According to modern science, approximately how old is the Sun? a) 400 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. |
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 |
The source of energy that keeps the Sun shining today is _________. a) nuclear fission |
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 |
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 |
The overall result of the proton-proton chain is that __________. a) 4 H becomes 1 He + energy |
a) 4 H becomes 1 He + energy |
To estimate the central temperature of the Sun, scientists _________. a) use computer models to predict interior conditions |
a) use computer models to predict interior conditions |
Solar energy leaves the core of the Sun in the form of a) photons. |
a) photons. |
At the center of the Sun, fusion converts hydrogen into a) plasma. |
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 |
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 |
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 |
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 |
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. |
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. |
Why is Io more volcanically active than our moon? a) Io is much larger. |
c) Io has a different internal heat source. |
Saturn’s many moons affect its rings through a) tidal forces. |
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 |
c) 4:3 |
Which medium-size moon is in a 2:1 resonance with Enceladus? a) Tethys |
c) Dione |
Saturn’s rings are composed of __________. a) gas from the early solar system |
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 |
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. |
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 |
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 |
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. |
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 |
e) tidal heating |
The four Galilean moons around Jupiter are a) very similar to asteroids. |
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. |
The asteroid belt lies between the orbits of a) Earth and Mars. |
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 |
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 |
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 |
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. |
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 |
d) 1 million km |
Where are the Trojan asteroids located? a) in the center of the asteroid belt |
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. |
If we know the size of an asteroid, we can determine its density by a) looking for brightness variations as it rotates. |
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 |
When do comets generally begin to form a tail? a) inside Mercury’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 |
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 |
c) near the jovian planets |
What is the typical size of comets that enter the inner solar system? a) 1 km |
b) 10 km |
The total amount of power (in watts, for example) that a star radiates into space is called its _________. a) luminosity |
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. |
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 |
If star A is closer to us than star B, then Star A’s parallax angle is _________. a) larger 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 |
a) a main-sequence A star |
From hottest to coolest, the order of the spectral types of stars is _________. a) OBAGFKM |
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. |
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 |
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 |
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 |
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. |
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. |
c) They generate energy through hydrogen fusion in their core. |
Which of these layers of the Sun is coolest? a) photosphere |
a) photosphere |
Which of these layers of the Sun is coolest? a) core |
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 |
Corona Chromosphere Photosphere Convection Zone Radiation Zone Core |
Rank the layers of the Sun based on their density, from highest to lowest. Photosphere |
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 Radiation Zone Convection Zone Photosphere |
Rank the following layers of the Sun based on the pressure within them, from highest to lowest. Photosphere |
Core Radiation Zone Convection Zone Photosphere |
In which of the following layer(s) of the Sun does nuclear fusion occur? Photosphere |
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 |
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 |
Which of these groups of particles has the greatest mass? a) a helium nucleus with two protons and two neutrons |
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. |
Which of the following changes would cause the fusion rate in the Sun’s core to increase? a) An increase in the core temperature |
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. |
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. |
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. |
Why do sunspots appear darker than their surroundings? a) They are cooler than their surroundings. |
a) They are cooler than their surroundings. |
What is the most common kind of element in the solar wind? a) hydrogen |
a) hydrogen |
Which of these things poses the greatest hazard to communications satellites? a) photons 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 |
c) green |
How much mass does the Sun lose through nuclear fusion per second? a) 600 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. |
c) repel each other. |
Which is the strongest of the fundamental forces in the universe? a) gravitational force |
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. |
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. |
c) a million years ago. |
What processes are involved in the sunspot cycle? a) the winding of magnetic field lines due to differential rotation |
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. |
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. |
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 |
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 |
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 |
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. |
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. |
The more distant a star, the __________. a) faster its parallax occurs |
d) smaller its parallax angle |
Approximately what is the parallax angle of a star that is 20 light-years away? a) 0.0072 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 |
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 |
How does the Sun generate energy today? a) gravitational contraction |
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 |
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 |
c) inside of Jupiter’s orbit |
The overall fusion reaction by which the Sun currently produces energy is a) 4H => 4He + 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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
d) a few tens of meters |
Solar energy leaves the core of the Sun in the form of a) neutrinos |
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 |
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 |
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 |
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 |
… |
… |
Astronomy Exam 3
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