Part 1

1) Rank the five terrestrial worlds in order of size from smallest to largest:
A) Mercury, Venus, Earth, Moon, Mars.
B) Mercury, Moon, Venus, Earth, Mars.
C) Moon, Mercury, Venus, Earth, Mars.
D) Moon, Mercury, Mars, Venus, Earth.
E) Mercury, Moon, Mars, Earth, Venus.

2) Under what circumstances can differentiation occur in a planet?
A) The planet must have a rocky surface.
B) The planet must be made of both metal and rock.
C) The planet must have an atmosphere.
D) The planet must be geologically active, that is, have volcanoes, planetquakes, and erosion from weather.
E) The planet must have a molten interior.

3) The core, mantle, and crust of a planet are defined by differences in their
A) geological activity.
B) temperature.
C) strength.
D) density.

4) The lithosphere of a planet is the layer that consists of
A) material above the crust.
B) material between the crust and the mantle.
C) the rigid rocky material of the crust and uppermost portion of the mantle.
D) the softer rocky material of the mantle.
E) the lava that comes out of volcanoes.

5) What is the most important factor that determines the thickness, and therefore strength, of the lithosphere?
A) pressure
B) composition
C) internal temperature
D) distance of planet from Sun

6) The terrestrial planet cores contain mostly metal because
A) the entire planets are made mostly of metal.
B) metals condensed first in the solar nebula and the rocks then accreted around them.
C) metals sank to the center during a time when the interiors were molten throughout.
D) radioactivity created metals in the core from the decay of uranium.
E) convection carried the metals to the core.

7) Which internal energy source produces heat by converting gravitational potential energy into thermal energy?
A) accretion
B) differentiation
C) radioactivity
D) both A and B
E) all of the above

8) Which of the following best describes convection?
A) It is the process by which rocks sink in water.
B) It is the process in which warm material expands and rises while cool material contracts and falls.
C) It is the process in which warm material gets even warmer and cool material gets even cooler.
D) It is the process in which a liquid separates according to density, such as oil and water separating in a jar.
E) It is the process in which bubbles of gas move upward through a liquid.

9) What are the circumstances under which convection can occur in a substance?
A) when the substance is subjected to a strong magnetic field
B) when dense material is being added to the substance
C) when the substance is strongly shaken or disturbed by a strong wind
D) when the substance is strongly cooled from underneath
E) when the substance is strongly heated from underneath

10) The three principal sources of the internal heat of terrestrial planets are
A) conduction, differentiation, and accretion.
B) accretion, differentiation, and radioactivity.
C) accretion, differentiation, and eruption.
D) convection, differentiation, and eruption.
E) conduction, convection, and eruption.

11) Which of the following worlds have the thinnest lithospheres?
A) Earth and the Moon
B) Venus and the Moon
C) Mercury and Venus
D) Earth and Mars
E) Earth and Venus

12) Which of the terrestrial worlds has the strongest magnetic field?
A) Mars
B) Earth
C) the Moon
D) Venus
E) Mercury

13) Why does Earth have the strongest magnetic field among the terrestrial worlds?
A) It is the only one that has a metallic core.
B) It rotates much faster than any other terrestrial world.
C) It is the only one that has both a partially molten metallic core and reasonably rapid rotation.
D) It is by far the largest terrestrial world.
E) It is the most volcanically active world.

14) Which of the following most likely explains why Venus does not have a strong magnetic field?
A) It does not have a metallic core.
B) Its rotation is too slow.
C) It is too close to the Sun.
D) It is too large.
E) It has too thick an atmosphere.

15) What are the conditions necessary for a terrestrial planet to have a strong magnetic field?
A) a molten metallic core only
B) fast rotation only
C) a rocky mantle only
D) both a molten metallic core and reasonably fast rotation
E) both a metal core and a rocky mantle

16) Which of the following has virtually no effect on the internal structure of a planet?
A) its composition
B) its size
C) its magnetic field
D) its mass

17) Which of the following does not have a major effect in shaping planetary surfaces?
A) impact cratering
B) volcanism
C) tectonics
D) erosion
E) magnetism

18) How large is an impact crater compared to the size of the impactor?
A) the same size
B) 10-20 percent larger
C) 10 times larger
D) 100 times larger
E) 1,000 times larger

19) How deep is an impact crater compared to its width?
A) 1-10%
B) 10-20%
C) 30-40%
D) 50-100%
E) 100-200%

20) When we see a region of a planet that is not as heavily cratered as other regions, we conclude that
A) there is little volcanic activity to create craters.
B) the planet is rotating very slowly and only one side was hit by impactors.
C) the planet formed after the age of bombardment and missed out on getting hit by leftover planetesimals.
D) the surface in the region is older than the surface in more heavily cratered regions.
E) the surface in the region is younger than the surface in more heavily cratered regions.

21) Volcanism is more likely on a planet that
A) is closer to the Sun.
B) is struck often by meteors and solar system debris.
C) has high internal temperatures.
D) doesn't have an atmosphere or oceans.

22) Which of the following describes tectonics?
A) the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface
B) the eruption of molten rock from a planet's interior to its surface
C) the disruption of a planet's surface by internal stresses
D) the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather

23) Which of the following describes erosion?
A) the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface
B) the eruption of molten rock from a planet's interior to its surface
C) the disruption of a planet's surface by internal stresses
D) the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather

24) Which of the following describes volcanism?
A) the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface
B) the eruption of molten rock from a planet's interior to its surface
C) the disruption of a planet's surface by internal stresses
D) the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather

25) Which of the following describes impact cratering?
A) the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface
B) the eruption of molten rock from a planet's interior to its surface
C) The disruption of a planet's surface by internal stresses
D) the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather

26) A planet is most likely to have tectonic activity if it has
A) low surface gravity.
B) high surface gravity.
C) low internal temperature.
D) high internal temperature.
E) a dense atmosphere.

27) How have we been able to construct detailed maps of surface features on Venus?
A) by studying Venus from Earth with powerful telescopes
B) by studying Venus with powerful telescopes on spacecraft that were sent to orbit Venus
C) By making computer models of geological processes on Venus
D) by using radar from spacecraft that were sent to orbit Venus
E) by landing spacecraft on the surface for close-up study

28) Which of the following show evidence of ancient river beds?
A) the Moon
B) Mercury
C) Venus
D) Mars
E) all of the above

29) Why is Mars red?
A) It is made primarily of red clay.
B) Its surface rocks were rusted by oxygen.
C) Its atmosphere scatters blue light more effectively than red light.
D) Its surface is made of ices that absorb blue light.
E) Its surface is made of ices that absorb red light.

30) Where is most of the water on Mars?
A) in its clouds
B) in its polar caps and subsurface ground ice
C) frozen on the peaks of its tall volcanoes
D) in deep underground deposits
E) distributed evenly throughout its atmosphere

31) Spacecraft have landed on all the terrestrial worlds except:
A) Mercury.
B) Venus.
C) Moon.
D) Mars.

32) Which of the following worlds has the most substantial atmosphere?
A) Mercury
B) Venus
C) the Moon
D) Mars
E) Earth

33) Which of the following planets has the least substantial atmosphere?
A) Venus
B) Earth
C) Mars
D) Neptune
E) Mercury

34) Suppose Earth's atmosphere had no greenhouse gases. Then Earth's average surface temperature would be
A) -16°C, which is well below freezing.
B) 0°C, or about the freezing point for water.
C) 10°C or about 5°C cooler than it is now.
D) 15°C, or about the same as it is now.
E) 20°C, or about 5°C warmer than it is now.

35) What are greenhouse gases?
A) gases that absorb visible light
B) gases that absorb ultraviolet light
C) gases that absorb infrared light
D) gases that transmit visible light
E) gases that transmit infrared light

36) Sunsets are red because
A) the Sun emits more red light when it's setting.
B) sunlight must pass through more atmosphere, and this scatters even more light at bluer wavelengths, transmitting mostly red light.
C) sunlight must pass through more atmosphere, and this scatters more light at red wavelengths than bluer wavelengths.
D) the cooler atmosphere in the evening absorbs more blue light.
E) none of the above

37) Why does Mars have more extreme seasons than Earth?
A) because it is farther from the Sun
B) because it has a larger axis tilt
C) because it has a more eccentric orbit
D) Because it has more carbon dioxide in its atmosphere
E) all of the above

38) From where did the oxygen in the earth's atmosphere originate?
A) photosynthesis from plant life and single-celled organisms
B) chemical reactions between gas in the upper atmosphere and the solar wind
C) outgassing from volcanoes
D) atmospheric bombardment
E) oxidation of surface rocks

39) What process has shaped Earth's surface more than any other?
A) impact cratering
B) volcanism
C) plate tectonics
D) wind erosion
E) acid rain

40) What drives the motion of the continental plates on Earth?
A) convection cells in the mantle
B) rotation of the liquid core
C) lava flows in trenches along the sea floor
D) Earth's magnetic field
E) tidal forces

41) Of the four gases CO2, H2O, N2, and O2, which are greenhouse gases?
A) only CO2
B) CO2 and H2O
C) CO2 and N2
D) all except O2
E) all four

Part 2

1) If Jupiter were scaled to the size of a basketball, Earth would be the closest to the size of
A) a pinhead.
B) a marble.
C) a baseball.
D) a grapefruit.
E) a basketball.

2) How many more times is the atmospheric pressure in Jupiter's core greater than the atmospheric pressure at Earth's surface?
A) 10 thousand
B) 100 thousand
C) 1 million
D) 10 million
E) 100 million

3) How do astronomers think Jupiter generates its internal heat?
A) radioactive decay
B) internal friction due to its high rotation rate
C) chemical processes
D) nuclear fusion in the core
E) by contracting, changing gravitational potential energy into thermal energy

4) Why is Jupiter denser than Saturn?
A) It is made of a different composition than Saturn, including a higher proportion of hydrogen compounds and rocks.
B) The extra mass of Jupiter compresses its interior to a greater extent than that of Saturn.
C) Its core is much larger than Saturn's.
D) It has a greater proportion of helium to hydrogen compared to Saturn.
E) Scientists do not know why this is so.

5) Why is Neptune denser than Saturn?
A) It has a different composition than Saturn, including a higher proportion of hydrogen compounds and rocks.
B) It has a greater proportion of hydrogen than Saturn.
C) The extra mass of Neptune compresses its interior to a greater extent than that of Saturn.
D) Its hydrogen is molecular, whereas Saturn's hydrogen is atomic.
E) It is not denser than Saturn.

6) How do the jovian planet interiors differ?
A) All have cores of about the same mass, but differ in the amount of surrounding hydrogen and helium.
B) The core mass decreases with the mass of the planet.
C) The composition changes from mostly ammonia in Jupiter and Saturn to mostly methane in Uranus and Neptune.
D) The composition changes from mostly hydrogen in Jupiter and Saturn to mostly helium in Uranus and Neptune.
E) All have about the same amount of hydrogen and helium but the proportion of rocks is greater in those planets closer to the Sun.

7) Why does Jupiter have several distinct cloud layers?
A) Different layers represent clouds made of gases that condense at different temperatures.
B) Different layers represent the various regions where the temperature is cool enough for liquid water to condense.
C) Different gases are present at different altitudes in Jupiter's atmosphere.
D) Winds prevent clouds from forming at some altitudes, so we see clouds only at the other altitudes.
E) Clouds form randomly, so on average there are always several layers.

8) What is the most important reason why an icy moon is more likely to be geologically active than a rocky moon of the same size?
A) Ice has a lower melting point than rock.
B) Ice is less rigid than rock.
C) Ice contains more radioactive elements than rock.
D) Ice is affected by tidal forces to a greater extent than rock.
E) Ice is less dense than rock.

9) What mechanism is most responsible for generating the internal heat of Io that drives its volcanic activity?
A) accretion
B) radioactive decay
C) differentiation
D) tidal heating
E) bombardment

10) How thick are Saturn's rings from top to bottom?
A) a few million kilometers
B) a few tens of thousands of kilometers
C) a few hundred kilometers
D) a few kilometers
E) a few tens of meters

11) Which of the following best describes the composition of the particles forming Saturn's rings?
A) Water ice
B) Metallic grains
C) Methane ice
D) Volcanic rock
E) Hydrogen and helium

12) Why are Saturn's rings so thin?
A) Saturn's gravity prevents particles from migrating upwards out of the rings.
B) The "gap" moons shepherd the particles and maintain its thin profile.
C) Any particle in the ring with an orbital tilt would collide with other ring particles, flattening its orbit.
D) Solar radiation pressure keeps particles pressed into the rings.
E) The current thinness is a short-lived phenomenon that is special to this time.

13) What is the Cassini division of Saturn's rings?
A) a dark ring, visible from Earth, composed of dark, dusty particles
B) a large gap, visible from Earth, produced by an orbital resonance with the moon Mimas
C) the imaginary circle marking the halfway point of Saturn's rings
D) the widest ring of Saturn, located between two large ring gaps
E) the most opaque ring of Saturn, made of highly reflective ice particles

14) Which of the jovian planets have rings?
A) Jupiter
B) Saturn
C) Uranus
D) Neptune
E) all of the above

15) How does the strength of Jupiter's magnetic field compare to that of Earth's magnetic field?
A) Jupiter's magnetic field is about 20,000 times as strong as Earth's.
B) Jupiter's magnetic field strength is about the same as Earth's.
C) Jupiter's magnetic field is about twice as strong as Earth's.
D) Jupiter's magnetic field is much weaker than Earth's.

16) Which of the following statements about the moons of the jovian planets is not true?
A) Most of the moons are large enough to be spherical in shape, but a few have the more potato-like shapes of asteroids.
B) Some of the moons are big enough that we'd call them planets (or dwarf planets) if they orbited the Sun.
C) One of the moons has a thick atmosphere.
D) Many of the moons are made largely of ices.

17) Suppose you could float in space just a few meters above Saturn's rings. What would you see as you looked down on the rings?
A) countless icy particles, ranging in size from dust grains to large boulders
B) a solid, shiny surface, looking much like a piece of a DVD but a lot bigger
C) dozens of large "moonlets" made of metal and rock, each a few kilometers across
D) Nothingup close, the rings would be so completely invisible that you'd have no way to know they are there. They can be seen only from a distance.

18) Jupiter and the other jovian planets are sometimes called "gas giants." In what sense is this term misleading?
A) They actually contain relatively little material in a gaseous state.
B) The materials they are made of are not the kinds of thing we usually think of as gases.
C) They are not in any sense "giants."
D) Actually, it's a great description, because these worlds are big and gaseous throughout.

19) What would happen to Jupiter if we could somehow double its mass?
A) Its density would increase but its diameter would barely change.
B) Its density would decrease and its diameter would double.
C) Its density would stay about the same and its volume would double.
D) It would become a star, with nuclear fusion in its core.

20) According to our theory of solar system formation, why did Uranus and Neptune end up to be much less massive than Jupiter and Saturn?
A) Particles in the solar nebula were more spread out at greater distances, so that accretion took longer and there was less time to pull in gas before the solar wind cleared the nebula.
B) Ices were able to condense at the distance of Jupiter and Saturn, but only rock and metal could condense at the distances of Uranus and Neptune.
C) The colder gas in the outer regions of the solar nebula had less gravity and therefore could not gather up into such large balls as it could closer in.
D) The size differences are thought to be a random coincidence.

Part 3

1) Which of the following statements about comets and asteroids is true?
A) Only asteroids collide with Earth.
B) Comets are balls of ice and dust.
C) Most of the trillions of comets in our solar system have tails.
D) All asteroids lie in the asteroid belt between Mars and Jupiter.
E) There are about 1 million known asteroids in the solar system.

2) What do asteroids and comets have in common?
A) Most are unchanged since their formation in the solar nebula.
B) They have similar densities.
C) They have similar orbital radii.
D) They have a similar range of orbital inclinations.
E) They have nothing in common with each other.

3) How do asteroids differ from comets?
A) Asteroids are made of rocky material. Comets are made of icy material.
B) Asteroids are made of icy material. Comets are made of rocky material.
C) Asteroids and comets are both made of rocky and icy material, but asteroids are larger in size than comets.
D) Asteroids and comets are both made of rocky and icy material, but asteroids are smaller in size than comets.

4) Why do asteroids and comets differ in composition?
A) Asteroids formed inside the frost line, while comets formed outside.
B) Asteroids and comets formed at different times.
C) Comets formed from the jovian nebula, while asteroids did not.
D) Comets are much larger than asteroids.
E) Asteroids are much larger than comets.

5) Why aren't small asteroids spherical in shape?
A) The strength of gravity on small asteroids is less than the strength of the rock.
B) Small asteroids have odd shapes because they were all chipped off larger objects.
C) Large asteroids were once molten and therefore became spherical, but small asteroids were never molten.
D) Large asteroids became spherical because many small collisions chipped off pieces until only a sphere was left; this did not occur with small asteroids.

6) What is a meteorite?
A) a streak of light caused by a star moving across the sky
B) a streak of light caused by a small particle from space burning up in Earth's atmosphere
C) a fragment of an asteroid from the solar system that has fallen to Earth's surface
D) a small moon that orbits one of the giant planets
E) a comet that burns up in Earth's atmosphere

7) A typical shooting star in a meteor shower is caused by a ________ entering Earth's atmosphere.
A) boulder-size particle from an asteroid
B) boulder-size particle from a comet
C) pea-size particle from an asteroid
D) pea-size particle from a comet
E) microscopic particle of interstellar dust

8) What characteristic distinguishes a meteorite from a terrestrial rock?
A) A meteorite is usually covered with a dark crust from burning in Earth's atmosphere.
B) A meteorite usually has a high metal content.
C) Meteorites have different isotope ratios of particular elements when compared to terrestrial rocks.
D) Meteorites contain rare elements, such as iridium, that terrestrial rocks do not.
E) All of the above are true.

9) Primitive meteorites can be distinguished from other meteorites and terrestrial rocks because they
A) contain a noticeable fraction of pure metallic flakes.
B) resemble the composition of Earth's core.
C) contain a lot of iron and were used by humans to make iron tools.
D) resemble the composition of Earth's mantle.
E) resemble the composition of rocks from lava flows that occurred on asteroids very shortly after the formation of the solar system.

10) Meteorites can come from
A) the cores of asteroids.
B) the crusts and mantles of asteroids
C) the Moon.
D) Mars
E) all of the above

11) What part of a comet always points most directly away from the Sun?
A) the nucleus
B) the coma
C) the jets of gas
D) the plasma tail
E) the dust tail

12) Why does the plasma tail of a comet always point away from the Sun?
A) The solar wind blows the plasma ions directly away from the Sun.
B) Radiation pressure from the Sun's light pushes the ions away.
C) The conservation of the angular momentum of the tail keeps it always pointing away from the Sun.
D) Gases from the comet, heated by the Sun, push the tail away from the Sun.
E) It is allergic to sunlight.

13) What is the typical size of a comet's nucleus?
A) 1 meter
B) 10 km
C) 100 km
D) 1000 km
E) Sizes are unknown because the nucleus is obscured by the coma.

14) Rather than being a planet, Pluto is really just a large member of
A) the asteroid belt.
B) the Kuiper belt.
C) the Oort cloud.
D) the moon system around Neptune.
E) an extrasolar planetary system.

15) Why was the Shoemaker-Levy 9 impact so important to astronomers?
A) It dredged up material that gave us our first direct look at Jupiter's interior composition.
B) It wiped out the dinosaurs.
C) It was the first direct proof that impacts really occur.
D) It confirmed our theory of solar system formation.
E) It was the first event in modern history that was brighter than the full moon in the sky.

16) Which of the following statements about comets best describes the light we can observe?
A) A comet emits visible light and infrared light
B) A comet emits no light, but reflects visible light.
C) A comet emits infrared light and reflects visible light.
D) A comet emits visible light and reflects infrared light.

17) During the time that a comet passes through the inner solar system, the comet can appear quite bright because
A) increasing friction causes the comet's nucleus to glow.
B) heat from the Sun 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.

18) The total number of comets orbiting the Sun is estimated to be about ________.
A) 1 trillion
B) 1,000
C) 100,000
D) 1 million

Part 4

1) Which of the following is the phase of matter in the Sun?
A) gas
B) plasma
C) liquid
D) solid
E) a mixture of all of the above

2) Which is closest to the temperature of the Sun's core?
A) 10,000 K
B) 100,000 K
C) 1 million K
D) 10 million K
E) 100 million K

3) The core of the Sun is
A) at the same temperature and density as its surface.
B) at the same temperature but much denser than its surface.
C) much hotter and much denser than its surface.
D) constantly rising to the surface through convection.
E) composed of iron.

4) Based on its surface temperature of 6,000 K, most photons that leave the Sun's surface lie in which region of the electromagnetic spectrum?
A) Microwave
B) Infrared
C) Visible
D) Ultraviolet
E) X-ray

5) Sunspots are cooler than the surrounding gas in the photosphere because
A) they are regions where convection carries cooler material downward.
B) strong magnetic fields slow convection and prevent hot plasma from entering the region.
C) magnetic fields trap ionized gases that absorb light.
D) there is less fusion occurring there.
E) magnetic fields lift material from the sunspot and quickly cool the material.

6) By what process does the Sun generate energy?
A) nuclear fission
B) nuclear fusion
C) chemical reactions
D) gravitational contraction
E) gradual expansion

7) Hydrogen fusion in the Sun requires a temperature (in Kelvin) of
A) thousands of degrees.
B) millions of degrees.
C) billions of degrees.
D) trillions of degrees.
E) any temperature, as long as gravity is strong enough.

8) At the center of the Sun, nuclear fusion converts hydrogen into
A) hydrogen compounds such as methane.
B) molecular hydrogen.
C) radiation and elements such as carbon and nitrogen.
D) radioactive elements such as uranium and plutonium.
E) helium, gamma rays, and neutrinos.

9) How much mass does the Sun lose through nuclear fusion per second?
A) 4 tons
B) 4 million tons
C) 600 tons
D) 600 million tons
E) Nothing: mass-energy is conserved.

10) Suppose you try to bring two protons close together. Because of the electromagnetic force, the two protons will
A) collide.
B) remain stationary.
C) attract one another.
D) repel one another.
E) join together to form a deuterium nucleus.

11) Studies of solar vibrations have revealed that
A) the Sun vibrates only on the surface.
B) they are caused by processes similar to those that create earthquakes.
C) the Sun generates energy by nuclear fusion.
D) our mathematical models of the solar interior are fairly accurate.
E) neutrinos from the solar core reach the solar surface easily.

12) Imagine that you are trying to stop neutrinos with a lead shield. How thick would you need to make this shield to ensure that it can stop a neutrino?
A) About one meter.
B) About 700,000 kilometers (the radius of the Sun).
C) About 150 million kilometers (the size of an astronomical unit).
D) About one light year.
E) About 14 billion light years (the size of the observable universe).

13) The light radiated from the Sun's surface reaches Earth in about 8 minutes. However, the energy of this light was released by fusion in the Sun's core about
A) 8 minutes ago.
B) 11 years ago.
C) several hundred years ago.
D) several thousand years ago.
E) several hundred thousand years ago.

14) When the temperature of the Sun's core goes down, what happens next?
A) Fusion reactions speed up, the core shrinks and cools.
B) Fusion reactions speed up, core expands and cools.
C) Fusion reactions slow down, core shrinks and heats.
D) Fusion reactions slow down, the core expands and heats.

15) Order the interior layers of the Sun from the hottest to the coldest.
A) Photosphere, convection zone, core, radiation zone
B) Core, radiation zone, convection zone, photosphere
C) Radiation zone, core, convection zone, photosphere
D) Photosphere, convection zone, radiation zone, core

16) Why isn't the Sun shrinking or expanding?
A) Because the Sun is spinning so fast, the centrifugal forces keep the surface of the Sun supported against collapse
B) Because the Sun has lived for billions of years
C) Because the Sun is solid
D) Because gas pressure balances gravity in the Sun

17) What would happen in the Sun if the temperature of the core decreased?
A) The fusion rate decreases, then the core shrinks and heats.
B) The fusion rate decreases, then the core expands and heats.
C) The fusion rate increases, then the core expands and cools.
D) The fusion rate increases, then the core shrinks and heats.

18) Which of the following correctly describes how the process of gravitational contraction can make a star hot?
A) When a star contracts in size, gravitational potential energy is converted to thermal energy.
B) Gravitational contraction involves nuclear fusion, which generates a lot of heat.
C) Heat is generated when gravity contracts because gravity is an inverse square law force.
D) Gravitational contraction involves the generation of heat by chemical reactions, much like the burning of coal.

19) What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?
A) The strong force and the weak force
B) Gravitational force and outward pressure
C) Gravitational force and surface tension
D) The strong force and the electromagnetic force

20) When we say that the Sun is a ball of plasma, we mean that ________.
A) the Sun is made of material that acts like a liquid acts on Earth
B) the Sun is made of atoms and molecules
C) the Sun consists of gas in which many or most of the atoms are ionized (missing electrons)
D) the Sun is roughly the same color as blood

21) What are the appropriate units for the Sun's luminosity?
A) Watts
B) Joules
C) Newtons
D) Kilograms

22) The Sun's surface, as we see it with our eyes, is called the ________.
A) photosphere
B) chromosphere
C) corona
D) core

23) What is the solar wind?
A) A stream of charged particles flowing outward from the surface of the Sun
B) The uppermost layer of the Sun, lying just above the corona
C) The strong wind that blows sunspots around on the surface of the Sun
D) The wind that causes huge arcs of gas to rise above the Sun's surface

24) Why are neutrinos so difficult to detect?
A) They have a tendency to pass through just about any material without any interactions.
B) They are extremely rare.
C) They have no mass.
D) No one knows: this is the essence of the "solar neutrino problem."

25) What do sunspots, solar prominences, and solar flares all have in common?
A) They are all strongly influenced by magnetic fields on the Sun.
B) They all have about the same temperature.
C) They are all shaped by the solar wind.
D) They all occur only in the Sun's photosphere.

26) How is the sunspot cycle directly relevant to us here on Earth?
A) Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment.
B) The sunspot cycle strongly influences Earth's weather.
C) The Sun's magnetic field, which plays a major role in the sunspot cycle, affects compass needles that we use on Earth.
D) The brightening and darkening of the Sun that occurs during the sunspot cycle affects plant photosynthesis here on Earth.
E) The sunspot cycle is the cause of global warming.

27) Which of the following is the best answer to the question, "Why does the Sun shine?"
A) As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.
B) As the Sun was forming, nuclear fusion reactions in the shrinking clouds of gas slowly became stronger and stronger, until the Sun reached its current luminosity.
C) The Sun initially began making energy through chemical reactions. These heated the interior enough to allow gravitational contraction and nuclear fusion to occur.
D) The Sun initially began generating energy through nuclear fusion as it formed, but today it generates energy primarily through the sunspot cycle.

28) How can we measure the strength of magnetic fields on the Sun?
A) By looking for the splitting of spectral lines in the Sun's spectrum
B) By observing the sizes of sunspots: Bigger sunspots mean a stronger field
C) By observing auroras here on Earth
D) Only by using sophisticated computer models because there are no observational ways of measuring magnetic field strength

29) Satellites in low-Earth orbits are more likely to crash to Earth when the sunspot cycle is near solar maximum because ________.
A) it is too dangerous to send the Space Shuttle to service satellites during solar maximum
B) Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits
C) of increased magnetic interference
D) they are more likely to have their electronics "fried" by a solar flare during solar maximum

30) Which of the following choices is not a way by which we can study the inside of the Sun?
A) We can send a space probe into the Sun's photosphere.
B) We can probe the interior of the Sun by studying the vibrations in its photosphere.
C) We can make a computer model of the Sun's interior that allow us to predict the observable properties of the Sun.
D) We can study solar neutrinos.

Part 1 1) Rank the five terrestrial worlds in order of size from...