydrogen
b) carbon
c) helium

a) hydrogen

Which of these things poses the greatest hazard to communications satellites?

a) photons from the Sun
b) solar magnetic fields
c) protons from the Sun

c) protons from the Sun

Based on its surface temperature of 5,800 K, what color are most of the photons that leave the Sun’s surface?

a) red
b) orange
c) green
d) yellow
e) blue

c) green

How much mass does the Sun lose through nuclear fusion per second?

a) 600 tons
b) 4 tons
c) 600 million tons
d) Nothing: mass is conserved.
e) 4 million tons

e) 4 million tons

Suppose you put two protons near each other. Because of the electromagnetic force, the two protons will

a) attract each other.
b) join together to form a nucleus.
c) repel each other.
d) remain stationary.
e) collide.

c) repel each other.

Which is the strongest of the fundamental forces in the universe?

a) gravitational force
b) strong force
c) weak force
d) electromagnetic force
e) none of the above

b) strong force

Suppose that, for some unknown reason, the core of the Sun suddenly became hotter. Which of the following best describes what would happen?

a) Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal.
b) The higher temperature would not affect the fusion rate but would cause the core to expand and cool until the temperature returned to normal, with the core at a new, slightly larger size.
c) Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and turn the Sun into a giant star.
d) Higher temperature would cause the rate of fusion to fall, decreasing the internal pressure and causing the core to collapse until the rate of fusion returned to normal.

a) Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal.

The light radiated from the Sun’s surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about

a) a hundred years ago.
b) one year ago.
c) a million years ago.
d) a thousand years ago.
e) ten years ago.

c) a million years ago.

What processes are involved in the sunspot cycle?

a) the winding of magnetic field lines due to differential rotation
b) the interaction of the Earth’s magnetic field with that of the Sun
c) wave motions in the solar interior
d) variations of the solar thermostat
e) gravitational contraction of the Sun

a) the winding of magnetic field lines due to differential rotation

Which of the following statements about the sunspot cycle is not true?

a) The rate of nuclear fusion in the Sun peaks about every 11 years.
b) The cycle is truly a cycle of magnetic activity, and variations in the number of sunspots are only one manifestation of the cycle.
c) The number of sunspots peaks approximately every 11 years.
d) With each subsequent peak in the number of sunspots, the magnetic polarity of the Sun is the reverse of the previous peak.
e) The number of solar flares peaks about every 11 years.

a) The rate of nuclear fusion in the Sun peaks about every 11 years.

Sunspots are cooler than the surrounding solar surface because:

a) strong magnetic fields slow convection and prevent hot plasma from entering the region.
b) they are regions where convection carries cooler material downward.
c) magnetic fields lift material from the surface of the Sun, cooling off the material faster.
d) there is less fusion occurring there.
e) magnetic fields trap ionized gases that absorb light.

a) strong magnetic fields slow convection and prevent hot plasma from entering the region.

What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?

a) the time between eclipses and the average distance between the stars
b) the period of the binary system and its distance from the Sun
c) the velocities of the stars and the Doppler shifts of their absorption lines

a) the time between eclipses and the average distance between the stars

Which of these stars has the coolest surface temperature?

a) an A star
b) an F star
c) a K star

c) a K star

Alpha Centauri A lies at a distance of 4.4 light-years and has an apparent brightness in our night sky of 2.7×10^−8 watt/m2. Recall that 1 lightyear = 9.5×10^12 km = 9.5×10^15 m.

Use the inverse square law for light to calculate the luminosity of Alpha Centauri A.

L = 5.9×10^26 watts

Use the inverse square law for light

Suppose a star has the same luminosity as our Sun (3.8×10^26 watts) but is located at a distance of 15 light−years . What is its apparent brightness?

F = 1.5×10^−9 watts/m2

Use the inverse square law for light

Suppose a star has the same apparent brightness as Alpha Centauri A (2.7×10^−8 watt/m^2) but is located at a distance of 200 light−years . What is its luminosity?

L = 1.2×1030 watts

Use the inverse square law for light

Suppose a star has a luminosity of 6.0×10^26 watts and an apparent brightness of 4.5×10^−12 watt/m^2 . How far away is it? Give your answer in both kilometers and light-years.

d = 3.3×10^15 km d = 340 light−years

Use the inverse square law for light

Suppose a star has a luminosity of 5.0×10^29 watts and an apparent brightness of 6.0×10^−15 watt/m^2 . How far away is it? Give your answer in both kilometers and light-years.

d = 2.6×10^18 km d = 2.7×10^5 light−years

Use the parallax formula to calculate the distance to each of the following stars. Give your answers in both parsecs and light-years.

Alpha Centauri: parallax angle 0.7420”

d = 1.348 pc d = 4.396 light−years

Use the parallax formula to calculate the distance to each of the following stars. Give your answers in both parsecs and light-years.

Procyon: parallax angle of 0.2860”

d = 3.497 pc d = 11.40 light−years

Sirius A has a luminosity of 26 LSun and a surface temperature of about 9400 K

What is its radius? (Hint: See Mathematical Insight Calculating Stellar Radii.)

R = 1.3×10^9 m

Before we can use parallax to measure the distance to a nearby star, we first need to know __________.

a) the Sun’s mass
b) the distance to the nearest star besides the Sun
c) the month in which the star is observed
d) the Earth-Sun distance

d) the Earth-Sun distance

Which of the following is a valid way of demonstrating parallax for yourself?

a) Get a camera, and photograph a person who is running back and forth.
b) Look up at a star, and notice how it moves toward the western horizon during the night.
c) Hold up your hand in front of your face, and move it slowly back and forth.
d) Hold up your hand in front of your face, and alternately close your left and right eyes.

d) Hold up your hand in front of your face, and alternately close your left and right eyes.

What is the cause of stellar parallax?

a) the gradual motion of stars in the local solar neighborhood.
b) Earth’s orbit around the Sun.
c) the gradual change in the patterns of the constellations over thousands of years.
d) the varying speed of Earth in its orbit around the Sun.

b) Earth’s orbit around the Sun.

The more distant a star, the __________.

a) faster its parallax occurs
b) slower its parallax occurs
c) larger its parallax angle
d) smaller its parallax angle

d) smaller its parallax angle

Approximately what is the parallax angle of a star that is 20 light-years away?

a) 0.0072 arcsecond
b) 4.5×10−5 arcsecond
c) 0.16 arcsecond
d) 0.33 arcsecond

c) 0.16 arcsecond parallax formula: d(in light-years)=3.26×(1/p(in arcseconds)) or p(in arcseconds)=3.26×(1/d(in light-years))

Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?

a) 1 light-year
b) 2.1 light-years
c) 8.7 light-years
d) 3.3 light-years

d) 3.3 light-years

How can we determine the reflectivity of an asteroid?

a) by where it is located in the asteroid belt
b) by comparing its brightness in visible light to its brightness in infrared light
c) by taking a photograph of it
d) by measuring its mass and radius

b) by comparing its brightness in visible light to its brightness in infrared light

How does the Sun generate energy today?

a) gravitational contraction
b) nuclear fusion
c) nuclear fission
d) gradually expanding in size
e) chemical reactions

b) nuclear fusion

We know that there are large gaps in the average distances of asteroids from the Sun (within the asteroid belt) because we

a) see the gaps through telescopes
b) see the gaps via stellar occultation
c) know they are there theoretically, although we haven’t detected them
d) have plotted distributions of the orbital radii of the asteroids
e) actually don’t know whether there are really are gaps

d) have plotted distributions of the orbital radii of the asteroids

When do comets generally begin to form a tail?

a) inside Mercury’s orbit
b) beyond Jupiter’s orbit
c) inside of Jupiter’s orbit
d) between Mercury and Earth’s orbit
e) they always have a tail (until they run out of material)

c) inside of Jupiter’s orbit

The overall fusion reaction by which the Sun currently produces energy is

a) 4H => 4He + energy
b) 6H => 1He + energy
c) 3H => 1Li + energy
d) 3He => 1C + energy
e) 4H => 1He + energy

e) 4H => 1He + energy

The combined mass of all the asteroids in the asteroid belt is

a) about the same as that of Jupiter
b) about twice that of Earth
c) more than that of all the planets combined
d) less than that of any terrestrial planet
e) about the same as that of Earth

d) less than that of any terrestrial planet

What causes synchronous rotation?

a) a massive planet exerts a tidal force on a moon that causes the moon to align itself such that its tidal bulges always point toward and away from the planet
b) most jovian moons were formed out of their planet’s nebula with the same rotational period as their parent planet
c) most jovian moons were formed out of their planet’s nebula with the same orbital period
d) a massive planet exerts a tidal force on a moon that causes the moon to obtain the same rotational period as its parent planet

a) a massive planet exerts a tidal force on a moon that causes the moon to align itself such that its tidal bulges always point toward and away from the planet

When a comet passes near the Sun, part of it takes on the appearance of a large, bright ball from which the tail extends. This part is called

a) the Oort core
b) the plasma tail
c) the nucleus
d) the coma

d) the coma

Which of the following statements correctly describes the motion of the particles of Saturn’s rings?

a) all the particles in the rings orbit Saturn with the same orbital period
b) particles in the outer rings orbit Saturn at a slower speed than particles in the inner rings
c) particles in all the rings hover motionlessly above Saturn
d) particles in the outer rings orbit Saturn at a faster speed than particles in the inner rings

b) particles in the outer rings orbit Saturn at a slower speed than particles in the inner rings

What is responsible for the Cassini division in Saturn’s rings?

a) any particle that would orbit in the Cassini division would be in orbital resonance with Saturn
b) there is a gap moon, Pan, inside the Cassini division, which sweeps any particles out of the division
c) the shepherd moons Pandora and Prometheus orbit just outside and just inside, respectively, of the Cassini division, and they sweep any particles out of the division
d) any particle that would orbit in the Cassini division would be in the Roche tidal zone of Saturn
e) any particle that would orbit in the Cassini division would be in orbital resonance with Mimas

e) any particle that would orbit in the Cassini division would be in orbital resonance with Mimas

Why does the plasma tail of a comet always point away from the sun?

a) the conservation of the angular momentum of the tail keeps it always pointing away from the Sun
b) gases from the comet, heated by the Sun push the tail away from the Sun
c) it is allergic to sunlight
d) the solar wind electromagnetically "blows" the ions directly away from the Sun
e) radiation pressure from the Sun’s light pushes the ions away

d) the solar wind electromagnetically "blows" the ions directly away from the Sun

All of the following statements are true. Which one is most important in explaining the tremendous tidal heating that occurs on Io?

a) Io is the closest to Jupiter of Jupiter’s large moons
b) Io is the third largest Galilean satellite
c) Io orbits Jupiter on an elliptical orbit, due to orbital resonances with other satellites
d) Io exhibits synchronous rotation, meaning that its rotation period and orbital period are the same

c) Io orbits Jupiter on an elliptical orbit, due to orbital resonances with other satellites

Which is closest to the temperature of the core of the Sun?

a) 10 million K
b) 1 million K
c) 10,000 K
d) 100 million K
e) 100,000 K

a) 10 million K

Which of the following statements about the Roche tidal zone is true?

a) it is the region of space within 2-3 radii of any planet, where the tidal force from the planet would be strong enough to tear apart any object which is held together by its own gravity
b) the Sun does not possess a Roche tidal zone
c) the Moon is located within the Earth’s Roche tidal zone
d) It’s only the region of space within which all Jovian planets’ rings are located; the terrestrial planets do not possess a Roche tidal zone

a) it is the region of space within 2-3 radii of any planet, where the tidal force from the planet would be strong enough to tear apart any object which is held together by its own gravity

How thick are Saturn’s rings from top to bottom?

a) a few hundred kilometers
b) a few kilometers
c) a few million kilometers
d) a few tens of meters
e) a few tens of thousands of kilometers

d) a few tens of meters

Solar energy leaves the core of the Sun in the form of

a) neutrinos
b) rising hot gas
c) electrons
d) sound waves
e) electromagnetic radiation

e) electromagnetic radiation

What do we mean when we say that the Sun is in gravitational equilibrium?

a) there is a balance within the Sun between the outward push of pressure and the inward pull of gravity
b) the Sun always has the same amount of mass, creating the same gravitational force
c) this is another way of stating that the Sun generates energy by nuclear fusion
d) the Sun maintains a steady temperature
e) the hydrogen gas in the Sun is balanced so that it never rises upward or falls downward

a) there is a balance within the Sun between the outward push of pressure and the inward pull of gravity

We now know of many jupiter-size planets around other stars. Suppose that future observations show that one of these planets has two orbiting moons. What additional information, if any, would we need to decide whether these moons experience tidal heating?

a) we need to know whether either moon is volcanically active
b) we need to know whether the planet also has a third moon
c) no other information is needed: with two moons, there is no possibility of any tidal heating
d) we need to know their orbital periods
e) no other information is needed: with two moons, there is sure to be tidal heating

d) we need to know their orbital periods

Why isn’t there a planet where the asteroid belt is located?

a) the temperature in this portion of the solar nebula was just right to prevent rock from sticking together
b) there was too much rocky material to form a terrestrial planet, but not enough gaseous material to form a jovian planet
c) a planet once formed here, but it was broken apart by a catastrophic collision
d) gravitational tugs from Jupiter prevented material from collecting together to form a planet
e) there was not enough material in this part of the solar nebula to form a planet

d) gravitational tugs from Jupiter prevented material from collecting together to form a planet

Suppose you put two protons near each other. Because of the electromagnetic force, the two protons will

a) attract each other
b) repel each other
c) collide
d) remain stationary
e) join together to form a nucleus

b) repel each other

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