Astronomy Final Exam
supermassive black hole
A black hole with a mass millions to billions times that of our Sun.
rotation curve
A diagram that plots the rotation velocity of stars or gas clouds against their distance from the center of the galaxy and summarizes the results of orbital velocity measurements.
radio galaxy
A galaxy that emits unusually large quantities of radio waves; thought to contain an active galactic nucleus powered by a supermassive black hole.
central dominant galaxies
A giant elliptical galaxy found in the center of a dense cluster of galaxies, apparently formed by the merger of individual galaxies.
Yes because asteroids exist because they contain rock and metal due to their formation within the frostline where metals and rocks can condense, and comets exist because they were formed outside of the frostline where ice can condense. Thus, asteroids wouldn't have their typical composition if they formed in the hypothetical solar system.
A hypothetical solar system has many rocky asteroids and many icy comets. Most of the comets orbit in the inner solar system while the asteroids orbit in far-flung regions like the Kuiper belt and the Oort cloud. Would this solar system surprise you? Why or why not?
radar ranging
A method that astronomers use to measure the AU from Earth to another object in which radio waves are transmitted from Earth and bounced off the other object.
Hubble's Constant
A number that expresses the current rate of expansion of the universe.
D
A planet is detected via the Doppler technique. The repeating pattern of the stellar motion tells us A) the planet's size. B) the planet's mass. C) the planet's density. D) the orbital period of the planet. E) the orbital eccentricity of the planet.
Tully-Fisher relation
A relationship among spiral galaxies showing that the faster a spiral galaxy's rotation speed, the more luminous it is; it is important because it allows us to determine the distance to a spiral galaxy once we measure its rotation rate and apply the luminosity-distance formula.
B
A scientific theory is... A) a reasonable but unconfirmed suggestion B) a well-confirmed network of ideas that explains observations of nature C) any statement that can't be disproven D) an idea that has never been contradicted E) a guess made by a scientist
D
A skater can spin faster by pulling her arms closer to her body or spin slower by spreading her arms out from her body. This is due to A) the law of gravity. B) Newton's third law. C) conservation of momentum. D) conservation of angular momentum. E) conservation of energy.
E
A star's luminosity is the A) apparent brightness of the star in our sky. B) surface temperature of the star. C) lifetime of the star. D) total amount of light that the star will radiate over its entire lifetime. E) total amount of light that the star radiates each second.
standard candle
A term that is meant to suggest a light source of a known, standard luminosity. This can only work if astronomers have a way of knowing the luminosity without measuring its apparent brightness and distance.
D
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-sized particle from a comet E) microscopic particle of interstellar dust.
C
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 original solar nebula happened to be disk-shaped by chance. B) Any planets that once orbited in the opposite direction or a different plane were ejected from the solar system. C) The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk. D) 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. E) Luck explains it, as we would expect that most other solar systems would not have all their planets orbiting in such a pattern.
E
According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them will A) increase by a factor of 3. B) decrease by a factor of 3. C) decrease by a factor of 6. D) increase by a factor of 9. E) decrease by a factor of 9.
E
After a supernova event, what is left behind? A) always a white dwarf B) always a neutron star C) always a black hole D) either a white dwarf or a neutron star E) either a neutron star or a black hole
1. How hot the surface area of a distant object is depending on the color of light we observe. 2. The chemical composition of a distant object depending on the spectral lines we observe.
Ancient people observed differences in the color and brightness of objects in the sky. Today, we extract much more information from light than thus. Give two other pieces of information we can learn from light.
E
At the center of the Sun, fusion converts hydrogen into A) hydrogen compounds. B) plasma. C) radiation and elements like carbon and nitrogen. D) radioactive elements like uranium and plutonium. E) helium, energy, and neutrinos.
Far from just sitting still, we on Earth are moving relative to the Sun, planets, stars, and even other galaxies. The rotation of Earth causes the most noticeable changes in the sky. This motion around Earth's axis causes the Sun and stars to appear to rise and set, producing what we call a "day." The revolution of Earth about the Sun produces the monthly changes of the constellations, the seasonal weather changes due to Earth's tilt, and the parallax of some stars. The precession of Earth's axis, a very slow movement that has a period of 26,000 years, causes the movement of the North Star, and the changing position of the equinoxes and solstices.
Based on the idea of "spaceship Earth," why are we not just sitting here motionless?
B
Black holes, by definition, cannot be observed directly. What observational evidence do scientists have of their existence? A) theoretical models B) graviratioal interactions with other objects C) space is, overall, very black D) we have sent spacecraft to nearby black holes E) we have detected neutrinos from them
In cold, dense molecular clouds, gravity brings material together. As gas moves inwards it converts gravitational potential energy to thermal energy and warms up. Once the cloud becomes so dense that the thermal radiation cannot escape, the temperature rises rapidly, nuclear fusion begins and the dense core becomes a protostar. As the cloud has collapsed from a large size to a small size, it must spin very fast to conserve angular momentum. This results in the formation of a protostellar disk around the protostar. Planets may form in this disk as the star continues to grow. Eventually stellar winds and jets clear away the surrounding gas and a newly formed star emerges.
Briefly describe how a star forms
A large impact could send huge quantities of dust into the stratosphere, where it would block out sunlight for several years. The surface cools and plants die for lack of sunlight. Effects propagate through the food chain, leading to death and extinction on an enormous scale.
Briefly describe how an impact could lead to a mass extinction.
Each element is unique and has its own properties. Thus, the lines in a spectroscope will be unique depending on the elements in the gasses.
Briefly describe how spectral lines, the colorful lines seen in a spectroscope from glowing gasses, are useful in determining the chemical composition of their source.
Stars are formed from gravitational contractions of molecular clouds. High-mass stars explode into supernova, and they release bubbles of the elements they created. The bubbles slowly transform into hydrogen in molecular clouds, thus starting the cycle over again.
Briefly describe the star-gas-star cycle.
The two key pieces of evidence that support the Big Bang theory are the cosmic background radiation and the observed helium content of the universe. The cosmic background radiation consists of photons arriving at Earth directly from the end of the era of nuclei. The radiation came from the heat of the universe and should have a thermal radiation spectrum with a peak wavelength corresponding to 3,000 K, the temperature the universe was at the end of that era. Since the universe has expanded by a factor of about 1,000 since that time, we observe the radiation with a peak wavelength of about a millimeter, corresponding to a temperature of 2.73 K. The Big Bang theory predicts that the universe should have had a composition of 75 percent hydrogen and 25 percent helium by mass at the end of the era of nucleosynthesis. The Milky Way's helium fraction is about 28 percent, and no galaxy has a helium fraction lower than 25 percent.
Briefly describe the two key pieces of evidence that support the Big Bang theory.
1. Recollapsing universe: the density of the universe is greater than critical. Gravity will eventually reverse the expansion, resulting in a "Big Crunch." 2. Critical universe: the density of the universe is equal to the critical density. Gravity just balances the expansion which slows increasingly down toward zero as time progresses. 3. Coasting universe: the density of the universe is less than the critical density. The expansion overwhelms the attractive force of gravity and the universe expands without limit. 4. Accelerating universe: a mysterious repulsive force that acts against gravity on large scales causes the universe to expand with ever-increasing speed.
Briefly describe the two of the four possible expansion patterns of the universe.
Because light can only travel so far at a time, it takes years for the light from distant galaxies to reach Earth. For example, if someone on Earth observed a star that was 1 billion light years away, the light they saw would be 1 billion years old.
Briefly describe what is meant by the statement "The farther away we look in the distance, the further back we look in time."
As he approached the black hole, he would be stretched by tidal forces, his time would run slow, and light coming from him would be redshifted. The closer he got to the event horizon, the slower time would run. You would never see him cross the event horizon, but he would disappear from view when his light became redshifted out of the range of detection.
Briefly describe what you would see if your friend plunged into a black hole.
The Sun formed from a cloud of gas. As it contracted, its gravitational potential energy was converted to thermal energy. The Sun continued to contract until the core became hot enough to sustain nuclear fusion.
Briefly explain how the Sun became hot enough for nuclear fusion.
High mass stars are born with more mass and higher amounts of hydrogen, so they undergo nuclear fusion faster due to their higher temperatures that are caused by their higher masses.
Briefly explain why high mass stars have shorter lifetimes than low mass stars.
The star-gas-star cycle gradually enriches the interstellar medium with heavy elements. Therefore, stars that formed early in the history of the galaxy were formed before much enrichment from supernova events could take place. Stars that formed more recently were formed from material that had been enriched by the many previous generations of stars.
Briefly explain why stars that formed early in the history of the galaxy contain a smaller proportion of heavy elements than stars that formed more recently.
B
By mass, the interstellar medium in our region of the Milky Way consists of A) 70% Hydrogen, 30% Helium. B) 70% Hydrogen, 28% Helium, 2% heavier elements. C) 70% Hydrogen, 20% Helium, 10% heavier elements. D) 50% Hydrogen, 50% Helium. E) 50% Hydrogen, 30% Helium, 20% heavier elements
period-luminosity relation
Cepheids obey this, which allows us to determine a Cepheid's luminosity simply by measuring the time period over which its brightness varies.
The celestial sphere is a fictional concept that the ancient Greeks conjured as a way to describe what we see from Earth. Thus, because it doesn't actually exist, a spaceship couldn't travel to it.
Consider the following statement, and explain whether or not it is sensible: If you had a very fast spaceship, you could travel to the celestial sphere in about 100 years.
galactic wind
Consist of low-density, but extremely hot, gas.
supercluster
Consists of many clusters of galaxies, groups of galaxies, and individual galaxies and are the largest known structures in the universe.
D
Degeneracy pressure is the source of pressure that stops the crush of gravity in all of the following except A) a brown dwarf B) a white dwarf C) a neutron star D) a very massive main sequence star E) the central core of the Sun after hydrogen fusion ceases but before helium fusion begins.
1. We've realized that our solar system may be the exception to the general rule of solar system formation because it's quite different from extrasolar worlds we've observed. 2. We've realized that our solar system is relatively young compared to other worlds we've observed.
Describe two impacts the discovery of extrasolar planets has had for understanding the origin of our own solar system.
D
Earth is made mostly of metals and rocks. Where did this material come from? A) It was produced in the Big Bang. B) It was created by chemical reactions in interstellar space. C) It was produced by nuclear fusion in stars. D) It was made by our Sun. E) It was made by nuclear fission of uranium and other radioactive materials.
particle era
Era in which antimatter particles were annihilated by matter particles.
electroweak era
Era in which electromagnetism and the weak force became distinct.
era of nucleosynthesis
Era in which fusion of protons and neutrons into helium ceased.
era of atoms.
Era in which galaxies began to form.
GUT era
Era in which gravity became distinct and may have ended in a rapid expansion called inflation.
era of nuclei
Era in which hydrogen nuclei captured all the free electrons, forming hydrogen atoms.
For every orbit that Ganymede completes around Jupiter, Europa completes exactly two orbits and Io completes exactly four. Therefore, all three planets line up for every orbit of Ganymede, and Io and Europa line up twice each Ganymede orbit. The gravitational tugs from their sister moons add up over time, and these tugs are always in the same direction. Therefore, the moons' orbits become slightly elliptical over time.
Explain how the resonance among Io, Europa, and Ganymede makes their orbits slightly elliptical.
Scientists believe Io must have an ongoing process that heats its interior that our Moon doesn't have. They believe this process is called tidal heating, which occurs from a tidal force from Jupiter. Although Earth also exerts this force on the Moon, Jupiter is much more massive and exerts the force more, which ultimately allows the heating to occur.
Explain why and how Io is the most volcanically active planet in our solar system despite being about the same size as our geologically dead Moon.
B
From lab measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 121.8 nm. What can we conclude? A) the star is moving toward us. B) the star is moving away from us. C) the star is getting hotter. D) the star is getting colder. E) the star is actually a planet.
starburst galaxies
Galaxies in which stars are forming at an unusually high rate.
irregular galaxies
Galaxies that appear neither disk-like nor rounded.
elliptical galaxies
Galaxies that are redder, more rounded, and often elongated. They contain very little cool gas and dust, though they often contain very hot ionized gas.
spiral galaxies
Galaxies that look like flat white disks with yellowish bulges at their centers. The disks are filled with cool gas a dust, interspersed with hotter ionized gas, and usually display beautiful arms.
•Computer simulations of the Moon's formation •Composition similar to Earth's crust •Moon is depleted of easily vaporized materials as expected from the heat of an impact •Signatures of giant impacts on other planets
Give 2 pieces of evidence supporting the giant impact theory of the Moon
•Counterclockwise rotation of Venus •Large size of Earth's Moon •Extreme axis tilt of Uranus •Retrograde rotation of Triton around Neptune
Give 3 exceptions to the general patterns in the solar system
D
Grass (that is healthy) looks green because A) it emits green light and absorbs other colors. B) it absorbs green light and emits other colors. C) it transmits green light and emits other colors. D) it reflects green light and absorbs other colors.
Using the largest telescope in the world at the time, he identified individual cepheid variable stars in the Andromeda Galaxy. He was then able to use the period-luminosity relation for cepheids to determine their luminosities and hence their distances, proving that Andromeda is much too far away to be a part of the Milky Way.
How did Hubble prove that galaxies lie far beyond the Milky Way?
They formed as gravity pulled together regions of the universe that were ever so slightly denser than their surroundings. Gas collected in protogalactic clouds, and stars began to form as the gas cooled.
How did galaxies form?
It held that the planets moved along small circles that moved on larger circles around Earth.
How did the Ptolemaic model explain the apparent retrograde motion of the planets?
Combining distance measurements with velocity measurements tells us Hubble's constant, and the inverse of Hubble's constant tells us how long it would have taken the universe to reach its present size if the expansion rate had never changed. Based on Hubble's constant and estimates of how it has changed with time, we now estimate the age of the universe at about 14 billion years.
How do distance measurements tell us the age of the universe?
in groups that contain up to several dozen galaxies
How do spiral galaxies tend to collect together?
B
How do we know that there is much more mass in the halo of our galaxy than in the disk? A) There are so many globular clusters in the halo that their total mass is greater than the mass of stars in the disk. B) Stars in the outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass were concentrated in the disk. C) Although the question of mass in the halo was long mysterious, we now know it exists because we see so many brown dwarfs in the halo. D) The recent discovery of photinos, combined with theoretical predictions, tells us that there must be a huge mass of photinos in the halo. E) We don't know that there is more mass in the halo; it is only a guess based on theory.
E
How do we know what goes on under the surface of the Sun? A) We have X-ray images from satellites of the interior of the Sun. B) Astronomers create mathematical models that use the laws of physics, the Sun's observed composition and mass, and computers to predict internal conditions. C) We have sent probes below the surface of the Sun. D) By measuring Doppler shifts, we observe vibrations of the Sun's surface that are created deep within the Sun. E) both B and D
It claims that the sky is dark at night because the universe has a finite age, which means we can only see a finite number of stars in the sky.
How does the Big Bang theory disprove Olber's paradox?
Distances between galaxies are always changing because of the expansion of the universe. It is therefore best to express the distance to a faraway galaxy in terms of lookback time, which is the time is has taken for the galaxy's light to reach us. The expansion of the universe during that time stretches the light coming from the galaxy, leading to a cosmological redshift directly related to the galaxy's lookback time.
How does the universe's expansion affect our distance measurements?
About 3000 years
How long would it take to count all the stars in the Milky Way Galaxy at a rate of one star per second?
We would no longer have seasons, because the Sun's light would hit at the same angle all throughout the year, depending only on where you lived. The slight change in distance between Earth and the Sun during the year would not produce much of an effect.
If Earth's axis had no tilt, would we still have seasons? Why or why not?
Yes because Mercury is a very desolate planet with no observed tectonic activity. In fact, it shows little evidence of geological change.
If we placed seismographs on the surface of Mercury and recorded frequent, violent earthquakes, would you be surprised? Why or why not?
50 m/s
If you drop a rock from a great height, about how fast will it be falling after 5 seconds, neglecting air resistance?
E
If you drop a rock from a great height, about how fast will it be falling after 5 seconds, neglecting air resistance? A) it depends how heavy it is B) it depends what shape it is C) 10 m/s D) 15 m/s E) 50 m/s
E
If you represented each star by a grain of sand, how much sand would it take to represent all the stars in the universe? A) all the sand in a typical playground sandlot B) all the sand on Miami Beach C) all the sand on the beaches of California D) all the sand on the beaches in the United States E) more than all the sand on all the beaches on Earth
C
If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe? A) ultraviolet B) visibile C) infrared D) X-ray E) gamma-ray
B
If you were to come back to our Solar System in 6 billion years, what might you expect to find? A) a red giant star B) a white dwarf C) a rapidly spinning pulsar D) a black hole E) Everything will be pretty much the same as it is now
sheroidal component
In a spiral galaxy, the disk and the halo together make up this, which is named for its rounded shape.
disk component
In a spiral galaxy, this is a flat disk in which stars follow orderly, nearly circular orbits around the galactic center. This always contains an interstellar medium of gas and dust.
1. It has a life-sustaining greenhouse effect that no other body has. 2. Its moon is extremely large for a terrestrial planet. 3. It has liquid water on the surface.
List at least 3 things that make Earth unique in the solar system.
Some of the key properties of good standard candles include little statistical scatter in brightness; high luminosity, so they can be seen at a great distance; and relative commonness, so they can be found in many objects.
List at least two qualities that would tend to make a type of astronomical object useful as a standard candle.
1. Radar ranging to close objects 2. Parallax measurements of nearby stars 3. Standard candles to find extremely far away objects
List three methods we use to find the distance to objects in space.
Helium fuses into carbon by combining 3 helium nuclei, and it bypasses 3, 4, and 5.
Lithium, beryllium, and boron are elements with atomic numbers 3, 4, and 5, respectively. Even though they are 3 of the 5 simplest elements, why are they rare compared to many heavier elements?
Hubble's Law
Mathematically expresses the idea that more distant galaxies move away from us faster.
dark matter
Matter than we infer to exist from the gravitational effects but from which we have not detected any light; it apparently dominates the total mass of the universe.
B
Most of the planets discovered around other stars A) are more massive than Earth and orbit very far from the star. B) are more massive than Earth and orbit very close to the star. C) are less massive than Earth and orbit very far from the star. D) are less massive than Earth and orbit very close to the star. E) are found around neutron stars.
Conservation of energy, momentum, or angular momentum.
Name 2 quantities that are conserved (i.e. Conservation of ...)
•Astrometric •Doppler shift •Transit •Gravitational lensing •Dust disk disturbances
Name 3 methods of planet detection
•Impact Cratering •Volcanism •Tectonics •Erosion
Name 3 of the 4 major geological processes
1. The planets orbit the Sun on the same plane due to the conservation of angular momentum that formed a disk in the early days of formation. 2. The terrestrial planets are close to the Sun because they formed within the frostline. 3. The jovian planets are far away from the Sun because they formed outside of the frostline.
Name 3 patterns of motion or planetary arrangement/location that a theory of solar system formation should be able to explain.
dark energy
Name sometimes given to energy that would be causing the expansion of the universe to accelerate.
1. recollapsing universe 2. critical universe 3. coasting universe 4. accelerating universe
Name the 4 expansion patterns.
The strong force is able to overcome the electromagnetic repulsion between the positively charged nuclei. The strong force overpowers the electromagnetic force over very small distances, so nuclear fusion works because it pushes positively charged nuclei close enough together for the strong force to overpower their repulsion.
Nuclear fusion occurs in the Sun when hydrogen nuclei combine to form helium. Given that the hydrogen nuclei contain the same positive charge and that like charges repel one another, briefly explain how this process occurs.
C
On the main sequence, stars obtain their energy A) from chemical reactions. B) from gravitational contraction. C) by converting hydrogen to helium. D) by converting helium to carbon, nitrogen, and oxygen. E) from nuclear fission.
D
On the scale of the cosmic calendar, in which the history of the universe is compressed to 1 year, how long has human civilization (i.e. since ancient Egypt) existed? A) About half a year B) About a month C) A few hours D) A few seconds E) Less than a millionth of a second
baryonic matter
Ordinary matter made from atoms.
baryons
Particles, including protons and neutrons, that are made from three quarks.
D
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ? A) location where they are formed B) time they are formed C) luminosity they are formed with D) mass they are formed with E) color they are formed with
MACHO
Stands for massive compact halo objects and represents one possible form of dark matter in which the dark objects are relatively large, like planets or brown dwarfs.
To fall to Earth, the satellite must lose some of its orbital energy. In low-Earth orbit, this can happen because the earth's atmosphere extends to high altitudes and exerts some atmospheric drag on the satellite.
Suppose a satellite is in a low-Earth orbit. Is it possible that the satellite will eventually fall to the ground? Why or why not?
C
Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest? A) the one that is reddest in color B) the one that is bluest in color C) the one that is farthest away D) the one that is closest to us E) the one that appears smallest in size
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.
Suppose that, for some unknown reason, the core of the Sun suddenly became hotter. Describe what would happen.
A star made of only helium and hydrogen would have to be among the first generation of stars ever born, arising out of the primordial mix of elements that came from the Big Bang. The oldest stars we know about are over 12-15 billion years old—a star made of only helium and hydrogen would have to be at least this old. (No such star has ever been discovered.)
Suppose you discovered a star made purely of hydrogen and helium. How old do you think it would be? Explain
The ice melts into liquid, then evaporates into gas. At higher temperatures, the water molecules dissociate into atoms. At very high temperatures, the atoms are ionized.
Suppose you have a chunk of water ice. Describe what happens to it, in terms of phases, as you raise the temperature to millions of degrees.
D
Suppose you have two protons near each other. Because of the electromagnetic force, the two protons will A) collide B) remain stationary C) attract each other D) repel each other E) join together to form a nucleus
E
Suppose you heat up an oven and boil a pot of water. Which of the following explains why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven? A) the oven has a higher temperature than the water B) the water has a higher temperature than the oven C) the oven has a higher heat content than the water D) the molecules in the water are moving faster than the molecules in the oven E) the water has a higher heat content than the oven
D
Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: think about the laws of thermal radiation.) A) The red star is more massive than the blue star. B) The blue star is more massive than the red star. C) The blue star is farther away than the red star. D) The blue star has a hotter surface temperature than the red star. E) The red star has a hotter surface temperature than the blue star.
The spacecraft was accelerated because a change in velocity occurred. Any change in velocity results in acceleration, and because the speed increased, the velocity changed.
The New Horizons spacecraft launched on January 19, 2006 from Cape Canaveral going from an initial speed of 0 km/s to a speed of about 16 km/s in order to break orbit and leave Earth. Was the spacecraft accelerated? Why or why not?
lookback time
The amount of time that has passed since light we see from a distant object was emitted. That is, if an object has a lookback time of 400 million years ago, we are seeing it as it looked 400 million years ago.
quasars
The brightest type of active galactic nuclei.
D
The center of mass of a binary star system is A) the center of the most massive of the two stars B) the center of the least massive of the two stars C) the point halfway in between them D) the point at which the two objects would balance if they were somehow connected E) the average mass of the two stars
D
The composition of a planet can be determined by A) Doppler technique B) astrometric measurements C) transit observations D) spectra E) all of the above
C
The core of the Sun is A) at the same temperature and density as the surface B) at the same temperature but denser than the surface C) hotter and denser than the surface D) constantly rising to the surface through convection E) composed of iron
era of galaxies
The current era we're in.
gravitational equilibrium
The delicate balance between two opposing forced (pressure and gravity) within the Sun.
voids
The empty regions between chains and sheets of galaxies.
Plank era
The era when the four forces may have all behaved as one.
cosmological principle
The idea that matter in the universe is evenly distributed, without a center or an edge.
cepheid variable stars
The most useful bright stars for measuring the distances to galaxies that vary in brightness in our sky, alternatively becoming dimmer and brighter with periods ranging from a few days to a few months.
critical density
The precise density marking the dividing line between eternal expansion and eventual collapse.
cosmological redshifts
The redshifts we see from distant galaxies, caused by the fact that expansion of the universe stretches all the photons within it to longer, redder wavelengths.
galaxy evolution
The study of how galaxies form and develop in our expanding universe.
cosmology
The study of the overall structure and evolution of the universe.
main-sequence fitting
The technique of determining distances by comparing main sequences in different star clusters.
B
The three principal sources of 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.
plank time
The time when the universe was 10^-43 second old, before which random energy fluctuations were so large that our current theories are powerless to describe what might have been happening.
active galactic nuclei
The unusually luminous centers of some galaxies, thought to be powered by accretion onto supermassive black holes.
gravitational lenses
These bend light beams that pass nearby.
Olber's paradox
This tells us that if the universe were infinite, unchanging, and filled with stars, the sky would be everywhere as bright as the surface of the Sun, and it would not be dark at night.
B
We can learn a lot about the properties of a star by studying its spectrum. All of the following statements are true except one. Which one? A) The peak of the star's thermal emission tells us its temperature: Hotter stars peak at shorter (bluer) wavelengths. B) The total amount of light in the spectrum tells us the star's radius. C) We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals. D) We can look at Doppler shifts of spectral lines to determine the star's speed toward or away from us.
parallax
We use this to measure the distance to nearby stars by observing how their positions change, relative to background stars, as Earth orbits the Sun.
1. Plank era 2. GUT era 3. electroweak era 4. particle era 5. era of nucleosynthesis 6. era if nuclei 7. era of atoms 8. era of galaxies
What are the eras of the universe?
1. thermal pressure 2. radiation pressure 3. degeneracy pressure
What are the three types of pressure that can push against the inward force of gravity?
(1) Thermal pressure occurs when the particles inside a star are heated enough so that their random motions cause an outward pressure. The two energy sources of internal thermal pressure are gravitational contraction, found in protostars and when a star has used up a fusionable material in its core, and nuclear fusion, which can occur in the core or in a shell of a star. (2) Degeneracy pressure arises from the idea of quantum mechanics that two electrons (or neutrons) cannot occupy the same state. Degeneracy pressure occurs in the cores of low-mass stars before a helium flash, maintains equilibrium in white dwarfs and neutron stars, and may be present immediately before a supernova event. (3) Radiation pressure exists only in massive stars where fusion rates are so high that photons transfer momentum to the surrounding gas and apply a third kind of pressure.
What are the three types of pressure that can push against the inward force of gravity? Explain what causes each pressure and where it would be likely to occur.
As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse.
What causes the radio pulses of a pulsar?
C
What do astronomers mean when they say that we are all "star stuff"? A) that life would be impossible without energy from the Sun B) that Earth formed at the same time as the Sun C) that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores D) that the Sun formed from the interstellar medium: the "stuff" between the stars E) that the Universe contains billions of stars
D
What do the structures of Stonehenge, the Templo Mayor, and the Sun Dagger all have in common? A) They were all places used for religious sacrifice. B) They were all built on the orders of ancient Mediterranean kings. C) They all can be used as lunar calendars. D) They were all used by ancient peoples for astronomical observations. E) all of the above
D
What do we mean when we say that the Sun is in gravitational equilibrium? A) The hydrogen gas in the Sun is balanced so that it never rises upward or falls downward. B) The Sun maintains a steady temperature. C) This is another way of stating that the Sun generates energy by nuclear fusion. D) There is a balance within the Sun between the outward push of pressure and the inward pull of gravity. E) The Sun always has the same amount of mass, creating the same gravitational force.
Observations of orbiting stars and gas clouds in galaxies show that they are orbiting extremely massive (tens of millions of solar masses) objects that are invisible.
What evidence do scientists have that supermassive black holes exist?
B
What happened during the accretion phase of the early solar system? A) Atoms and molecules in the gas bonded together and solidified. B) Particles grew by colliding and sticking together. C) The solar nebula differentiated into metals inside of the frost line and ices beyond. D) Large planetesimals captured atmospheres from the solar nebula. E) Earth gained its oceans from icy planetesimal capture.
D
What happens to the rotation of the molecular cloud as it collapses to form a star? A) The rotation rate remains the same and results in stellar rotation B) The rotation rate dissapates and any residual is left in small overall rotation of the star C) The rotation rate increases and results in fast rotation of the star D) the rotation rate increases and results in a disk of material around a protostar E) The rotation rate increases the speed of collapse and produces more massive stars
B
What happens to the visible radiation produced by new stars within a molecular cloud? A) It escapes the cloud completely. B) It is absorbed by dust grains and heats up the cloud. C) It is reflected back onto the protostar, heating it up further. D) The blue light is absorbed and the red light transmitted. E) It shoots out in bright jets.
When the electron falls to a lower orbit, it emits a photon with the difference in energy between the higher and lower orbits.
What happens when an electron moves from a higher energy state or higher orbit to a lower energy state or lower orbit?
A
What is a standard candle? A) an object for which we are likely to know the true luminosity B) an object for which we can easily measure the apparent brightness C) a class of objects in astronomy that all have exactly the same luminosity D) any star for which we know the exact apparent brightness E) a long, tapered candle that lights easily
Comparative planetology is the approach we use to study and understand our solar system. It involves comparing the worlds of our system, including planets, moons, asteroids, and comets, to one another. Its basic premise is that the similarities and differences among the worlds can be traced to common physical processes.
What is comparative planetology?
The process by which gravity separates materials according to density.
What is differentiation in planetary geology?
Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.
What is interstellar reddening?
Surface temperature on the horizontal axis and luminosity on the vertical axis
What is plotted on the axes of a Hertzsprung-Russell diagram?
The process in which molecules go from the solid phase to the gas phase.
What is sublimation?
The Sun's apparent path along the celestial sphere. The Moon and planets all lie near this path too.
What is the ecliptic?
It was likely the combination of an impact crater and a volcanic eruption that changed the global average temperature and trapped debris in the stratosphere to block out the Sun. We have evidence of a giant impact crater in Mexico, and we know the volcano erupted at some point in time.
What is the most likely cause of a mass extinction 65 million years ago? What evidence do we have?
It's a way to describe the balance of the Sun. For instance, if the Sun's core heats up, the Sun is able to self-regulate by expanding and cooling until the internal temperature goes back down. Likewise, if the Sun's core cools, it is able to contract its core to increase the heat and regulate once more.
What is the solar thermostat and how does it work?
C
What makes the North Star, Polaris, special? A) It is the brightest star in the sky. B) It is the star straight overhead. C) It appears very near the north celestial pole. D) It is the star directly on your northern horizon. E) It can be used to determine your longitude on Earth.
D
What makes up the interstellar medium? A) open clusters B) O and B stars C) K and M stars D) gas and dust E) all of the above
D
What mechanism is most responsible for generating the internal heat of Io that drives the volcanic activity? A) accretion B) radioactive decay C) differentiation D) tidal heating E) bombardment
A
What produces the 21-cm line that we use to map out the Milky Way Galaxy? A) atomic hydrogen B) ionized hydrogen C) molecular hydrogen D) carbon monoxide E) helium
The distance from the Sun where temperatures were low enough for hydrogen compounds to condense into ices, between the present-day orbits of Mars and Jupiter
What was the frost line of the solar system?
Copernicus used perfect circles for the orbits of the planets.
When Copernicus first created his Sun-centered model of the universe, it did not lead to substantially better predictions of planetary positions than the Ptolemaic model. Why not?
B
When a rock is held above the ground, we say it has some potential energy. When we let it go, it falls and we say the potential energy is converted to kinetic energy. Finally, the rock hits the ground. What has happened to the energy? A) The energy goes into the ground and, as a result, the orbit of the earth about the Sun is slightly changed. B) The energy goes to producing sound and to heating the ground, rock, and surrounding air. C) The rock keeps the energy inside it (saving it for later use). D) It is lost forever. Energy does not have to be conserved. E) It is transformed back into gravitational potential energy.
A
When an electron in an atom goes from a higher energy state to a lower energy state, the atom A) emits a photon of a specific frequency. B) absorbs a photon of a specific frequency. C) absorbs several photons of a specific frequency. D) can emit a photon of any frequency. E) can absorb a photon of any frequency.
D
When someone on Earth observes the Moon in the first-quarter phase, someone on the Moon facing Earth observes Earth in the A) new Earth phase B) first-quarter Earth phase C) crescent Earth phase D) third-quarter Earth phase E) full Earth phase
E
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 of the region is older than the surface of more heavily cratered regions. E) The surface of the region is younger than the surface in more heavily cratered regions.
C
Where does star formation occur in the Milky Way today? A) in the halo B) in the bulge C) in the spiral arms D) in the Galactic center E) uniformly throughout the galaxy
D
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
E
Which of the following cannot be true of the very first stars formed in the Universe? A) They may have all exploded as supernovae by now. B) They may have formed in large clusters. C) They may have formed singly, in isolation. D) Some may still exist in the Milky Way today. E) They may have had rocky planets around them.
B
Which of the following does NOT lend support to the idea that Pluto is a Kuiper belt object? A) Pluto has a comet-like composition and density. B) Pluto is regarded by many to be a planet. C) Some asteroids have their own moons. D) Pluto has a more eccentric orbit than the other planets. E) Some known Kuiper belt objects are hundreds of kilometers across.
D
Which of the following has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission? A) hydrogen B) oxygen C) silicon D) iron E) uranium
E
Which of the following has your "address" in the correct order? A) You, Earth, solar system, Local Group, local supercluster, Milky Way B) You, Earth, solar system, Milky Way, Local Supercluster, Local group C) You, Earth, solar system, Local Group, Milky Way, Local Supercluster D) You, Earth, Local Group, Local Supercluster, solar system, Milky Way E) You, Earth, solar system, Milky Way, Local Group, Local Supercluster
c
Which of the following is an example in which you are traveling at constant speed but not at constant velocity? A) rolling freely down a hill in a cart, traveling in a straight line B) driving backward at exactly 50 km/hr C) driving around in a circle at exactly 100 km/hr D) jumping up and down, with a period of exactly 60 hops per minute E) none of the above
E
Which of the following is farthest from the Sun? A) Pluto B) Neptune C) an asteroid in the asteroid belt D) a comet in the Kuiper belt E) a comet in the Oort cloud
D
Which of the following is not a characteristic of the inner planets? A) They are relatively smaller than the other planets B) They have solid, rocky surfaces C) Their orbits are relatively closely spaced D) They all have substantial atmospheres E) They have very few, if any, sattelites
C
Which of the following is the largest? A) size of a typical planet B) 1 light-second (light travels 186,000 miles per second) C) 1 AU (average distance from Earth to the Sun D) size of a typical star
D
Which of the following is the origin of almost all the large moons around the jovian planets? A) They are captured asteroids. B) They are captured comets. C) They are captured planets. D) They were formed by condensation and accretion in a disk of gas around the planet. E) They were formed by giant impacts.
A
Which of the following never goes in retrograde motion? A) the Sun B) Venus C) Mars D) Jupiter E) Saturn
E
Which of the following sequences correctly describes the stages of life for a low-mass star? A) red giant, protostar, main-sequence, white dwarf B) white dwarf, main sequence, red giant, protostar C) protostar, red giant, main sequence, white dwarf D) protostar, main sequence, white dwarf, red giant E) protostar, main sequence, red giant, white dwarf
B
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.
A
Which of the following statements about degeneracy pressure is not true? A) Degeneracy pressure varies with the temperature of the star. B) Degeneracy pressure can halt gravitational contraction of a star even when no fusion is occurring in the core. C) Degeneracy pressure keeps any protostar less than 0.08 solar mass from becoming a true, hydrogen-fusing star. D) Degeneracy pressure arises out of the ideas of quantum mechanics. E) Degeneracy pressure supports white dwarfs against gravity.
C
Which of the following statements about novae is not true? A) A star system that undergoes a nova may have another nova sometime in the future. B) A nova involves fusion taking place on the surface of a white dwarf. C) Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now. D) When a star system undergoes a nova, it brightens considerably, but not as much as a star system undergoing a supernova. E) The word nova means "new star" and originally referred to stars that suddenly appeared in the sky, then disappeared again after a few weeks or months.
C
Which of the following statements about scientific models is true? A) A model tries to represent all aspects of nature. B) A model tries to represent only one aspect of nature. C) A model can be used to explain and predict real phenomena. D) All models that explain nature well are correct. E) All current models are correct.
D
Which of the following statements about the celestial sphere is not true? A) When we look in the sky, the stars all appear to be located on the celestial sphere. B) Earth is placed at the center of the celestial sphere. C) The celestial sphere does not exist physically. D) The "celestial sphere" is just another name for our universe. E) From any location on Earth, we can see only half the celestial sphere at any one time.
B
Which of the following statements about the cosmic background radiation is not true? A) It has a temperature of about 3 degrees K above absolute zero. B) It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. C) It had a much higher temperature in the past. D) It was discovered by Penzias and Wilson in the early 1960s. E) It appears essentially the same in all directions (it is isotropic).
A
Which of the following statements is not an observed pattern of motion in our solar system? A) Most planets orbit at the same speed. B) All planets orbit the Sun in the same direction. C) Most planetary orbits lie nearly in the same plane. D) Most planets rotate in the same direction in which they orbit. E) Almost all moons orbit their planet in the same direction as the planet's rotation..
E
Which planet has a ring system? A) Jupiter B) Saturn C) Uranus D) Neptune E) all of the above
c
Which planet has the highest average surface temperature, and why? A) Mercury, because it is closest to the Sun B) Mercury, because of its dense carbon dioxide atmosphere C) Venus, because of its dense carbon dioxide atmosphere D) Mars, because of its red color E) Jupiter, because it is so big
D
Why are neutrinos so difficult to detect? A) because they are so rare B) because they have no mass C) because they move nearly at the speed of light D) because they rarely interact with matter E) because they are so small
C
Why are there no impact craters on the surface of Io? A) It is too small to have been bombarded by planetesimals in the early solar system. B) Jupiter's strong gravity attracted the planetesimals more strongly than Io and thus none landed on its surface. C) Io did have impact craters but they have all been buried in lava flows. D) Any craters that existed have been eroded through the strong winds on Io's surface. E) Io's thick atmosphere obscures the view of the craters.
B
Why did the solar nebula heat up as it collapsed? A) Nuclear fusion occurring in the core of the protosun produced energy that heated the nebula. B) As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy. C) Radiation from other nearby stars that had formed earlier heated the nebula. D) The shock wave from a nearby supernova heated the gas. E) Collisions among planetesimals generated friction and heat.
A
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.
When a comet passes through Jupiter's orbit, a piece of gas or dust will fall from the coma, creating dust or gas tails.
Why do comets have tails?
The differences can arise from conditions in their protogalactic cloud and from collisions with other galaxies. Slowly rotating or high-density protogalactic clouds may form elliptical rather than spiral galaxies. Ellipticals may also form through the collision and merger of two spiral galaxies.
Why do galaxies differ?
C
Why do jovian planets bulge around the equator and have a squashed appearance? A) They are much more massive than terrestrial planets. B) Their large systems of moons and rings gravitationally attract the mass around the equator more. C) Their rapid rotation flings the mass near the equator outward. D) Their internal heat sources exert a pressure against the sides of the planets. E) All of the above.
C
Why do we call dark matter "dark"? A) It emits no visible light. B) We cannot detect the type of radiation that it emits. C) It emits no or very little radiation of any wavelength. D) It blocks out the light of stars in a galaxy.
A
Why do we have seasons on Earth? A) As Earth goes around the Sun and Earth's axis remains pointed toward Polaris, the Northern and Southern hemispheres alternatively receive more and less direct sunlight. B) The tilt of Earth's axis constantly changes between 0 and 23.5 degrees, giving us summer when Earth is tilted more and winter when it is straight up. C) Earth's distance from the Sun varies, so it is Summer when we are closer to the Sun and winter when we are farther from the Sun. D) Seasons are caused by the influence of the planet Jupiter on our orbit.
The Universe was so small and hot during the early phases of the Big Bang that there was spontaneous particle creation from energy and annihilation. We can recreate the conditions of particle creation and annihilation at high energies using particle accelerators and thereby test theories of the Big Bang. Furthermore, we cannot actually see these early stages directly because the Universe is so dense that it is opaque.
Why do we test theories about the Big Bang using particle accelerators instead of just using bigger and bigger telescopes to look further back in time?
As it gains density, it also gains gravitational equilibrium because gravitational potential energy converts to thermal energy, which creates thermal pressure to work against the crush of gravity that causes the collapse in the first place. As the thermal pressure increases, the density increases, and nothing can escape.
Why does a cloud collapse rapidly at first and then slow down as it gets denser?
Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.
Why does a star grow larger after it exhausts its core hydrogen?
The gravity is able to compress the core even more, which makes the radius smaller, despite the extremely high density.
Why does the size of a white dwarf decrease with increasing mass?
B
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) It is unknown why this is so.
Compared to how far stars are from us, their planets orbits are very small. Further, planets only reflect light (or weakly emit infrared radiation) and are therefore much (billions) of times fainter than the star. It is very difficult to make an image of such a faint object so close to such a bright object.
Why is it so difficult to make a direct image of a planet around another star?
The difference is that the comets in the Kuiper belt have not been scattered out by gravitational interactions with giant planets. Kuiper-belt comets formed beyond the orbit of Neptune in the flattened solar nebula and their orbits have not been greatly changed. Oort-cloud comets, however, formed within the orbit of the jovian planets and have been scattered out (or impacted other bodies in the solar system). The scattering was random so the orbits are in every direction and inclination, resulting in a spherical Oort cloud.
Why is the Kuiper belt flat but the Oort cloud spherical?
B
Why of the following types of galaxies are found in large clusters? A) spirals B) ellipticals C) lenticulars D) irregulars
C
Why should galaxy collisions have been more common in the past than they are today? A) Galaxies were more active in the past and therefore would have collided with each other more frequently. B) Galaxies were much bigger in the past since they had not contracted completely. C) Galaxies were closer together in the past because the universe was smaller. D) Galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars and light. E) Galaxy collisions shouldn't have been more common in the past than they are now.
Both events need to have a companion star, but our Sun isn't in a binary system.
Why won't our Sun ever undergo a nova or a white dwarf supernova event?
The Sun's gravitational pull would remain unchanged because it would still have the same amount of mass, even though its area would decrease.
Why would Earth's orbit be unaffected were the Sun to suddenly become a black hole?
Although Titan contains liquid methane and ethane, we wouldn't see liquid water because it would be frozen due to Titan's extremely far distance from the Sun.
Would we expect to see liquid water rainfall on Saturn's moon Titan? Why or why not?
As the temperature rises, the ice will melt into liquid water. It soon evaporates into a gas. As the heat increases even more, the energy in the gas increases as well, and it eventually ionizes the gas and turns it into a plasma.
You have a chunk of water ice. Describe what happens to it, in terms of phases, as you raise the temperature to millions of degrees.
