Astronomy midterm 3

Which of the following correctly describes patterns of motion in the solar system?

Check all that apply.
1) inner planets orbit the sun in the opposite direction from the outer planets
2) planets closer to the sun move around their orbits at higher speed than planets farther from the sun.
3) The outer planets are so large that they nearly collide with each other on each orbit.
4)all the planets (not counting Pluto) orbit the sun in nearly the same plane.
5) all the planets (not counting Pluto) have nearly circular orbits.
6) The inner planets all rotate in the same direction (west to east) as earth.

2, 4, 5
The materials that made up the solar nebula can be categorized into these four general types. Rank these materials from left to right based on the temperature at which each would condense into a solid, from highest to lowest. Note: for a substance that does not condense at all, rank it as very low temperature.

Hydrogen and helium gas
Hydrogen compounds
Metal
Rock

Highest to lowest temperature:
Metals
Rock
Hydrogen compounds
Hydrogen and helium gas
What substances existed as solid flakes within the inner 0.3 AU of the solar system before planets began to form?

A) none
B) only rocks and metals
C) only hydrogen compounds
D) only hydrogen and helium gases

A) none
The Jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetesimals made of:

A) only rocks and metals
B) only ices
C) rocks, metals, and ices
D) rocks, metals, ices, and hydrogen and helium gases

C) rocks, metals, and ices
In what way is Venus most similar to earth?
A) both planets have warm days and cool nights.
B) both planets have very similar atmospheres.
C) both planets have similar surface geology.
D) both planets are nearly the same size.
D) both planets are nearly the same size.
Imagine that an alien spaceship crashed onto earth. Which statement would most likely be true?

A) The aliens home world is another planet in our own solar system
B) it would crash in the ocean.
C) all the evidence of the crash would be quickly whisked off by the US military to area 51 in Nevada
D) The crash would create a noticeable crater

B) it would crash in the ocean
According to present understanding, which of the following statements about the solar wind is not true?

A) it is even stronger today than it was when the sun was young.
B) it helped in the transfer of angular momentum from the young sun to particles that blew into interstellar space, which explains why the sun rotates so slowly today.
C) it swept vast amounts of gas from the solar nebula into interstellar space.
D) it consists of charged particles blown off the surface of the sun.

A) it is even stronger today than it was when the sun was young.
According to our present theory of solar system formation, how did earth end up with enough water to make oceans?

A) Earth formed at a distance from the sun at which liquid water happened to be plentiful in the solar nebula
B) The water was brought to the forming earth by planetesimals that accreted beyond the orbit of mars.
C) The water was brought to the forming earth by planetesimals that accreted near earths orbit.
D) The water was formed by chemical reactions among the minerals in the earths score.

B) The water was brought to the forming earth by planetesimals that accreted beyond the orbits of Mars
According to our present theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system?

A) because only metal and rock could condense in the inner solar system, while ice also condensed in the outer solar system
B) because gas in the outer solar system contained a larger portion of rock, metal, and hydrogen compounds than the gas in the inner solar system
C) because only the outer planets captured hydrogen and helium gas from the solar nebula
D) because the suns gravity was stronger in the outer solar system, allowing more solid material to collect

A) because only metal and rock could condense in the inner solar system, while ice also condensed in the outer solar system
According to our basic scenario of solar system formation, why do the Jovian planets have numerous large moons?

A) because of their strong gravity, the Jovian planets were able to capture numerous asteroids that happened to be passing nearby, and these became the major moons of the Jovian planets.
B) The many moons of the Jovian planets remains one of the unexplained mysteries of the formation of our solar system.
C) as the groaning Jovian planets captured gas from the solar nebula, the gas for swirling disks around them, and moons formed from condensation accretion within these disks
D) The large moons of the Jovian planets originally formed in the inner solar system, and these moons then migrated out to join up with the Jovian planets

C) as the groaning Jovian planets captured gas from the solar nebula, the gas for swirling disks around them, and moons formed from condensation accretion within these disks
Which of the following is not evidence supporting the idea that our moon formed as a result of a giant impact?

A) The Pacific ocean appears to be a large crater-probably the one made by the giant impact.
B) The moon has a much smaller proportion of easily vaporized materials than earth
C) Computer simulations show that the Moon could really have formed in this way.
D) The moons average density suggest it is made of rock much more like that of earths outer layers than that of the earth as a whole.

A) The Pacific ocean appears to be a large crater-probably the one made by the giant impact.
The Cassini mission to Saturn consists of _______________.

A) A large spacecraft that flew by Saturn on its way to other planets.
B) A spacecraft that orbits Saturn and a sample return mission that landed on Titan, scooped up a surface sample, and will return it to earth
C) an orbiter that orbits Saturn and probe that descended into Saturn’s atmosphere
D) an orbiter that orbits Saturn and a probe that descended to the surface of titan

D) an orbiter that orbits Saturn and a probe that descended to the surface of titan
Which of the following types of material can condense into what we call ice at low temperatures?

A) hydrogen compounds
B) metal
C) hydrogen and helium
D) rock

A) Hydrogen compounds
What do we mean by the frost line when we discuss the formation of planets in the solar nebula?

A) It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.
B) It is the altitude in a planet’s atmosphere at which snow can form.
C) It marks the special distance from the Sun at which hydrogen compounds become abundant; closer to the Sun, there are no hydrogen compounds.
D) It is another way of stating the temperature at which water freezes into ice.

A) It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.
What do we mean by accretion in the context of planet formation?

A) the growth of planetesimals from smaller solid particles that collided and stuck together
B) the growth of the Sun as the density of gas increased in the center of the solar nebula
C) the solidification of ices, rocks, and metal from the gas of the solar nebular
D) the formation of moons around planets

A) the growth of planetesimals from smaller solid particles that collided and stuck together
What is the giant impact hypothesis for the origin of the Moon?

A) The Moon formed when two gigantic asteroids collided with one another.
B) The Moon originally was about the same size as Earth, but a giant impact blasted most of it away so that it ended up much smaller than Earth.
C) The Moon formed from material blasted out of the Earth’s mantle and crust by the impact of a Mars-size object.
D) The Moon formed just like the Earth, from accretion in the solar nebula.

C) The Moon formed from material blasted out of the Earth’s mantle and crust by the impact of a Mars-size object.
Which planet has the highest average surface temperature, and why?

A) Venus, because of its dense carbon dioxide atmosphere
B) Mars, because of its red color
C) Mercury, because it is closest to the Sun
D) Mercury, because of its dense carbon dioxide atmosphere
E) Jupiter, because it is so big

A) Venus, because of its dense carbon dioxide atmosphere
Which planet, other than Earth, has visible water ice on it?

A) the Moon
B) Venus
C) Mars
D) Mercury
E) Jupiter

C) Mars
Where are most of the known asteroids found?

A) in the Kuiper belt
B) between the orbits of the terrestrial planets
C) in the Oort cloud
D) between the orbits of the jovian planets
E) between the orbits of Mars and Jupiter

E) between the orbits of Mars and Jupiter
Which of the following is furthest from the Sun?

A) an asteroid in the asteroid belt
B) Pluto
C) Neptune
D) a comet in the Oort cloud
E) a comet in the Kuiper belt

D) a comet in the Oort cloud
Astronomers now classify Pluto as really just a large member of

A) the asteroid belt.
B) the Oort cloud.
C) the moon system around Neptune.
D) the Kuiper belt.
E) an extrasolar planetary system.

D) the Kuiper belt.
According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane?

A) The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk.
B) The Sun formed first, and as it grew in size it spread into a disk, rather like the way a ball of dough can be flattened into a pizza by spinning it.
C) The original solar nebula happened to be disk-shaped by chance.
D) Luck explains it, as we would expect that most other solar systems would not have all their planets orbiting in such a pattern.
E) Any planets that once orbited in the opposite direction or a different plane were ejected from the solar system.

A) The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk.
Which of the following lists the ingredients of the solar nebula from highest to lowest percentage of mass of the nebula?

A) hydrogen compounds (H2O, CH4, NH3), rocks, metals, light gases (H, He)
B) hydrogen compounds (H2O, CH4, NH3), light gases (H, He), metals, rocks
C) light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
D) light gases (H, He), hydrogen compounds (H2O, CH4, NH3), metals, rocks
E) hydrogen compounds (H2O, CH4, NH3), light gases (H, He), rocks, metals

C) light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
If the freezing point of ices of all types were at a much lower temperature, what change would that imply for the formation of our solar system?

A) There would be no change in where gas giants could form, because the freezing point of ices did not affect the formation of gas giants.
B) The gas giants would have to form at a larger distance.
C) The gas giants could have formed at a closer distance.

B) The gas giants would have to form at a larger distance.
Which of the following statements best explains why the planets orbit in nearly a single plane and in the same direction around the Sun?

A) The Sun rotates in the same direction, and spun out the planets as it formed.
B) The planets formed from a disk of rotating gas.
C) The planets all rotate in same direction as they orbit.
D) It’s a mysterious coincidence: the planets form randomly, so it’s a puzzle how they orbit that way.

B) The planets formed from a disk of rotating gas.
How do we know the mass of Neptune?

A) the period and size of Neptune’s orbit around the Sun
B) the orbital speed of Neptune moving around the Sun
C) the size and density of Neptune
D) the periods and sizes of the orbits of the moons around Neptune
E) the distance of Neptune from the Earth and its rotation period

D) the periods and sizes of the orbits of the moons around Neptune
Which of the following lists the ingredients of the solar nebula from highest to lowest percentage of mass of the nebula?

A) hydrogen compounds (H2O, CH4, NH3), rocks, metals, light gases (H, He)
B) hydrogen compounds (H2O, CH4, NH3), light gases (H, He), metals, rocks
C) light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
D) light gases (H, He), hydrogen compounds (H2O, CH4, NH3), metals, rocks
E) hydrogen compounds (H2O, CH4, NH3), light gases (H, He), rocks, metals

Following are the different layers of the Sun’s atmosphere. Rank them based on the order in which a probe would encounter them when traveling from Earth to the Sun’s surface, from first encountered to last.

Photosphere
corona
chromosphere

corona
chromosphere
photosphere
Rank the layers of the Sun’s atmosphere based on their density, from highest to lowest.

chromosphere
Photosphere
corona

photosphere
chromosphere
corona
Which of the following must occur for a star’s core to reach equilibrium after an initial change in fusion rate?
Check all that apply.

1) If the fusion rate initially decreases, then the core expands.
2) If the fusion rate initially increases, then the core expands.
3) If the fusion rate initially decreases, then the core contracts.
4) If the fusion rate initially increases, then the core contracts.

2) If the fusion rate initially increases, then the core expands.
3) If the fusion rate initially decreases, then the core contracts.
Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once.

1) Nuclear fusion of hydrogen into helium occurs in the ____________.
2) Energy moves through the Sun’s __________ by means of the rising of hot gas and falling of cooler gas.
3) Nearly all the visible light we see from the Sun is emitted from the ____________.
4) Most of the Sun’s ultraviolet light is emitted from the narrow layer called the _____________ where temperature increases with altitude.
5) We can see the Sun’s _____________ most easily during total solar eclipses.
6) The __________ is the layer of the Sun between its core and convection zone.

Photosphere
convection zone
corona
core
radiation zone
chromosphere

1) core
2) convection zone
3) photosphere
4) chromosphere
5) corona
6) radiation zone
A solar model is used to calculate the expected temperature and density at all depths within the Sun. These results are then used to calculate the expected fusion rate within the Sun. We have confidence that the model is correct because it agrees with the observed characteristics of the Sun. Which of the following observations can be used to check that we really do know the Sun’s internal fusion rate?
Select all that apply.

1) Observations of neutrinos coming from the Sun
2) Observations of the total X-ray emission from the Sun’s corona
3) Measurements of the Sun’s total energy output into space
4) Measurements of the varying number of sunspots on the Sun over time
5) Measurement of the Sun’s mass

1 & 3
In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot due to gravitational contraction. What was the major drawback to this idea?

A) It predicted that the Sun would shrink noticeably as we watched it, but the Sun appears to be stable in size.
B) It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.
C) It is physically impossible to generate heat simply by making a star shrink in size.
D) It predicted that Earth would also shrink in size with time, which would make it impossible to have stable geology on our planet.

B) It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.
Which of the following best describes why the Sun emits most of its energy in the form of visible light?

A) The visible light comes from energy level transitions as electrons in the Sun’s hydrogen atoms jump between level 1 and level 2.
B) Nuclear fusion in the Sun’s core produces visible light photons.
C) The Sun’s gas is on fire like flames from wood or coal, and these flames emit visible light.
D) Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun’s surface temperature is just right for emitting mostly visible light.

D) Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun’s surface temperature is just right for emitting mostly visible light.
If the Sun’s core suddenly shrank a little bit, what would happen in the Sun?

A) The density of the core would decrease, causing the core to cool off and expand.
B) The core would cool off and continue to shrink as its density increased.
C) The core would heat up, fusion rates would increase, the core would re-expand.
D) The core would heat up, causing it to radiate so much energy that it would shrink even more.

C) The core would heat up, fusion rates would increase, the core would re-expand.
Why does the Sun emit neutrinos?

A) The Sun was born with a supply of neutrinos that it gradually emits into space.
B) Solar flares create neutrinos with magnetic fields.
C) Convection releases neutrinos, which random walk through the radiation zone.
D) Fusion in the Sun’s core creates neutrinos.
E) The Sun does not emit neutrinos.

D) Fusion in the Sun’s core creates neutrinos.
How can we measure the strength of magnetic fields on the Sun?

A) by observing the sizes of sunspots: Bigger sunspots mean a stronger field
B) by observing auroras here on Earth
C) by looking for the splitting of spectral lines in the Sun’s spectrum
D) only by using sophisticated computer models because there are no observational ways of measuring magnetic field strength

C) by looking for the splitting of spectral lines in the Sun’s spectrum
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 make a computer model of the Sun’s interior that allows us to predict the observable properties of the Sun.
C) We can probe the interior of the Sun by studying the vibrations in its photosphere.
D) We can study solar neutrinos.

A) We can send a space probe into the Sun’s photosphere.
The Sun will exhaust its nuclear fuel in about ________.

A) 5 billion years
B) 5000 AD
C) 50 billion years
D) 5 million years

A) 5 billion years
Which of the following correctly describes how the process of gravitational contraction can make a star hot?

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

D) When a star contracts in size, gravitational potential energy is converted to thermal energy.
Energy balance in the Sun refers to a balance between ________.

A) the force of gravity pulling inward and the force due to pressure pushing outward
B) 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
C) the amount of energy the Sun radiates into space and the amount of energy that reaches Earth
D) the mass that the Sun loses each second and the amount of mass converted into energy each second

B) 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
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, corona, radiation zone, convection zone, photosphere, chromosphere
C) core, radiation zone, convection zone, corona, chromosphere, photosphere
D) core, radiation zone, convection zone, photosphere, chromosphere, corona

D) core, radiation zone, convection zone, photosphere, chromosphere, corona
What is the solar wind?

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

A) a stream of charged particles flowing outward from the surface of the Sun
What happens to energy in the Sun’s convection zone?

A) Energy is produced in the convection zone by thermal radiation.
B) Energy is transported outward by the rising of hot plasma.
C) Energy is produced in the convection zone by nuclear fusion.
D) Energy slowly leaks outward through the radiative diffusion of photons that repeatedly bounce off ions and electrons.

B) Energy is transported outward by the rising of hot plasma.
What would happen to the core of the sun if its temperature rose slightly?

A) The rate at which fusion occurs would decrease, leading to a contraction of the core, which would in turn cause a further temperature rise.
B) The rate at which fusion occurs would increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down.
C) The rate at which fusion occurs would increase, leading to a contraction of the core, which would in turn cause the temperature to rise even further.
D) The rate at which fusion occurs would decrease, leading to an expansion of the core, which would in turn cause the temperature to drop back down.

B) The rate at which fusion occurs would increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down.
Which of the following is not a method astronomers use to determine the physical conditions inside the Sun?

A) building mathematical models that use the laws of physics
B) detecting solar neutrinos generated in the Sun’s core
C) measuring Doppler shifts to observe solar vibrations
D) observing X-ray images of the solar interior using satellites
E) both detecting solar neutrinos generated in the Sun’s core and measuring Doppler shifts to observe solar vibrations

D) observing X-ray images of the solar interior using satellites
Studies of solar vibrations have revealed that

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

B) our mathematical models of the solar interior are fairly accurate.
How do we know how old the Sun is?

A) from its speed and distance from us
B) from ages of solar system meteorites, based on radioactive elements
C) from calculating its fuel supply and how fast it is using it up
D) from Newton’s version of Kepler’s third law and the orbits of the planets

B) from ages of solar system meteorites, based on radioactive elements
Which of the following statements about the Sun is an inference from a model, not an observation?

A) The convection zone is cooler than the radiation zone.
B) The corona is hotter than the photosphere.
C) The photosphere emits visible light.
D) The Sun emits neutrinos.

A) The convection zone is cooler than the radiation zone.
The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last.

White Dwarf
Main-sequence Star
Red Giant
Contracting Cloud of gas and dust
planetary nebula
Protostar

Contracting cloud of gas and dust
protostar
main-sequence star
red giant
planetary nebula
white dwarf
Provided following are various elements that can be produced during fusion in the core of a high mass main sequence star. Rank these elements based on when they are produced, from first to last.

oxygen
helium
iron
carbon

helium
carbon
oxygen
iron
Which event marks the beginning of a supernova?

A) The onset of helium burning after a helium flash
B) The sudden initiation of the CNO cycle
C) The beginning of neon burning in an extremely massive star
D) The sudden collapse of an iron core into a compact ball of neutrons

D) The sudden collapse of an iron core into a compact ball of neutrons
A spinning neutron star has been observed at the center of a ________.

A) red supergiant
B) supernova remnant
C) planetary nebula
D) protostar

B) supernova remnant
The interstellar clouds called molecular clouds are ________.

A) clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide
B) the clouds in which elements such as carbon, nitrogen, and oxygen are made
C) the cool clouds in which stars form
D) the hot clouds of gas expelled by dying stars

C) the cool clouds in which stars form
Most interstellar clouds remain stable in size because the force of gravity is opposed by ________ within the cloud.

A) thermal pressure
B) stellar winds
C) degeneracy pressure
D) radiation pressure

A) thermal pressure
Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?
A) Visible light
B) Ultraviolet
C) Infrared
D) Blue light
C) Infrared
What kind of gas cloud is most likely to give birth to stars?

A) A cold, low-density gas cloud
B) A hot, low-density gas cloud
C) A cold, dense gas cloud
D) A hot, dense gas cloud

C) A cold, dense gas cloud
When does a protostar become a main-sequence star?

A) When it becomes luminous enough to emit thermal radiation
B) At the instant that the first hydrogen fusion reactions occur in the protostar’s core
C) When a piece of a molecular cloud first begins to contract into a star
D) When the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space

D) When the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space
Approximately what core temperature is required before hydrogen fusion can begin in a star?

A) 1 billion K
B) 10,000 K
C) 10 million K
D) 10 billion K
D) 10 trillion K

C) 10 million K
What is the approximate range of masses that newborn main sequence stars can have?

A) 0.1 to 300 solar masses
B) 0.001 to 10 solar masses
C) 0.1 to 1,000 solar masses
D) 0.001 to 300 solar masses
E) 0.1 to 10 solar masses

A) 0.1 to 300 solar masses
What happens when a main-sequence star exhausts its core hydrogen fuel supply?

A) The entire star shrinks in size.
B) The core immediately begins to fuse its helium into carbon.
C) The core shrinks while the rest of the star expands.
D) The star becomes a neutron star.

C) The core shrinks while the rest of the star expands.
What is the CNO cycle?

A) The set of fusion reactions that have produced all the carbon, nitrogen, and oxygen in the universe
B) The process by which helium is fused into carbon, nitrogen, and oxygen
C) A set of steps by which four hydrogen nuclei fuse into one helium nucleus
D) The process by which carbon is fused into nitrogen and oxygen

C) A set of steps by which four hydrogen nuclei fuse into one helium nucleus
Why is iron significant to understanding how a supernova occurs?

A) Iron cannot release energy either by fission or fusion.
B) Iron is the heaviest of all atomic nuclei, and thus no heavier elements can be made.
C) The fusion of iron into uranium is the reaction that drives a supernova explosion.
D) Supernovae often leave behind neutron stars, which are made mostly of iron.

A) Iron cannot release energy either by fission or fusion.
Which of the following masses separates low mass stars from high mass stars?

A) About 2 solar masses
B) About 150 solar masses
C) About 50 solar masses
D) About 0.08 solar masses
E) About 1 solar mass

A) About 2 solar masses
No stars are expected with masses greater than 150 times our Sun because

A) they would be too massive for hydrogen fusion to occur in their cores.
B) they would shine exclusively at X-ray wavelengths and would be difficult to detect.
C) they would generate so much power that they would blow themselves apart.
D) molecular clouds do not have enough material to form such massive stars.
E) they would fragment into binary stars because of their rapid rotation.

C) they would generate so much power that they would blow themselves apart.
What percentage of a star’s total lifetime (before it becomes a white dwarf or explodes in a supernova) is spent on the main sequence?

A) 10%
B) 50%
C) 90%
D) 20%
E) 100%

C) 90%
What happens when a star like the sun exhausts its core hydrogen supply?

A) It contracts, becoming hotter and brighter.
B) It expands, becoming bigger but dimmer.
C) Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
D) It contracts, becoming smaller and dimmer.
E) Its core contracts, but its outer layers expand and the star becomes bigger but cooler and therefore remains at the same brightness.

C) Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
What does the CNO cycle and the hydrogen proton-proton cycle have in common? Choose the best answer to the question.

A) They both trigger at the same temperature.
B) They are both cycles in star lives.
C) They both are ways to fuse hydrogen nuclei to make helium.
D) They are both nuclear reactions; the CNO cycle makes carbon, nitrogen, and oxygen, and the proton cycle makes helium

C) They both are ways to fuse hydrogen nuclei to make helium.
Choose from the list below for the following question.

A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction

Which method of energy generation is used by the Sun today?

A. H fusion by the proton-proton chain
Choose from the list below for the following question.

A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction

Which method of energy generation provides the source of energy for a protostar?

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

A) the distance to the nearest star besides the Sun
B) the Earth-Sun distance
C) the Sun’s mass
D) the month in which the star is observed

B) the Earth-Sun distance
Which of the following is a valid way of demonstrating parallax for yourself?

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

C) Hold up your hand in front of your face, and alternately close your left and right eyes.
What is the cause of stellar parallax?
Stellar parallax is caused by

A) the gradual motion of stars in the local solar neighborhood.
B) the varying speed of Earth in its orbit around the Sun.
C) the gradual change in the patterns of the constellations over thousands of years.
D) Earth’s orbit around the Sun.

D) Earth’s orbit around the Sun.
Approximately what is the parallax angle of a star that is 20 light-years away?

A) 0.16 arcsecond
B) 0.33 arcsecond
C) 0.0072 arcsecond
D) 4.5×10−5 arcsecond

A) 0.16 arcsecond
Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?

A) 8.7 light-years
B) 2.1 light-years
C) 3.3 light-years
D) 1 light-year

C) 3.3 light-years
Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.

the hottest and most luminous stars
very hot but very dim
very cool but very luminous
the sun for example
found in the upper right of the H-R diagram
not much larger in radius than earth
the majority of stars in our galaxy

Categories:
Red giant or supergiant stars
Main-sequence stars
white dwarfs

Red giant or supergiant stars:
found in the upper right of the H-R diagram
very cool but very luminous

Main-sequence stars:
the majority of stars in our galaxy
the sun for example
the hottest and most luminous stars

White Dwarfs:
very hot but very dim
not much larger in radius than earth

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

A) hotter and larger in radius
B) cooler and larger in radius
C) cooler and smaller in radius
D) hotter and smaller in radius

B) cooler and larger in radius
Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

A) hotter and larger in radius
B) cooler and larger in radius
C) cooler and smaller in radius
D) hotter and smaller in radius

D) hotter and smaller in radius
All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?

A) Its apparent brightness and its luminosity
B) Its age and its location in the galaxy
C) Its apparent brightness and its distance
D) Its mass and its stage of life
E) Its mass and its surface temperature

D) Its mass and its stage of life
Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore:

A) Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.
B) Both stars have the same luminosity, but the apparent brightness of Star B is twice that of Star A.
C) Both stars have the same apparent brightness, but the luminosity of Star B is four times that of Star A.
D) Both stars have the same luminosity, but the apparent brightness of Star A is four times that of Star B.

A) Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.
Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude?

A) Sirius has a higher surface temperature than Rigel.
B) Rigel has a higher surface temperature than Sirius.
C) Rigel has a higher core temperature than Sirius.
D) Sirius has a higher core temperature than Rigel.

B) Rigel has a higher surface temperature than Sirius.
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 increase by a factor of 3.
B) Its apparent brightness will decrease 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 9.

B) 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) Determine both the star’s distance and luminosity from its apparent brightness.
C) Calculate the star’s luminosity if we know its distance, or calculate its distance if we know its luminosity.
D) Calculate the star’s surface temperature if we know either its luminosity or its distance.

C) Calculate the star’s luminosity if we know its distance, or calculate its distance if we know its luminosity.
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) We know the star’s luminosity and distance.
B) The star is of spectral type A.
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.
On an H-R diagram, stellar masses ________.

A) can be determined for main sequence stars but not for other types of stars
B) are greatest in the lower left and least in the upper right
C) decrease from upper left to lower right
D) are impossible to determine

A) can be determined for main sequence stars but not for other types of stars
What is a white dwarf?

A) A main sequence star of spectral type F, which tends to look white in color
B) The remains of a star that ran out of fuel for nuclear fusion
C) It is a star that follows a period-luminosity relation.
D) It is a type of star that produces energy by gravitational contraction.

B) The remains of a star that ran out of fuel for nuclear fusion
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

A) time they are formed
B) color they are formed with
C) location where they are formed
D) luminosity they are formed with
E) mass they are formed with

E) mass they are formed with
An O-star has a hotter surface temperature than the Sun. Therefore, compared to the Sun,

A) it emits at about the same wavelengths as the Sun (similar peak) but it is much fainter.
B) it emits at about the same wavelengths as the Sun (similar peak) but it is much brighter.
C) its emission peaks in the blue part of the spectrum.
D) its emission peaks in the infrared part of the spectrum.

C) its emission peaks in the blue part of the spectrum.