AST1002 final

In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe? A. By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur. B. Temperatures in the early universe were never above the roughly 100 million Kelvin required for helium fusion. C. Helium fusion occurred, but the carbon nuclei that were made were later destroyed by the intense radiation in the early universe. D. No one knows - this is one of the major mysteries in astronomy.

A. By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur.

Which of the following statements about large-scale structure is probably not true? A. Clusters and superclusters appear to be randomly scattered about the universe, like dots sprinkled randomly on a wall. B. Voids between superclusters began their existence as regions in the universe with a slightly lower density than the rest of the universe. C. Many cluster and superclusters are still in the process of formation as their gravity gradually pulls in new members. D. Galaxies and clusters have grown around tiny density enhancements that were present in the early universe.

A. Clusters and superclusters appear to be randomly scattered about the universe, like dots sprinkled randomly on a wall. Clusters and superclusters seem to lie on great chains and sheets, suggesting they fall along a "framework" that was determined in the very early universe.

Which of the following statements about degeneracy pressure is not true? A. Degeneracy pressure can arise only from interactions among electrons. B. Degeneracy pressure arises from a quantum mechanical effect that we don't notice in our daily lives. C. Black holes form when gravity overcomes neutron degeneracy pressure. D. Degeneracy pressure can continue to support an object against gravitational collapse even if the object becomes extremely cold.

A. Degeneracy pressure can arise only from interactions among electrons.

Each of the following lists two facts. Which pair of facts can be used with Newton's version of Kepler's third law to determine the mass of the Sun? A. Earth is 150 million km from the Sun and orbits the Sun in one year. B. Earth rotates in one day and orbits the Sun in one year. C. Mercury is 0.387 AU from the Sun and Earth is 1 AU from the Sun. D. The mass of Earth is 6 x 1024 kg and Earth orbits the Sun in one year.

A. Earth is 150 million km from the Sun and orbits the Sun in one year. A single planet's orbital distance and orbital period are all we need to determine the Sun's mass Newton's version of Kepler's third law.

Suppose that Jupiter had never existed, and there was no planet in our solar system between Mars and Saturn. How would we expect this to have affected Earth? A. Earth would have been hit by many more comet impacts. B. There would not have been any effect, since Jupiter is in the outer solar system and Earth is in the inner solar system. C. Earth's orbit would have been unstable, and our planet would have spiraled into the Sun. D. There would be no water on Earth.

A. Earth would have been hit by many more comet impacts.

How do the speeds at which we are moving with Earth's rotation and orbit compare to the speeds of more familiar objects? A. Earth's rotation carries most people around the axis faster than a commercial jet travels, and Earth's orbit carries us around the Sun faster than the Space Shuttle orbits Earth. B. Earth's rotation carries most people around the axis at about the speed of a car on the freeway, and Earth's orbit carries us around the Sun at about the speed of a commercial jet. C. Earth's rotation carries most people around the axis at about the speed at which the Space Shuttle orbits Earth, and Earth's orbit carries us around the Sun at nearly the speed of light. D. Earth's rotation carries most people around the axis at about the speed of a commercial jet, and Earth's orbit carries us around the Sun at about the speed of a military jet.

A. Earth's rotation carries most people around the axis faster than a commercial jet travels, and Earth's orbit carries us around the Sun faster than the Space Shuttle orbits Earth.

If the Sun suddenly stopped emitting neutrinos, what might we infer (after checking that our neutrino detectors were still operational)? A. Fusion reactions in the Sun have ceased within the past few minutes. B. Fusion reactions in the Sun ceased a few hundred thousand years ago. C. The Sun has exhausted its supply of neutrinos. D. Fission reactions in the Sun have ceased.

A. Fusion reactions in the Sun have ceased within the past few minutes.

Which statement concerning black hole masses and Schwarzschild radii is not true? A. In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the companion star. B. For black holes produced in massive star supernovae, Schwarzschild radii are typically a few to a few tens of kilometers. C. Even an object as small as you could become a black hole if there were some way to compress you to a size smaller than your Schwarzschild radius. D. The more massive the black hole, the larger the Schwarzschild radius.

A. In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the companion star. The Schwarzschild radius is a property of the black hole itself and does not depend on whether the black hole has a companion object.

How does the idea of inflation account for the existence of the "seeds" of density from which galaxies and other large structures formed? A. Inflation would have caused random, microscopic quantum fluctuations to grow so large in size that they became the seeds of structure. B. Inflation predicts that gravity would have been very strong and thereby would have concentrated mass into seeds. C. Inflation predicts that temperatures and densities should have become nearly equal throughout the universe. D. Inflation tells us that the universe should have a "flat" overall geometry, and this led to the flat disks of galaxies.

A. Inflation would have caused random, microscopic quantum fluctuations to grow so large in size that they became the seeds of structure.

Why do we call dark matter "dark"? A. It emits no radiation that we have been able to detect. B. It blocks out the light of stars in a galaxy. C. It contains large amounts of dark-colored dust. D. It is dark brown or dark red in color.

A. It emits no radiation that we have been able to detect.

Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes? A. It is closer to the stars. B. Stars do not twinkle when observed from space. C. It never has to close because of cloudy skies. D. It can observe infrared and ultraviolet light, as well as visible light.

A. It is closer to the stars. Distance to the stars has absolutely nothing to do with it, as should be apparent if you consider the scale of the solar system and the distances to stars to scale (as discussed in Chapter 1)

Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different? A. It would have only one tail instead of two. B. It would not have a coma. C. It would be much brighter in appearance. D. It would not have a nucleus.

A. It would have only one tail instead of two.

Which of the following best describes the current status of the evidence concerning whether life has ever existed on Mars? A. Mars probably once had a habitable surface, but we do not know if it had life. B. Clear evidence strongly suggests that life once existed on Mars. C. While current evidence is mixed, ongoing studies should ensure that we will have a definitive answer to the question of whether life ever existed on Mars within about five years. D. Clear evidence indicates that Mars never had conditions favorable to life.

A. Mars probably once had a habitable surface, but we do not know if it had life. Strong evidence exists for past water on the Martian surface, suggesting that life would have been possible. However, there is not yet any actual evidence that life existed.

Using the ideas discussed in your textbook, in what sense are we "star stuff"? A. Nearly every atom from which we are made was once inside of a star. B. The overall chemical composition of our bodies is about the same as that of stars. C. We could not survive without light from our star, the Sun. D. Movie stars and other people are all made of the same stuff, so we all have the potential to be famous.

A. Nearly every atom from which we are made was once inside of a star.

Suppose that large jovian planets had never formed in our solar system. Which of the following would most likely be true? A. Neither the asteroid belt nor Oort cloud would exist. B. Earth would orbit much closer to the Sun. C. Earth would have suffered far fewer impacts. D. There would be a large empty region in our solar system between the orbit of Mars and the Kuiper belt.

A. Neither the asteroid belt nor Oort cloud would exist.

Why won't Pluto collide with Neptune? A. Pluto orbits the Sun exactly two times for every three Neptune orbits, which ensures they never come close together. B. Pluto is always much farther from the Sun than Neptune. C. Actually, a collision of the two is inevitable within the next billion years. D. Pluto's orbit never comes anywhere close to Neptune's orbit.

A. Pluto orbits the Sun exactly two times for every three Neptune orbits, which ensures they never come close together.

The choices below describe four hypothetical planets. Which one would you expect to have the hottest interior? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) A. Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months. B. Size: same as Mars. Distance from Sun: same as Earth. Rotation rate: once every 18 hours. C. Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days. D. Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours.

A. Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months. Largest size means the highest interior temperature.

Which of the following is not true about differences between novae and supernovae? A. Supernovae eject gas into space but novae do not. B. Novae occur only in binary star systems, while supernovae can occur both among single stars and among binary star systems. C. The same star can undergo novae explosions more than once, but can undergo only a single supernova. D. Novae are much less luminous than supernovae.

A. Supernovae eject gas into space but novae do not.

What is the best way to determine a galaxy's redshift? A. Take a spectrum of the galaxy, and measure the difference in wavelength of spectral lines from the wavelengths of those same lines as measured in the laboratory. B. Find the galaxy's apparent distance, and look up the redshift based on Hubble's Law. C. Find the color of the galaxy, and estimate its distance based on how red the galaxy is. D. Measure the magnitude of the galaxy, estimate its distance, and calculate its redshift using Hubble's Law.

A. Take a spectrum of the galaxy, and measure the difference in wavelength of spectral lines from the wavelengths of those same lines as measured in the laboratory. Even if the redshift is cosmological, we still measure it just like a Doppler shift.

Which of the following best explains why the Moon's orbital period and rotation period are the same? A. The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period. B. The law of conservation of angular momentum ensured that the Moon must have the same amount of rotational angular momentum as it has of orbital angular momentum. C. The equality of the Moon's orbital and rotation periods is an extraordinary astronomical coincidence. D. The Moon was once closer to Earth, but the force of gravity got weaker as the Moon moved farther away.

A. The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period.

How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf? A. The accretion disk around a neutron star is much hotter and emits higher-energy radiation. B. The accretion disk around a neutron star is made mostly of helium while the accretion disk around a white dwarf is made mostly of hydrogen. C. The accretion disk around a neutron star always contains much more mass. D. The accretion disk around a neutron star is more likely to give birth to planets.

A. The accretion disk around a neutron star is much hotter and emits higher-energy radiation. This is true because of the much stronger gravity near the surface of the neutron star.

Suppose that a lone asteroid happens to be passing Jupiter on an unbound orbit (well above Jupiter's atmosphere and far from all of Jupiter's moons.) Which of the following statements would be true? A. The asteroid's orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on. B. There is no way to predict what would happen. C. Jupiter's gravity would capture the asteroid, making it a new moon of Jupiter. D. Jupiter's gravity would suck in the asteroid, causing it to crash into Jupiter.

A. The asteroid's orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on.

What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old? A. The basic chemical composition of the universe had been determined. B. It marks the time at which the first stars formed. C. It marks the time at which the expansion of the universe had settled down to its current rate. D. The proportions of dark matter and luminous matter had been determined.

A. The basic chemical composition of the universe had been determined. After this point, the density and temperature were too low to allow for any more fusion, so no new elements could be created (until stars began to do fusion much later on, but fusion in stars has changed the overall chemical composition only by about 2%).

The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is most likely to be located in the halo of our galaxy? A. The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs. B. The diagram shows no main-sequence stars at all, but it has numerous supergiants and white dwarfs. C. The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants. D. The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and supergiants.

A. The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs. This is an old cluster so it must be a globular cluster, and most globular clusters are in the halo of the galaxy.

Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies? A. The fact that spiral galaxies have both disk and halo components B. Starbursts C. The presence of very large, central dominant galaxies in clusters of galaxies D. The fact that elliptical galaxies are more common in clusters of galaxies than outside clusters

A. The fact that spiral galaxies have both disk and halo components This can be explained by the basic galaxy formation process, and does not require any interaction with other galaxies.

Which of the following is not considered a potential solution to the question of why we lack any evidence of a galactic civilization? A. The galactic civilization probably is undetectable because they operate under different laws of physics from the ones we know. B. There is no galactic civilization because we are the first species ever to achieve the ability to study the universe. C. The galactic civilization is deliberately avoiding contact with us. D. There is no galactic civilization because all civilizations destroy themselves before they achieve the ability to colonize the galaxy.

A. The galactic civilization probably is undetectable because they operate under different laws of physics from the ones we know. We expect that the laws of physics are the same everywhere.

Imagine that it turns out that dark matter (not dark energy) is made up of an unstable form of matter and that all of it suddenly decays tomorrow into photons or other forms of energy. Based on current understanding, which of the following would begin to occur? A. The galaxies in clusters would begin to fly apart. B. Planetary systems would begin to expand and disperse. C. Stars would begin to stop having nuclear fusion in their cores. D. The expansion of the universe would begin coming to a halt.

A. The galaxies in clusters would begin to fly apart. Dark matter provides most of the gravity that binds galaxies into clusters of galaxies. So without dark matter, the galaxies would fly apart.

Many scientists suspect that Venus has a stronger and thicker lithosphere than Earth. If this is true, which of the following could explain it? A. The high surface temperature that has "baked out" all the liquid water from Venus's crust and mantle B. The slow rotation of Venus C. The smaller size of Venus, which has allowed it to lose much more internal heat than Earth D. The apparent lack of plate tectonics on Venus

A. The high surface temperature that has "baked out" all the liquid water from Venus's crust and mantle

According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size? A. The law of conservation of angular momentum B. The law of universal gravitation C. The law of conservation of energy D. Einstein's law E = mc 2

A. The law of conservation of angular momentum

According to our theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size? A. The law of conservation of energy B. Newton's third law C. The law of conservation of angular momentum D. The two laws of thermal radiation

A. The law of conservation of energy As it shrank in size, gas particles lost gravitational potential energy. Since energy must be conserved, this energy became thermal energy.

All of the following observations are real. Which one does not support the model in which active galactic nuclei are powered by accretion disks around massive black holes? A. The most luminous active galactic nuclei have huge redshifts. B. The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun. C. X-ray emission from active galactic nuclei can vary significantly in times as short as a few days. D. Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed.

A. The most luminous active galactic nuclei have huge redshifts. The redshifts are a consequence of being at great distance from us in an expanding universe, and do not directly tell us anything about why the objects are so luminous.

Which of the following general statements about Earth's atmosphere is not true? A. The nitrogen and oxygen in Earth's atmosphere keep the surface pleasantly warm. B. Without the relatively rare gas called ozone, Earth's surface would be bathed in dangerous ultraviolet light from the Sun. C. The oxygen in our atmosphere was released by living organisms. D. Gas high in the atmosphere absorbs dangerous X rays from the Sun.

A. The nitrogen and oxygen in Earth's atmosphere keep the surface pleasantly warm.

What evidence suggests that most of the mass of the Milky Way is in the form of dark matter? A. The orbital speeds of stars far from the galactic center are surprisingly high. B. Our view of distant galaxies is often obscured by dark blotches, which are presumably made of dark matter. C. Although dark matter emits no visible light, we have detected its radio emissions. D. Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk.

A. The orbital speeds of stars far from the galactic center are surprisingly high. This suggests that these stars are feeling gravitational effects from unseen matter in the halo.

According to current understanding, which of the following is required in order for a planet to have rings? A. The planet must have many small moons that orbit relatively close to the planet in its equatorial plane. B. The planet must orbit its star at a distance greater than Mars orbits the Sun. C. The planet must once have had a large moon that came too close to it, shattering the moon and creating the ring particles. D. The planet must be at least as massive as Saturn.

A. The planet must have many small moons that orbit relatively close to the planet in its equatorial plane. Ring particles come from small and large impacts on these small moons.

Why is the radiation so intense in the region that traces Io's orbit around Jupiter (the Io torus)? A. The region is full of gases that become ionized after they are released from volcanoes on Io. B. Io's gravity allows this region to capture huge numbers of charged particles from the solar wind. C. An orbital resonance between Io, Europa, and Ganymede makes the radiation intense. D. Jupiter's strong magnetic field makes the radiation intense everywhere, and the region around Io is no different than any other region.

A. The region is full of gases that become ionized after they are released from volcanoes on Io. Io's low gravity allows these gases to escape.

Suppose you find a rock that contains 10 micrograms of radioactive potassium-40, which has a half-life of 1.25 billion years. By measuring the amount of its decay product (argon-40) present in the rock, you conclude that there must have been 80 micrograms of potassium-40 when the rock solidified. How old is the rock? A. 2.5 billion years B. 3.75 billion years C. 5.0 billion years D. 1.25 billion years

B. 3.75 billion years The current 10 micrograms of potassium-40 is 1/8 of the original 80 grams, which means the amount of potassium-40 has declined by a factor of 8. Therefore, three half-lives have passed (since 23 = 8) and the rock is 3 × 1.25 = 3.75 billion years old.

Which of the following best describes a set of conditions under which archaeoastronomers would conclude that an ancient structure was used for astronomical purposes? A. The structure has numerous features indicating alignments with movements of the Sun and cultural heritage claimed that the rulers were descendants of the Sun. B. The structure has the same dome shape as modern astronomical observatories. C. They find that, looking out from the center of the building, there are two windows that align with the rise and set points of two bright stars. D. The structure consists of lines in the desert that make patterns visible only from high above.

A. The structure has numerous features indicating alignments with movements of the Sun and cultural heritage claimed that the rulers were descendants of the Sun.

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

A. The sudden collapse of an iron core into a compact ball of neutrons

According to our present theory of solar system formation, how did Earth end up with enough water to make oceans? A. The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars. B. Earth formed at a distance from the Sun at which liquid water happened to be plentiful in the solar nebula. C. The water was brought to the forming Earth by planetesimals that accreted near Earth's orbit. D. The water was formed by chemical reactions among the minerals in the Earth's core.

A. The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars.

Which of the following best describes why scientists seek to identify even very small asteroids that could potentially hit Earth? A. To try to prevent an impact that might destroy a town or city. B. To help us understand the origin of the solar system. C. To allow us to capture the asteroids and use them for their resources. D. To try to prevent an impact that might cause the extinction of the human race.

A. To try to prevent an impact that might destroy a town or city.

All the following statements about Venus are true. Which one offers evidence of a global repaving about a billion years ago? A. Venus has relatively few impact craters and these craters are distributed fairly evenly over the entire planet. B. Venus has many circular features, called coronae, which appear to be tectonic in origin. C. Venus's largest features are three elevated regions that look somewhat like continents. D. Venus appears to lack any water that could lubricate the flow of rock in its crust and mantle.

A. Venus has relatively few impact craters and these craters are distributed fairly evenly over the entire planet.

The Sun's surface seethes and churns with a bubbling pattern. Why? A. We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface. B. The churning is an illusion created by varying radiation, as the gas on the Sun's surface is actually quite still. C. The Sun's surface is boiling. D. The churning gas is being stirred up by the strong solar wind.

A. We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface.

Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation? A. We can learn the distance to the galaxy. B. Under the rules of the International Astronomical Union, we will be entitled to naming rights for the galaxy. C. It will allow us to determine the mass of the galaxy. D. It will allow us to calculate the rotation rate of the galaxy.

A. We can learn the distance to the galaxy. We will be able to use the Cepheid's period to determine its luminosity from the period-luminosity relation. Then we can calculate its distance by comparing its luminosity and its apparent brightness in our sky, using the inverse square law for light. This tells us the Cepheid's approximate distance, which is also approximate distance to its host galaxy.

Imagine for a moment that despite all the evidence, Earth actually is not rotating and orbiting the Sun. Which of these hypothetical observations (none of them are real) would be inconsistent with our Sun-centered view of the solar system? A. We discover a small planet beyond Saturn that rises in the west and sets in the east each day. B. We discover that the universe is actually contracting, not expanding. C. We discover an Earth-sized planet orbiting the Sun beyond the orbit of Pluto. D. We find that we are unable to measure any parallax for a distant galaxy.

A. We discover a small planet beyond Saturn that rises in the west and sets in the east each day.

Which of the following is not key evidence in support of the idea that all life today shares a common ancestor? A. We have identified fossils of the first life forms that ever existed on Earth. B. All life uses DNA and the same genetic code. C. All life builds proteins from the same amino acids and uses ATP to store energy in cells. D. Mapping of gene sequences shows how life is all related.

A. We have identified fossils of the first life forms that ever existed on Earth. The first life forms probably did not leave any fossils behind, and even if they did, we certainly haven't yet found them.

Why are white dwarf supernovae more useful than massive star supernovae for measuring cosmic distances? A. White dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak luminosities. B. White dwarf supernovae follow a period-luminosity relation, while massive supernovae do not. C. We can see only white dwarf supernovae in distant galaxies, not massive star supernovae. D. White dwarf supernovae are much more common than massive star supernovae.

A. White dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak luminosities. This allows white dwarf supernovae to be used as standard candles, since we can assume we know their true luminosities.

Which of the following statements about X rays and radio waves is not true? A. X rays travel through space faster than radio waves. B. X rays have shorter wavelengths than radio waves. C. X rays and radio waves are both forms of light, or electromagnetic radiation. D. X rays have higher frequency than radio waves.

A. X rays travel through space faster than radio waves. All light travels at the same speed, so radio waves and X rays travel at the same speed.

The reason that small planets tend to lose interior heat faster than larger planets is essentially the same as the reason that __________. A. a large baked potato takes longer to cool than a small baked potato B. thunderstorms tend to form on hot summer days C. gas bubbles form and rise upward in boiling water D. Earth contains more metal than the Moon

A. a large baked potato takes longer to cool than a small baked potato

Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is __________. A. converted to an amount of energy equal to 4 million tons times the speed of light squared B. ejected into space in a solar wind C. reabsorbed as molecular hydrogen D. ejected into space by solar flares

A. converted to an amount of energy equal to 4 million tons times the speed of light squared

A star with a parallax angle of 1/20 arcsecond is __________. A. 20 parsecs away B. 1/20 parsec away C. 10 parsecs away D. 20 light-years away

A. 20 parsecs away This is true because distance in parsecs = 1/(parallax angle in arcsecond). Note that 20 parsecs is equivalent to 20 × 3.26 = 65.2 light-years.

Which of the following statements about thermal radiation is always true? A. A hot object emits more radiation per unit surface area than a cool object. B. A cold object produces more total infrared and radio emission per unit surface area than a hot object. C. A hot object produces more total infrared emission than a cooler object. D. All the light emitted by hot object has higher energy than the light emitted by a cooler object.

A. A hot object emits more radiation per unit surface area than a cool object.

According to Kepler's third law (p 2 = a 3), how does a planet's mass affect its orbit around the Sun? A. A planet's mass has no effect on its orbit around the Sun. B. More massive planets must have more circular orbits. C. More massive planets orbit the Sun at higher average speed. D. A more massive planet must have a larger semimajor axis.

A. A planet's mass has no effect on its orbit around the Sun. Kepler's third law makes no allowance for planetary mass, and in fact the planet's mass has virtually no effect on its orbit of the Sun. (The Sun's mass has a major effect, however.)

The most basic difference between elliptical galaxies and spiral galaxies is that __________. A. elliptical galaxies lack anything resembling the disk of a spiral galaxy B. elliptical galaxies have a spheroidal component (of stars distributed spherically about the galactic center), and spiral galaxies do not C. elliptical galaxies are very old and spiral galaxies are very young D. elliptical galaxies lack anything resembling the halo of a spiral galaxy

A. elliptical galaxies lack anything resembling the disk of a spiral galaxy In essence, elliptical galaxies are "all bulge and halo" with no disk, while spiral galaxies have a disk as well as a bulge and halo.

Which of the following best describes how the greenhouse effect works? A. A planet's surface absorbs visible sunlight and returns this absorbed energy to space as infrared light. Greenhouse gases slow the escape of this infrared radiation, which thereby heats the lower atmosphere. B. Greenhouse gases absorb X rays and ultraviolet light from the Sun, and this absorbed radiation then heats the atmosphere and the surface. C. The greenhouse effect is caused primarily by ozone, which absorbs ultraviolet light and thereby makes the atmosphere much hotter than it would be otherwise. D. Greenhouse gases absorb infrared light coming from the Sun, and this absorbed sunlight heats the lower atmosphere and the surface.

A. A planet's surface absorbs visible sunlight and returns this absorbed energy to space as infrared light. Greenhouse gases slow the escape of this infrared radiation, which thereby heats the lower atmosphere.

We are not yet capable of detecting life on planets around other stars. But as our technology develops, our first real chance of detecting such life will probably come from __________. A. examining high-resolution images of the planets made by orbiting telescopes B. examining spectral lines from the atmospheres of distant planets C. determining the orbital properties of the planets D. sending spacecraft to study the planets up close

A. examining high-resolution images of the planets made by orbiting telescopes Certain spectral signatures may lead us to conclude that life is present.

Over time, the star-gas-star cycle leads the gas in the Milky Way to _________. A. have a greater abundance of heavy elements B. have a lower abundance of heavy elements C. become denser and have a greater abundance of heavy elements D. become denser and hotter

A. have a greater abundance of heavy elements With every cycle, new stars have died and produced heavy elements that are recycled into space.

Suppose a planet is discovered by the Doppler method and is then discovered to have transits. In that case, we can determine all the following about the planet except __________. A. its rotation period B. its orbital period C. its precise mass D. its physical size (radius) E. its density

A. its rotation period We do not get any direct information about rotation period. (However, if the planet is very close to its star, we can sometimes conclude that it has synchronous rotation, in which case the rotation period and orbital period are the same.)

Suppose you use the Southern Cross to determine that the south celestial pole appears 40 degrees above your horizon. Then you must be located at _________. A. latitude 40 degrees south B. latitude 40 degrees north C. longitude 40 degrees D. latitude 50 degrees south

A. latitude 40 degrees south The altitude of the south celestial pole is equal to your latitude; because you see the south celestial pole at altitude 40 degrees, you must be located at latitude 40 degrees south.

You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star's __________. A. mass B. apparent brightness C. distance D. spectral type

A. mass

The cores of the terrestrial worlds are made mostly of metal because __________. A. metals sunk to the centers a long time ago when the interiors were molten throughout B. over billions of years, convection gradually brought dense metals downward to the core C. the core contained lots of radioactive elements that decayed into metals D. the terrestrial worlds as a whole are made mostly of metal

A. metals sunk to the centers a long time ago when the interiors were molten throughout This sinking was part of the process called differentiation.

A net force acting on an object will always cause a change in the object's _____. A. momentum B. mass C. direction D. speed

A. momentum

Which two factors are critical to the existence of the carbon dioxide (CO2) cycle on Earth? A. plate tectonics and liquid water oceans B. life and atmospheric oxygen C. life and active volcanism D. active volcanism and active tectonics

A. plate tectonics and liquid water oceans Carbon dioxide dissolves in the oceans and becomes incorporated into carbonate rock; plate tectonics recycles the carbonate rock into the mantle, where it melts and releases its gas back to the atmosphere.

In the Drake equation (Number of Civilizations = N HP × f life × f civ × f now), we expect the term f civ to be small if _______. A. primitive life is common but intelligent life is rare B. most civilizations destroy themselves within just a few hundred years of arising C. most habitable planets never actually get life on them D. most of the civilizations that have ever existed are still out and about in the galaxy

A. primitive life is common but intelligent life is rare The first two terms (N HP × f life) tell us the number of habitable planets with life of some kind. The term f civ then tells us the fraction of these planets on which the life eventually leads to an intelligent civilization. So if intelligence is rare, than civilizations would also be rare, making f civ small.

Which of the following observatories is most likely to discover a black hole in a binary system? A. the Chandra X-Ray Observatory B. the Arecibo Radio Observatory C. the Hubble Space Telescope D. the SOFIA airborne infrared observatory

A. the Chandra X-Ray Observatory Accretion disks around black holes (and neutron stars) emit X rays.

Suppose you want to observe and study the radiation from gas inside an interstellar bubble created by a supernova. Which of the following observatories will be most useful? A. the Chandra X-ray Observatory B. the SOFIA airborne infrared observatory C. the Hubble Space Telescope D. the Keck I telescope on the summit of Mauna Kea

A. the Chandra X-ray Observatory The gas is very hot and glows in X rays.

Applying the Newton's version of Kepler's third law (or the orbital velocity formula) to the a star orbiting 40,000 light-years from the center of the Milky Way galaxy allows us to determine ______. A. the mass of the Milky Way Galaxy that lies within 40,000 light-years of the galactic center B. the total mass of the entire Milky Way Galaxy C. the mass of the black hole thought to reside in the center of the galaxy D. the percentage of the galaxy's mass that is made of dark matter

A. the mass of the Milky Way Galaxy that lies within 40,000 light-years of the galactic center Note that this method tells us only the mass within that orbit, not the total mass of the entire galaxy.

Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole. The black hole is surrounded by an accretion disk. Sometime within the next million years or so, the civilization's planet is likely to be doomed because ________. A. the red giant will probably supernova within the next million years B. jets of material shot out of the accretion disk will shoot down their planet C. the red giant star, which provides most of energy the civilization needs to exist, will soon be destroyed in the accretion disk D. the planet's orbit gradually will decay, as it is sucked in by the black hole E. tidal forces from the black hole will rip the planet apart

A. the red giant will probably supernova within the next million years

In science fiction movies, spaceships are often shown dodging through large numbers of closely spaced, boulder-size objects. Which of the following real things in our solar system would look most like such science fiction dangers? A. the rings of Saturn B. the Oort cloud C. the asteroid belt D. the atmosphere of Jupiter

A. the rings of Saturn

Which of the following statements correctly describes current understanding of the eventual fate of the universe? A. Although the accelerating expansion suggests that the universe will continue to expand forever, it is possible that future discoveries will indicate a different fate. B. The universe will gradually decay as it continues to expand, with protons eventually decaying and black holes ultimately evaporating, leaving the universe cold and dark. C. The universe will continue to expand forever, because only gravity could reverse the expansion, and it is not strong enough to do so. D. The acceleration of the expansion will eventually lead to a Big Rip that will break all matter apart.

A. Although the accelerating expansion suggests that the universe will continue to expand forever, it is possible that future discoveries will indicate a different fate. Remember, forever is a very long time, and we may learn much more about the universe in the future, possibly including things that will change our understanding of the eventual fate of the universe.

The Sun's path, as viewed from the equator, is highest in the sky on __________. A. the spring and fall equinoxes B. the summer solstice C. the day when Earth is closest to the Sun D. the winter solstice

A. the spring and fall equinoxes At the equator, the Sun passes through the zenith just twice each year: at noon on the spring and fall equinoxes.

According to our basic scenario of solar system formation, why do the jovian planets have numerous large moons? A. As the growing jovian planets captured gas from the solar nebula, the gas formed swirling disks around them, and moons formed from condensation accretion within these disks. B. 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. C. The many moons of the jovian planets remains one of the unexplained mysteries of the formation of our solar system. 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.

A. As the growing jovian planets captured gas from the solar nebula, the gas formed swirling disks around them, and moons formed from condensation accretion within these disks. That is, the formation of large moons around jovian planets was much like a smaller version of the formation of planets around the Sun.

At which lunar phase(s) are tides most pronounced (for example, the highest high tides)? A. Both new and full moons B. Both first and third quarters C. Third quarter moon only D. New moon only E. Full moon only

A. Both new and full moons These are the spring tides, when the tidal forces of the Sun and Moon work together.

Based on the definition of apparent brightness, which units are appropriate for its measurement? A. watts per square meter B. joules C. watts D. newtons

A. watts per square meter Apparent brightness is defined as the power of starlight reaching us per unit area. Power has units of watts and area has units of square meters.

Suppose you drop a 10-pound weight and a 5-pound weight on the Moon, both from the same height at the same time. What will happen? A. Both will hit the ground at the same time. B. The 10-pound weight will hit the ground before the 5-pound weight. C. The 5-pound weight will hit the ground before the 10-pound weight. D. Both weights will float freely, since everything is weightless on the Moon.

A. Both will hit the ground at the same time. The acceleration of gravity on the Moon is smaller than it is on Earth, but it still is the same for all objects. Therefore both objects will fall at the same rate. (And because there is no air on the Moon, they'll hit at the same time no matter what shape or density they have.)

We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs. But if they do, then which of the following would be true? A. Brown dwarfs would outnumber all ordinary stars. B. Brown dwarfs would be extremely rare. C. Brown dwarfs would be responsible for most of the overall luminosity of our Milky Way Galaxy. D. Most of the brown dwarfs in the Milky Way Galaxy would be quite young in age.

A. Brown dwarfs would outnumber all ordinary stars. Less massive stars are more common than more massive stars, so if this trend continues then the very low mass brown dwarfs would be more common than any type of main-sequence star.

How did astronomers discover the relationship between spectral type and mass for main sequence stars? A. By measuring the masses and spectral types of main-sequence stars in binary systems. B. By using computer models of hydrogen fusion and stellar structure. C. By comparing stars with the same spectral type but different luminosities. D. By measuring stellar radii with very powerful telescopes.

A. By measuring the masses and spectral types of main-sequence stars in binary systems. We can only measure mass directly for stars in binary systems, so this is how the relationship was first discovered.

Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true? A. All the stars in the cluster will be of about the same mass. B. A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage. C. All the stars in the cluster will become main-sequence stars at about the same time. D. All the stars in the cluster will have approximately the same luminosity and surface temperature.

B. A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage. Very massive stars can form in a million years or less, and then live just a few million years. Low-mass stars take tens of millions of years — or more — just to reach the beginning of their main-sequence lives.

You observe a full moon rising at sunset. What will you see at midnight? A. A first quarter moon B. A full moon high in the sky C. A waning gibbous moon D. A third quarter moon

B. A full moon high in the sky

Generally speaking, how does the surface temperature and luminosity of a protostar compare to the surface temperature and luminosity of the main-sequence star it becomes? A. A main-sequence star is cooler and dimmer than it was as a protostar. B. A main-sequence star is hotter and dimmer than it was as a protostar. C. A main-sequence star is cooler and brighter than it was as a protostar. D. A main-sequence star is hotter and brighter than it was as a protostar.

B. A main-sequence star is hotter and dimmer than it was as a protostar. The protostar is actually brighter than the main-sequence star because it is so much larger in size (radius).

Which of the following scenarios involves energy that we would typically calculate with Einstein's formula E = mc 2? A. A burning piece of wood produces light and heat, therefore giving off radiative and thermal energy. B. A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium. C. A mass raised to a great height has a lot of gravitational potential energy. D. An object accelerated to a great speed has a lot of kinetic energy.

B. A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium.

Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply? A. Active galactic nuclei can form only at large distances from the Milky Way. B. Active galactic nuclei tend to become less active as they age. C. Supermassive black holes existed only when the universe was young, and no longer exist today. D. The jets seen in many active galactic nuclei must cause them to move far away from us.

B. Active galactic nuclei tend to become less active as they age. Remember that at large distances we are seeing into the past. The fact that active galactic nuclei are far away means that they are young. The galaxies we see nearby are older. We conclude that activity is more common among young galaxies than older ones.

Why are astronauts weightless in the Space Station? A. Because there is no gravity in space B. Because the Space Station is constantly in free-fall around the Earth C. Because the Space Station is moving at constant velocity D. Because the Space Station is traveling so fast

B. Because the Space Station is constantly in free-fall around the Earth

Why can't we see past the cosmological horizon? A. Every galaxy in the entire universe (not just the observable universe) exists within the cosmological horizon, so there's nothing to see beyond it. B. Beyond the cosmological horizon, we would be looking back to a time before the universe was born. C. We do not have big enough telescopes. D. The cosmological horizon is infinitely far away, and we can't see to infinity.

B. Beyond the cosmological horizon, we would be looking back to a time before the universe was born.

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 looking for the splitting of spectral lines in the Sun's spectrum C. Only by using sophisticated computer models, because there are no observational ways of measuring magnetic field strength D. By observing auroras here on Earth

B. By looking for the splitting of spectral lines in the Sun's spectrum Magnetic fields can cause some spectral lines to split, so we can measure the Sun's magnetic field strength by measuring the splitting of spectral lines. (This splitting of spectral lines is often called the Zeeman effect.)

Suppose Earth were to cool down a little. How would the carbon dioxide cycle tend to restore temperatures to normal? A. Cooler temperatures allow carbon dioxide to form rain and rain out of the atmosphere. B. Cooler temperatures lead to slower formation of carbonate minerals in the ocean, so carbon dioxide released by volcanism builds up in the atmosphere and strengthens the greenhouse effect. C. Cooler temperatures mean more ice and more erosion, which somehow makes the planet warm up. D. Cooler temperatures cause volcanoes to become more active, so they release more carbon dioxide into the atmosphere than they do when temperatures are warmer.

B. Cooler temperatures lead to slower formation of carbonate minerals in the ocean, so carbon dioxide released by volcanism builds up in the atmosphere and strengthens the greenhouse effect.

Some people wish that we lived in a recollapsing universe that would eventually stop expanding and start contracting. Based on current understanding, which of the following would have to be true for this to be the case? A. The total density of matter equals the critical density. B. Dark energy does not exist and there is much more matter than current evidence suggests. C. Dark energy is the dominant form of energy in the cosmos. D. The density of dark matter turns out to be greater than the density of dark energy.

B. Dark energy does not exist and there is much more matter than current evidence suggests. We'd need the extra dark matter to put the density over the critical density and the lack of dark energy so that the expansion does not accelerate.

Which of the following represents a case in which you are not accelerating? A. Driving 60 miles per hour around a curve B. Driving in a straight line at 60 miles per hour C. Slamming on the brakes to come to a stop at a stop sign D. Going from 0 to 60 miles per hour in 10 seconds

B. Driving in a straight line at 60 miles per hour This is constant velocity, which means zero acceleration.

Why does Earth have so little carbon dioxide in its atmosphere compared to Venus? A. Earth once had a lot of carbon dioxide, but it was lost to space during the heavy bombardment early in our solar system's history. B. Earth has just as much carbon dioxide as Venus, but most of it is locked up in carbonate rocks rather than being free in the atmosphere. C. Earth's volcanoes outgassed far less carbon dioxide than those on Venus. D. Chemical reactions turned Earth's carbon dioxide into nitrogen.

B. Earth has just as much carbon dioxide as Venus, but most of it is locked up in carbonate rocks rather than being free in the atmosphere.

During the period each year when we see Mars undergoing apparent retrograde motion in our sky, what is really going on in space? A. Earth and Mars are getting closer together. B. Earth is catching up with and passing by Mars in their respective orbits. C. Earth and Mars are on opposite sides of the Sun. D. Mars is moving around the Sun in the opposite direction from which Earth is moving around the Sun.

B. Earth is catching up with and passing by Mars in their respective orbits.

For most of history, the lack of observable stellar parallax was interpreted to mean that __________. A. Galileo's theories of the universe were essentially correct B. Earth is stationary at the center of the universe C. stars must all lie at the same distance from Earth, on the celestial sphere D. stars were too far away for parallax to be measured with available technology

B. Earth is stationary at the center of the universe

Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star? A. The red giant is more massive. B. Fusion reactions are producing energy at a greater rate in the red giant. C. The red giant has a hotter core. D. The red giant's surface is hotter.

B. Fusion reactions are producing energy at a greater rate in the red giant.

How are galaxies important to our existence? A. Without galaxies, the universe could not be expanding. B. Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist. C. Without galaxies, there could not have been a Big Bang. D. Deep in their centers, galaxies created the elements from which we are made.

B. Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist.

Why didn't a planet form where the asteroid belt is now located? A. The temperature in this portion of the solar nebula was just right to prevent rock from sticking together. B. Gravitational tugs from Jupiter prevented material from collecting together to form a planet. C. There was too much rocky material to form a terrestrial planet, but not enough gaseous material to form a jovian planet. D. There was not enough material in this part of the solar nebula to form a planet.

B. Gravitational tugs from Jupiter prevented material from collecting together to form a planet.

All the following statements are true. Which one is most important in explaining the tremendous tidal heating that occurs on Io? A. Io exhibits synchronous rotation, meaning that its rotation period and orbital period are the same. B. Io orbits Jupiter on an elliptical orbit, due to orbital resonances with other satellites. C. Io orbits Jupiter in the Io torus, and therefore has a surface that is bombarded by many charged particles. D. Io is the closest to Jupiter of Jupiter's large moons.

B. Io orbits Jupiter on an elliptical orbit, due to orbital resonances with other satellites. On an elliptical orbit, tides vary and flex Io's shape.

Which of the following best describes how the Drake equation is useful? A. It tells us what wavelengths of light will be most useful to examine in the search for extraterrestrial intelligence. B. It helps us understand what we need to know in order to determine the likelihood of finding other civilizations. C. It has allowed us to determine the number of civilizations in the Milky Way Galaxy. D. It allows us to calculate the masses of planets orbiting other stars.

B. It helps us understand what we need to know in order to determine the likelihood of finding other civilizations.

Most nearby stars move relative to the Sun at speeds below about 30 km/s. Suppose you observe a nearby star that is moving much faster than this (say, 300 km/s). Which of the following is a likely explanation for its high speed? A. It has been pushed to high speed by the shock wave from a nearby supernova. B. It is probably a halo star that is currently passing through the disk. C. It is a very young star, recently formed. D. It is a very high mass star.

B. It is probably a halo star that is currently passing through the disk. All the disk stars in our vicinity should be orbiting the galactic center at about the same speed, which is why their speeds relative to the Sun are fairly low. Halo stars have very different orbits, so when they pass through the disk they have high speeds relative to the nearby disk stars.

Which of the following best describes natural selection? A. It is the idea that organisms naturally increase in complexity and intelligence with time. B. It is the idea that organisms with genetic traits that improve their ability to reproduce are more likely to pass those traits on to future generations. C. It is a guess made by scientists about how life develops, but it has no hard evidence to support it. D. It is the idea that the strong survive and the weak die off.

B. It is the idea that organisms with genetic traits that improve their ability to reproduce are more likely to pass those traits on to future generations. We say that these traits are "selected" for because of the advantages they confer.

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 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. C. It predicted that the Sun would shrink noticeably as we watched it, but the Sun appears to be stable in size. D. It is physically impossible to generate heat simply by making a star shrink 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.

What is Pluto's moon Charon thought to have in common with our own Moon? A. It has the same approximate mass. B. It probably formed as a result of a giant impact. C. It has the same basic composition. D. It has the same average density.

B. It probably formed as a result of a giant impact.

How would you expect a star that formed recently in the disk of the galaxy to differ from one that formed early in the history of the disk? A. It should orbit the galactic center at a much higher rate of speed. B. It should have a higher fraction of elements heavier than hydrogen and helium. C. All of the above would be expected. D. It should be higher in mass. E. It should be much brighter.

B. It should have a higher fraction of elements heavier than hydrogen and helium.

All the following statements about Mars are true. Which one might have led to a significant loss of atmospheric gas to space? A. The axis tilt of Mars is thought to change significantly with time. B. Mars lost any global magnetic field that it may once have had. C. Mars probably once had a much higher density of greenhouse gases in its atmosphere than it does today. D. Outgassed water molecules are split apart, and the oxygen then reacts chemically with surface rock on Mars.

B. Mars lost any global magnetic field that it may once have had.

Which of the following statements comparing halo stars to our Sun is not true? A. Most stars in the halo are less luminous than the Sun. B. Most stars in the halo have either died or are in their final stages of life, while the Sun is only in about the middle of its lifetime. C. Most stars in the halo contain a much lower percentage of heavy elements than the Sun. D. Most stars in the halo have cooler surface temperatures than the Sun.

B. Most stars in the halo have either died or are in their final stages of life, while the Sun is only in about the middle of its lifetime. This is not true of most of the stars, because most stars are less massive than the Sun and therefore progress through their stages of life at a much slower rate than the Sun. These very low-mass stars have more of their main-sequence lives remaining than the Sun, despite their greater ages.

A computer accessory salesman attempts to convince you to purchase a "solar neutrino" shield for your new computer. (It's even "on sale"!) Why do you turn down this excellent offer? A. The Earth's natural magnetic field already offers excellent protection against the onslaught of solar neutrinos. B. Neutrinos rarely, if ever, interact with your computer. C. There's no such thing as a solar neutrino. D. Solar neutrinos are generated by solar winds, but we're in a solar minimum now, so the risk of damage is very low.

B. Neutrinos rarely, if ever, interact with your computer. In fact, neutrinos rarely interact with matter of any kind, so it would be pointless to have a neutrino shield, even if such a shield were possible (which it's not, since the neutrinos won't interact with the shield either).

Does Hubble's law work well for galaxies in the Local Group? Why or why not? A. No, because Hubble did not know the Local Group existed when he discovered his law. B. No, because galaxies in the Local Group are gravitationally bound together. C. Yes, it works so well that we have never detected any measurable deviations from its predictions. D. No, because we do not know the precise value of Hubble's constant.

B. No, because galaxies in the Local Group are gravitationally bound together. The universe as a whole is expanding, but structures held together by gravity (or other forces) are not.

Is space expanding within clusters of galaxies? A. No, because the universe is not old enough yet for these objects to have begun their expansion. B. No, because their gravity is strong enough to hold them together even while the universe as a whole expands. C. Yes, and that is why clusters tend to grow in size with time. D. No, because expansion of the universe affects only empty space, not space in which matter is present.

B. No, because their gravity is strong enough to hold them together even while the universe as a whole expands. Gravity has overcome expansion in individual galaxies and galaxy clusters, but not for the universe as a whole. That is why the universe continues to expand, but galaxies and galaxy clusters do not.

Based on everything you have learned about the formation of our solar system, which of the following statements is probably not true? A. Within a star's planetary system, all its planets will tend to orbit in the same direction and approximately the same plane. B. Only a tiny percentage of stars are surrounded by spinning disks of gas during their formation. C. Planets are common, and many or most stars have them. D. Other planetary systems will have far more numerous asteroids and comets than actual planets.

B. Only a tiny percentage of stars are surrounded by spinning disks of gas during their formation.

Which of the following objects are probably not located in the same general region of the solar system in which they originally formed? A. Kuiper belt comets B. Oort cloud comets C. asteroids of the asteroid belt D. Pluto

B. Oort cloud comets

According to current science, why didn't oxygen begin to accumulate in the atmosphere for more than a billion years after life appeared on the Earth? A. Early forms of animal life consumed the oxygen released by plants during the first billion years of life on Earth. B. Oxygen was removed from the atmosphere by chemical reactions with surface rocks as quickly as it was released by life. C. Oxygen was removed from the atmosphere by dissolving in the ocean as quickly as it was released by life. D. Early life did not release oxygen, and oxygen releasing organisms didn't evolve for a billion years after the earliest life.

B. Oxygen was removed from the atmosphere by chemical reactions with surface rocks as quickly as it was released by life. Oxygen could buildup only when the surface rock had absorbed as much oxygen as it could.

Which of the following is not a piece of evidence supporting the idea that Pluto is a large comet of the Kuiper belt? A. Pluto is not the largest object orbiting in the region of the Kuiper belt. B. Pluto grows a coma and a long tail when it is at the point in its orbit closest to the Sun. C. Pluto's orbit is very similar to the orbits of other known Kuiper belt comets. D. Triton, which must once have orbited the Sun before being captured by Neptune, is significantly larger than Pluto. E. Pluto's composition appears to match that of other known Kuiper belt comets.

B. Pluto grows a coma and a long tail when it is at the point in its orbit closest to the Sun.

How do scientists determine the age of the solar system? A. Radiometric dating of the oldest Earth rocks B. Radiometric dating of meteorites C. Radiometric dating of Moon rocks D. Theoretical calculations tell us how long it has taken the planets to evolve to their present forms

B. Radiometric dating of meteorites The oldest meteorites are presumed to be material that condensed early in the history of the solar system and therefore represent the time at which the planets began to form.

Where is our solar system located within the Milky Way Galaxy? A. In the halo of the galaxy B. Roughly halfway between the center and the edge of the visible disk of the galaxy C. At the far edge of the galaxy's visible disk D. Very near the center of the galaxy

B. Roughly halfway between the center and the edge of the visible disk of the galaxy The disk is about 100,000 light-years in diameter, which means about 50,000 light-years in radius. Therefore, the Sun's distance of about 28,000 light-years from the galactic center puts it a little over halfway out through the disk.

The choices below describe four hypothetical planets. Which one's surface would you expect to be most crowded with impact craters? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) A. Size: same as Mars. Distance from Sun: same as Earth. Rotation rate: once every 18 hours. B. Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days. C. Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours. D. Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months.

B. Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days. The smallest size means the least geological activity to have erased past impact craters, so lots of craters would still be present.

Suppose a scientist holds a press conference at which he claims that 10% of the matter in the Milky Way is in the form of dust grains. Does his claim seem reasonable? Why or why not? A. The 10% figure is too low, because most of the mass of the galaxy is in the form of interstellar dust. B. The 10% figure is too high because there are not enough heavy elements to make that much dust. C. It seems reasonable as long as we assume that red giant stars - which produce dust grains in their stellar winds - are more common than we thought. D. It is reasonable, because we already know that interstellar dust obscures our view through the disk of the galaxy.

B. The 10% figure is too high because there are not enough heavy elements to make that much dust. Dust grains are made of heavier elements, not from the hydrogen and helium that make up 98% of the chemical content of the galaxy. In fact, dust represents only about 1% of the mass in molecular clouds.

How does the Sun's mass compare to Earth's mass? A. The Sun's mass is about 30 times the mass of the Earth. B. The Sun's mass is about 300,000 times the mass of the Earth. C. Both have approximately the same mass. D. The Sun's mass is about 300 times the mass of the Earth.

B. The Sun's mass is about 300,000 times the mass of the Earth.

Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude? A. The X-ray source must have a strong, rapidly varying magnetic field. B. The X-ray source is no more than a few light-days in diameter. C. The X-ray source is a quasar. D. The X-ray source contains a black hole with an accretion disk.

B. The X-ray source is no more than a few light-days in diameter.

Based on current evidence, how does the actual average density of matter in the universe compare to the critical density? A. If we include dark matter, the actual average density of matter equals the critical density. B. The actual average density of matter, even with dark matter included, is only about a quarter of the critical density. C. The actual average density of matter less than 1% of the critical density. D. The actual density of average matter is about twice the critical density.

B. The actual average density of matter, even with dark matter included, is only about a quarter of the critical density. Nevertheless, evidence now suggests that the total density of matter and energy equals the critical density, which means that about three-quarters of the critical density must be made up of so-called dark energy.

The following statements are all true. Which one counts as an "exception to the rule" in being unusual for our solar system? A. Venus does not have a moon. B. The diameter of Earth's Moon is about 1/4 that of Earth. C. Jupiter has a very small axis tilt. D. Saturn has no solid surface.

B. The diameter of Earth's Moon is about 1/4 that of Earth.

Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town? A. It would crash into Earth, throwing vast amounts of dust into the atmosphere that, in turn, would cool the Earth; this is probably what caused the extinction of the dinosaurs. B. The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. C. The combined mass of Earth and the neutron star would cause the neutron star to collapse into a black hole. D. It would rapidly sink to the center of Earth.

B. The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. The neutron star is far more massive than Earth, so Earth would end up wrapped around it and compressed to extremely high density.

Many meteorites appear to have formed very early in the solar system's history. How do these meteorites support our theory about how the terrestrial planets formed? A. Their appearance and composition matches what we observe in comets today, suggesting that they were once pieces of icy planetesimals. B. The meteorites appearance and composition is just what we'd expect if metal and rock condensed and accreted as our theory suggests. C. Their overall composition is just what we believe the composition of the solar nebula to have been: mostly hydrogen and helium. D. The meteorites sizes are just what we'd expect if metal and rock condensed and accreted as our theory suggests.

B. The meteorites appearance and composition is just what we'd expect if metal and rock condensed and accreted as our theory suggests.

All the following statements are true. Which one explains the reason that there is not a solar eclipse at every new moon? A. The Moon goes through a complete cycle of phases about every 29 1/2 days. B. The orbital plane of the Moon is tilted slightly (by about 5 degrees) to the ecliptic plane. C. The nodes of the moon's orbit precess with an 18-year period. D. The Moon is only about 1/4 as large as Earth in diameter.

B. The orbital plane of the Moon is tilted slightly (by about 5 degrees) to the ecliptic plane.

What is the best evidence for an extremely massive black hole in the center of the Milky Way? A. The center of our galaxy hosts a pulsar that is spinning so fast that it could only be a black hole. B. The orbits of stars in the center of the galaxy indicate that the presence of an approximately 4 million solar mass object in a region no larger than our solar system. C. We observe stars vanishing in the center of the Galaxy as they are sucked into the black hole. D. Huge amounts of X-rays are pouring out of the center of the galaxy.

B. The orbits of stars in the center of the galaxy indicate that the presence of an approximately 4 million solar mass object in a region no larger than our solar system.

Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet's year (orbital period) compare to Earth's year? A. An orbit at a distance of 1 AU would not be possible around a star more massive than the Sun. B. The planet's year would be shorter than Earth's. C. The planet's year would be the same as Earth's. D. The planet's year would be longer than Earth's.

B. The planet's year would be shorter than Earth's.

Which of the following statements about spectral types of stars is not generally true? A. The spectral type of a star can be used to determine its color. B. The spectral type of a star can be used to determine its distance. C. The spectral type of a star can be determined by identifying lines in its spectrum. D. The spectral type of a star can be used to determine its surface temperature.

B. The spectral type of a star can be used to determine its distance. Spectral type tells us surface temperature, but to calculate the star's distance we need to know its luminosity and apparent brightness (and then use the inverse square law for light).

How did star formation likely proceed in the protogalactic cloud that formed the Milky Way? A. The protogalactic cloud gradually formed stars, starting from the center of the galaxy working outwards. B. The stars that formed first could orbit the center of the galaxy in any direction at any inclination. C. The protogalactic cloud gradually formed stars, starting from the outer edges of the spiral arms and working inward. D. The stars that formed first eventually settled into a galactic disk, circling the center of the galaxy.

B. The stars that formed first could orbit the center of the galaxy in any direction at any inclination. That is why these stars now make up the halo.

Why does Jupiter have three distinct layers of clouds? A. Clouds form randomly, so on average there are always three layers. B. The three layers represent clouds made of gases that condense at different temperatures. C. The three layers reflect regions of Jupiter's atmosphere with different overall chemical compositions. D. Jupiter has three different types of wind, each of which makes a different type of cloud.

B. The three layers represent clouds made of gases that condense at different temperatures. The three cloud layers are ammonia, ammonium hydrosulfide, and water. Each of these gases condenses at a different temperature and hence at a different altitude in Jupiter's atmosphere.

How should we expect the Milky Way's interstellar medium to be different in 50 billion years than it is today? A. The total amount of gas will be much greater, since many stars will undergo supernovae between now and then. B. The total amount of gas will be much less than it is today. C. The total amount of gas will be about the same, but the percentage of elements heavier than hydrogen and helium will have risen from the current 2% to more than 50%. D. Thanks to the recycling of the star-gas-star cycle, the interstellar medium should look about the same in 50 billion years as it does today.

B. The total amount of gas will be much less than it is today. With each subsequent generation of stars, some material is "locked away" permanently in brown dwarfs and stellar corpses. Thus, the amount of gas available for recycling gradually declines with time.

Suppose you heat an oven to 400°F 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 molecules in the water are moving faster than the molecules in the oven. B. The water can transfer heat to your arm more quickly than the air. C. The water has a higher temperature than the oven. D. The oven has a higher temperature than the water.

B. The water can transfer heat to your arm more quickly than the air. The boiling water has a lower temperature (212°F) than the air in the hot oven (400°F), but because it is much more dense, heat is transferred to your arm at a higher rate due to the more frequent collisions between your arm and the water molecules.

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. There is a balance within the Sun between the outward push of pressure and the inward pull of gravity. C. The Sun always has the same amount of mass, creating the same gravitational force. D. The Sun maintains a steady temperature.

B. There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.

About 2% of our solar nebula consisted of elements besides hydrogen and helium. However, the very first generation of star systems in the universe probably consisted only of hydrogen and helium. Which of the following statements is most likely to have been true about these first-generation star systems? A. Like the jovian planets in our solar system, the jovian planets in these first-generation systems were orbited by rings. B. There were no comets or asteroids in these first-generation star systems. C. Jovian planets in these first-generation star systems had clouds made of water and other hydrogen compounds. D. These first-generation star systems typically had several terrestrial planets in addition to jovian planets.

B. There were no comets or asteroids in these first-generation star systems. Asteroids are made from metal and rock, and comets are made mostly of frozen hydrogen compounds - and all these materials require elements besides hydrogen and helium.

Current evidence suggests that some massive jovian planets orbit at very close orbital distances to their stars. How do we think these planets ended up on these close orbits? A. These planets were able to form close to their stars because their solar nebulas were very cold in temperature. B. These planets migrated inward after being born on orbits much farther from their stars. C. Despite their large masses, these planets are made of rock and metal and therefore could form in their inner solar systems. D. These planets were captured from other solar systems.

B. These planets migrated inward after being born on orbits much farther from their stars.

Which of the following statements best explains what we mean when we say that the electroweak and strong forces "froze out" at 10-38 second after the Big Bang? A. Freezing out was a term coined by particle physicists who think that the Big Bang theory is really cool. B. These two forces first became distinct at this time. C. Following this time, neither the strong nor electroweak forces were ever important in the universe again. D. These forces are important only at temperatures below the freezing point of water - a temperature that the universe reached at an age of about at 10-38 second.

B. These two forces first became distinct at this time. Prior to this time, the electroweak and strong forces were indistinguishable from each other, but after this time they behaved differently from each other.

Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? A. The clock will fall faster and faster, reaching the speed of light as it crosses the event horizon. B. Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted. C. Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted. D. The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes.

B. Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.

Which jovian planet should have the most extreme seasonal changes? A. Neptune B. Uranus C. Jupiter D. Saturn

B. Uranus

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

B. We can send a space probe into the Sun's photosphere.

How do we know that galaxy clusters contain a lot of mass in the form of hot gas that fills spaces between individual galaxies? A. We infer its existence by observing its gravitational effects on the galaxy motions. B. We detect this gas with X-ray telescopes. C. The hot gas shows up as bright pink in visible-light photos of galaxy clusters. D. We can observe the frictional effects of the hot gas in slowing the speeds of galaxies in the clusters.

B. We detect this gas with X-ray telescopes. The hot gas emits X rays, so we can "see" it with X-ray telescopes. Measurements indicate that the total mass in the hot gas exceeds the amount of matter in stars within the galaxies (but it is less than the amount of dark matter).

To date, we've found very few planets orbiting their stars at distances comparable to the distances of the jovian planets in our solar system. Why do astronomers think this is the case? A. Planets at such distances are probably very low in mass. B. We have not yet been searching for planets at such distances for a long enough time. C. No known method can detect planets at such large distances. D. Planets at such distances are extremely rare.

B. We have not yet been searching for planets at such distances for a long enough time.

The Chandra X-ray Observatory must operate in space because: A. It was built by NASA. B. X rays do not penetrate Earth's atmosphere. C. X-ray telescopes require the use of grazing incidence mirrors. D. X rays are too dangerous to be allowed on the ground.

B. X rays do not penetrate Earth's atmosphere.

Which of the following has your "cosmic address" in the correct order? A. You, Earth, solar system, Local Group, Milky Way Galaxy, Local Supercluster, universe B. You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe C. You, Earth, solar system, Local Group, Local Supercluster, Milky Way Galaxy, universe D.You, Earth, Local Group, Local Supercluster, solar system, Milky Way Galaxy, universe E. You, Earth, Milky Way Galaxy, solar system, Local Group, Local Supercluster, universe

B. You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe

The planets never travel in a straight line as they orbit the Sun. According to Newton's second law of motion, this must mean that __________. A. the planets will eventually fall into the Sun B. a force is acting on the planets C. the planets have angular momentum D. the planets are always accelerating

B. a force is acting on the planets

One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be __________. A. an elliptical galaxy B. a spiral galaxy C. an irregular galaxy D. a torn and incoherent galaxy

B. a spiral galaxy With a lot of angular momentum, the protogalactic cloud would spin more rapidly as it collapsed, leading to the formation of a disk - which makes it a spiral galaxy.

When we look at an object that is 1,000 light-years away we see it _________. A. as it was 1,000 light-years ago B. as it was 1,000 years ago C. looking just the same as our ancestors would have seen it 1,000 years ago D. as it is right now, but it appears 1,000 times dimmer

B. as it was 1,000 years ago

Astronomers infer that the universe is expanding because distant galaxies all appear to __________. A. rotate rapidly B. be moving away from us, with more distant ones moving faster C. be made mostly of dark matter D. be growing in size

B. be moving away from us, with more distant ones moving faster

Where would a brown dwarf be located on an H-R diagram? A. above and to the left of the highest part of the main sequence B. below and to the right of the lowest part of the main sequence C. in the lower left corner of the H-R diagram D. in the upper right corner of the H-R diagram

B. below and to the right of the lowest part of the main sequence

Which of the following is most unlikely to be found on Titan? A. volcanic outgassing of methane and other gases B. lakes of liquid water in the warmer equatorial regions C. lakes of liquid methane ethane D. rain or snow consisting of methane or ethane droplets or ice crystals

B. lakes of liquid water in the warmer equatorial regions Titan's surface temperature is never anywhere close to being warm enough for liquid water, even at its equator.

An angle of 1 arcsecond is __________. A. about the width of a finger held at arm's length B. less than the thickness of a human hair held at arm's length C. about the width of your fist held at arm's length D. slightly more than the width of a basketball held at arm's length

B. less than the thickness of a human hair held at arm's length Because there are 60 arcminutes in 1 degree and 60 arcseconds in 1 arcminute, there are 3,600 arcseconds in 1 degree. If you then remember that 1 degree is about the width of a finger at arm's length, you'll see that 1 arcsecond is indeed about the width of a human hair at arm's length.

Compared to the distance between Earth and Mars, the distance between Jupiter and Saturn is __________. A. about the same B. much larger C. much smaller D. just slightly less

B. much larger

What are the two geological features that appear to set Earth apart from other terrestrial worlds in our solar system? A. mantle convection and a thick atmosphere B. plate tectonics and a high level of erosion C. significant volcanism and tectonics D. a dense core and plate tectonics

B. plate tectonics and a high level of erosion

A star's color is related to it's surface temperature because __________. A. the colors of stars depend mainly on the emission lines in the spectra B. stars emit thermal radiation C. the color of a star depends on its mass, and mass is related to surface temperature. D. stars have absorption lines in their spectra

B. stars emit thermal radiation The color of a star depends primarily on where its thermal radiation spectrum peaks. (Recall that thermal radiation peaks at a wavelength that depends on temperature.)

A spinning neutron star has been observed at the center of a _________. A. planetary nebula B. supernova remnant C. red supergiant D. protostar

B. supernova remnant

Suppose you see a photo showing Jupiter half in sunlight and half in shadow (that is, a first quarter Jupiter). This photo might have been taken by _________. A. the Arecibo radio telescope in Puerto Rico B. the Galileo spacecraft that orbited Jupiter in the 1990s C. the Hubble Space Telescope (which orbits Earth) D. the Keck telescope on Mauna Kea, Hawaii

B. the Galileo spacecraft that orbited Jupiter in the 1990s As the spacecraft orbited Jupiter, it saw Jupiter go through all the phases.

How is Einstein's famous equation, E = mc 2, important in understanding the Sun? A. the Sun is extremely massive B. the Sun generates energy to shine by losing 4 million tons of mass each second C. the Sun's surface temperature is about 6,000° Celsius D. the Sun has a magnetic field strong enough to influence the atmospheres of the planets

B. the Sun generates energy to shine by losing 4 million tons of mass each second

Carbon fusion occur in high-mass stars but not in low-mass stars because _________. A. carbon fusion can occur only in the stars known as carbon stars B. the cores of low-mass stars never get hot enough for carbon fusion C. only high-mass stars do fusion by the CNO cycle D. the cores of low-mass stars never contain significant amounts of carbon

B. the cores of low-mass stars never get hot enough for carbon fusion

A quasar's spectrum is hugely redshifted. What does this large redshift tells us about the quasar? A. the size of the quasar's central, supermassive black hole B. the distance to the quasar C. the type of host galaxy in which the quasar resides D. the composition of the quasar

B. the distance to the quasar

Laboratory experiments conducted with particle accelerators confirm predictions made by the theory that unifies _________. A. the strong and weak forces into the combined nuclear force B. the electromagnetic and weak forces into the electroweak force C. the strong, weak, and electromagnetic forces into the GUT force D. the unification of all four forces into a single "superforce"

B. the electromagnetic and weak forces into the electroweak force This is the only unification of the four forces that has so far been verified in the laboratory.

In a photo like the Hubble Deep Field (Figure 16.1 in your textbook), we see galaxies in many different stages of their lives. In general, which galaxies are seen in the earliest (youngest) stages of their lives? A. the galaxies that are nearest to us B. the galaxies that are farthest away C. the galaxies that are the reddest in color D. the galaxies that have the most hot, young O and B stars

B. the galaxies that are farthest away Remember that the farther we look into space, the farther back in time we are seeing. Thus the most distant galaxies are the ones we see in the most distant past, when both they and the universe were much younger.

Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes significantly dimmer for about 2 hours. The most likely explanation is that __________. A. the star is periodically ejecting gas into space, every 73 hours B. the star is a member of an eclipsing binary star system C. the star is a white dwarf D. the star is a Cepheid variable

B. the star is a member of an eclipsing binary star system

Suppose that Earth's atmosphere had no greenhouse gases. Then Earth's average surface temperature would be __________. A. about the same as it is now B. well below the freezing point of water C. slightly warmer, but still well below the boiling point of water D. slightly cooler, but still above freezing

B. well below the freezing point of water

Which of the following correctly lists two key pieces of evidence that, together, indicate that we should expect human activity to cause global warming? A. (1) We can learn about past climate from ice cores; (2) Ice cores show that Earth naturally has cooler and warmer periods. B. (1) The carbon dioxide cycle regulates Earth's climate; (2) Human activity has disrupted the carbon dioxide cycle. C. (1) Carbon dioxide tends to make planets warmer than they would be otherwise; (2) Measurements demonstrate that human activity is raising the carbon dioxide concentration in the atmosphere. D. (1) The burning of fossil fuels is a form of human activity; (2) Human activity is always bad for the environment.

C. (1) Carbon dioxide tends to make planets warmer than they would be otherwise; (2) Measurements demonstrate that human activity is raising the carbon dioxide concentration in the atmosphere.

Suppose a comet orbits the Sun on a highly eccentric orbit with an average (semimajor axis) distance of 1 AU. How long does it take to complete each orbit, and how do we know? A. It depends on the eccentricity of the orbit, as described by Kepler's second law. B. It depends on the eccentricity of the orbit, as described by Kepler's first law. C. 1 year, which we know from Kepler's third law. D. Each orbit should take about 2 years, because the eccentricity is so large.

C. 1 year, which we know from Kepler's third law. Kepler's third law tells us that any object with the same average distance as Earth will orbit in the same time of 1 year.

Which of the following is not part of a good scientific theory? A. A scientific theory should be based on natural processes and should not invoke the supernatural or divine. B. A scientific theory must explain a wide variety of phenomena observed in the natural world. C. A scientific theory cannot be accepted until it has been proven true beyond all doubt. D. A scientific theory must make testable predictions that, if found to be incorrect, could lead to its own modification or demise.

C. A scientific theory cannot be accepted until it has been proven true beyond all doubt.

Suppose the planet Uranus were much brighter in the sky, so that it was as easily visible to the naked eye as Jupiter or Saturn. Which one of the following statements would most likely be true in that case? A. Its gravity would cause the tides to be much higher than they actually are. B. Its brightness would make it possible to read by starlight at night. C. A week would have eight days instead of seven. D. Its slow motion through the sky would have led it to be named after the Goddess of Procrastination. E. The discovery that the Earth is a planet going around the Sun would have come hundreds of years earlier.

C. A week would have eight days instead of seven. A week has seven days because seven naked-eye objects appear to move among the stars: the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn. If Uranus had been an eighth object visibly moving among the stars, a week very likely would have eight days.

Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen-16, neon-20, and magnesium-24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case? A. Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between. B. This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang. C. At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions. D. The apparent pattern is thought to be a random coincidence.

C. At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions. Helium has atomic mass number 4, so each subsequent reaction tends to make an element with an atomic mass number divisible by 4.

In what way is Venus most similar to Earth? A. Both planets have very similar atmospheres. B. Both planets have warm days and cool nights. C. Both planets are nearly the same size. D. Both planets have similar surface geology.

C. Both planets are nearly the same size. This similarity in size means the two planets are probably quite similar in their interior structures and fundamental properties, though they have obvious and important differences on their surfaces.

In 1924, Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way, thus putting to rest the idea that it might have been a cloud within our own galaxy. How was he able to prove this? A. He was able to measure the parallax of the Andromeda Galaxy. B. He found that the universe is expanding, and therefore concluded that Andromeda must lie outside our own galaxy. C. By observing individual Cepheid variable stars in Andromeda and applying the period-luminosity relation D. He was the first person ever to look through a telescope at the object we now call the Andromeda Galaxy.

C. By observing individual Cepheid variable stars in Andromeda and applying the period-luminosity relation By measuring their periods, the period--luminosity told him their luminosities. He could then calculate their distances by comparing their luminosities and their apparent brightnesses with the inverse square law for light.

According to the Big Bang theory, why do we live in a universe that is made of almost entirely of matter rather than antimatter? A. GUT theories predict that under the conditions that prevailed in the early universe, the normal laws of physics would have been suspended so that only matter particles were created, and no particles of antimatter. B. The fact that we live in a universe made of matter is not surprising, because antimatter has never been shown to exist for real. C. During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles. D. Einstein's famous equation E = mc 2 tells us that energy can turn into matter, but does not tell us that it can turn into antimatter.

C. During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles. The excess was only about 1 extra matter particle for every billion particles of matter and antimatter, and the annihilation of the rest of the billion explains why there are so many photons in the universe.

Suppose that the Sun shrank in size but that its mass remained the same. What would happen to the orbit of the Earth? A. The size of Earth's orbit would shrink, and it would take less than one year to orbit the Sun. B. Earth would change from a bound orbit to an unbound orbit and fly off into interstellar space. C. Earth's orbit would be unaffected. D. Earth's orbit would expand, and it would take more than one year to orbit the Sun.

C. Earth's orbit would be unaffected.

Only one of the statements below uses the term theory in its correct, scientific sense. Which one? A. Evolution is only a theory, so there's no reason to think it really happened. B. I wrote a theory that is 152 pages long. C. Einstein's theory of relativity has been tested and verified thousands of times. D. I have a new theory about the cause of earthquakes, and I plan to start testing it soon.

C. Einstein's theory of relativity has been tested and verified thousands of times.

It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy. Why? A. Elliptical galaxies contain much less dark matter than spiral galaxies, so it's much more difficult to measure. B. We cannot observe spectral lines for elliptical galaxies. C. Elliptical galaxies lack the atomic hydrogen gas that we use to determine orbital speeds at great distances from the centers of spiral galaxies. D. Stars in elliptical galaxies are dimmer, making them harder to study.

C. Elliptical galaxies lack the atomic hydrogen gas that we use to determine orbital speeds at great distances from the centers of spiral galaxies. In spirals, we can measure the mass to distances well beyond the visible stars by detecting the 21 cm radiation from atomic hydrogen gas. Ellipticals have very little atomic hydrogen gas, so we can measure their masses only to the distances where we can see stars.

Which of the following is not a piece of evidence supporting the idea that an impact caused the mass extinction that occurred 65 million years ago? A. Unusually large abundances of iridium and other rare metals are found in a layer of clay that dates to 65 million years ago. B. Grains of quartz formed under high pressure are found in a layer of clay that dates to 65 million years ago. C. Fossilized dinosaur bones contain fragments of rock from the impact. D. A large impact crater along the coast of Mexico dates to 65 million years ago.

C. Fossilized dinosaur bones contain fragments of rock from the impact.

The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that: A. The biggest galaxies have the most luminous quasars. B. Quasars were more common 10 billion years ago than they are today. C. Galaxy formation and supermassive black hole formation must be related somehow. D. The black hole will eventually suck in the rest of the galaxy.

C. Galaxy formation and supermassive black hole formation must be related somehow.

Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars? A. spacecraft observations of the Sun B. H-R diagrams of open clusters C. H-R diagrams of globular clusters D. observing a low-mass star over many years

C. H-R diagrams of globular clusters A globular cluster is comprised of stars that formed at about the same time, and the globular clusters in the Milky Way are full of old low-mass stars in various stages of evolution.

When is the soonest we are likely to have moderate-resolution images and spectra of Earthlike planets around other stars? A. In just a few years, through analysis of observations by the James Webb Space Telescope. B. In just a few years, through analysis of observations by the GAIA mission. C. In a decade or two, through space observatories now in the early planning stages. D. Any day now, thanks to our largest ground-based telescopes.

C. In a decade or two, through space observatories now in the early planning stages. Scientists have numerous ideas about how they might obtain such images and spectra, but budgetary limitations mean that little work is being done in these areas right now.

From the viewpoint of an alien astronomer, how does Jupiter affect observations of our Sun? A. It causes the Sun to move in a small ellipse in the sky, with the same ellipse repeated every night. B. It makes the Sun periodically appear to get dimmer and brighter. C. It causes the Sun to move in a small ellipse with an orbital period of about 12 years. D. It makes the Sun appear dimmer when viewed with infrared light.

C. It causes the Sun to move in a small ellipse with an orbital period of about 12 years.

Which of the following is not an observed characteristic of the cosmic microwave background? A. Its temperature is a little less than 3 Kelvin (3 degrees above absolute zero). B. It has a perfect thermal radiation spectrum. C. It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe. D. Its temperature is the same everywhere, except for small variations at the level of 1 part in 100,000.

C. It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe. It does not have any spectral lines.

Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury every 125 years. What can we conclude? A. It came from the Oort cloud. B. It came from the Kuiper belt. C. It has been on its current orbit for only a very short time compared to the age of our solar system. D. It has a coma and tail during most of each orbit.

C. It has been on its current orbit for only a very short time compared to the age of our solar system. Comets cannot survive more than a couple hundred passages through the inner solar system because they lose mass with each pass. So this comet cannot have been on its current orbit for more than a few tens of thousands of years.

Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground? A. It is greater. B. You are weightless. C. It is the same. D. It is less.

C. It is the same. As long as the elevator is not accelerating, your weight on a scale in the elevator will be the same whether the elevator is on the ground or rising (or falling) at constant speed.

When is/was gravitational contraction an important energy generation mechanism for the Sun? A. It has played a role throughout the Sun's history, but it was most important right after nuclear fusion began in the Sun's core. B. It is important during periods when the Sun is going from solar maximum to solar minimum. C. It was important when the Sun was forming from a shrinking interstellar cloud of gas. D. It is the primary energy generation mechanism in the Sun today.

C. It was important when the Sun was forming from a shrinking interstellar cloud of gas. The shrinkage of the cloud meant that particles were losing gravitational potential energy, which could be converted into thermal energy.

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

C. Its density would increase but its diameter would barely change.

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color? A. It is much more massive than the Sun. B. It is much brighter than the Sun. C. Its surface is cooler than the surface of the Sun. D. It is moving away from us.

C. Its surface is cooler than the surface of the Sun.

Which of the following best explains why many jovian moons have been more geologically active than the Moon or Mercury? A. The jovian moons probably have far more internal heat generated by radioactive decay than do the Moon or Mercury. B. The jovian moons are considerably larger than the Moon and Mercury and therefore have retained much more internal heat. C. Jovian moons are made mostly of ice that can melt or deform at lower temperatures than can the rock and metal that make up the Moon and Mercury. D. Because of their greater distances from the Sun, the jovian moons receive much less heat from the Sun.

C. Jovian moons are made mostly of ice that can melt or deform at lower temperatures than can the rock and metal that make up the Moon and Mercury. That is why icy worlds need far less internal heat for geological activity than rocky worlds.

Recent evidence suggests that Mars once had a global magnetic field. Assuming this is true, which of the following could explain why Mars today lacks a global magnetic field like that of Earth? A. The Martian core is made of rock, while Earth's core is made of metal. B. Mars is too far from the Sun to have a global magnetic field. C. Mars's interior has cooled so much its molten core layer no longer undergoes convection. D. Mars rotates much slower than the Earth.

C. Mars's interior has cooled so much its molten core layer no longer undergoes convection.

Which of the following is not a major pattern of motion in the solar system? A. All of the planets orbit the Sun in the same direction - counterclockwise as viewed from above Earth's north pole. B. The Sun and most of the planets rotate in the same direction in which the planets orbit the Sun. C. Nearly all comets orbit the Sun in same direction and roughly the same plane. D. Most of the solar system's large moons orbit in their planet's equatorial plane.

C. Nearly all comets orbit the Sun in same direction and roughly the same plane. This statement is untrue because comets of the Oort cloud, which are the most numerous of all comets, have randomly oriented orbits going in all directions around the Sun.

Will our Sun ever undergo a white dwarf supernova explosion? Why or why not? A. Yes, right at the end of its double-shell burning stage of life. B. No, because the Sun's core will never be hot enough to fuse carbon and other heavier elements into iron. C. No, because it is not orbited by another star. D. Yes, about a million years after it becomes a white dwarf.

C. No, because it is not orbited by another star. White dwarf supernovae occur only in close binary star systems.

Which of the following best explains why nuclear fusion requires bringing nuclei extremely close together? A. Nuclei are attracted to each other by the electromagnetic force, but this force is only strong enough to make nuclei stick when they are very close together. B. Nuclei have to be very hot in order to fuse, and the only way to get them hot is to bring them close together. C. Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold. D. Fusion can proceed only by the proton-proton chain, and therefore requires that protons come close enough together to be linked up into a chain.

C. Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold.

Assuming that our ideas about how "hot Jupiters" ended up on their current orbits are correct, why didn't our own solar system end up with any hot Jupiters? A. Our jovian planets must have migrated outward from inside the orbit of Mercury. B. Our solar nebula must have stuck around for an unusually long time after the formation of jovian planets. C. Our solar nebula must have been blown into space shortly after the formation of the jovian planets. D. The existence of Earth and the other terrestrial planets prevented the jovian planets from migrating inward.

C. Our solar nebula must have been blown into space shortly after the formation of the jovian planets.

Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun? A. The Milky Way is composed of many individual stars. B. Four moons of Jupiter. C. Phases of Venus D. Patterns of shadow and sunlight near the dividing line between the light and dark portions of the Moon's face

C. Phases of Venus Galileo's observed that Venus goes through all the phases, which cannot be explained unless Venus is orbiting the Sun. (In the Ptolemaic system, Venus's phases vary only from new to crescent and back.)

When space probe Voyager 2 passed by Saturn, its speed increased (but not due to firing its engines). What must have happened? A. Saturn's rotation must have sped up slightly. B. Voyager 2 must have dipped through Saturn's atmosphere. C. Saturn must have lost a very tiny bit of its orbital energy. D. Saturn must have captured an asteroid at precisely the moment that Voyager 2 passed by.

C. Saturn must have lost a very tiny bit of its orbital energy.

Which of the following is not consistent with the major hallmarks of science? A. A scientific model must make testable predictions. B. Science progresses through the creation and testing of models that explain observation as simply as possible. C. Science consists of proven theories that are understood to be true explanations of reality. D. Scientific explanations should be based solely on natural causes.

C. Science consists of proven theories that are understood to be true explanations of reality.

If you could count stars at a rate of about one per second, how long would it take to count all the stars in the Milky Way Galaxy? A. Several years B. Several weeks C. Several thousand years D. Several days

C. Several thousand years

The choices below describe four hypothetical planets. Which one would you expect to have the most features of erosion? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) A. Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months. B. Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days. C. Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours. D. Size: same as Mars. Distance from Sun: same as Earth. Rotation rate: once every 18 hours.

C. Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours. This planet is large enough to have had outgassing make an atmosphere, and rotates fast enough to drive winds.

How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope? A. The 8-meter telescope has 8 times the light-collecting area of the 2-meter telescope. B. The answer cannot be determined from the information given in the question. C. The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope. D. The 8-meter telescope has 4 times the light-collecting area of the 2-meter telescope.

C. The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope. The 8-meter telescope is 4 times larger in diameter, so its light collecting area is 42 = 16 times greater.

Which of the following is not evidence supporting the idea that our Moon formed as a result of a giant impact? A. The Moon has a much smaller proportion of easily vaporized materials than Earth. B. Computer simulations show that the Moon could really have formed in this way. C. The Pacific Ocean appears to be a large crater - probably the one made by the giant impact. D. The Moon's average density suggests it is made of rock much more like that of the Earth's outer layers than that of the Earth as a whole.

C. The Pacific Ocean appears to be a large crater - probably the one made by the giant impact. The Pacific Ocean is not an impact crater. Moreover, since the continents are rearranged with time, we can be sure that the giant impact occurred long, long before there was a Pacific Ocean.

What makes us think that Mars must once have had an atmosphere that was warmer and had higher surface pressure? A. The fact that parts of Mars have a lot of craters tell us that Mars must once have been much warmer. B. The presence of inactive volcanoes on Mars tells us that there must once have been a lot of outgassing, and hence a thicker atmosphere. C. The atmosphere is too cold and thin for liquid water today, yet we see evidence that water flowed on the surface in the past. D. We think it for purely theoretical reasons, based on calculations showing that the Sun has brightened with time.

C. The atmosphere is too cold and thin for liquid water today, yet we see evidence that water flowed on the surface in the past.

If the Sun's core suddenly shrank a little bit, what would happen in the Sun? A. The core would heat up, causing it to radiate so much energy that it would shrink even more. 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 density of the core would decrease, causing the core to cool off and expand.

C. The core would heat up, fusion rates would increase, the core would re-expand.

The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is the youngest? A. The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and supergiants. B. The diagram shows no main-sequence stars at all, but it has numerous supergiants and white dwarfs. C. The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants. D. The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.

C. The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants. Only O stars have died, so the cluster is no more than a few million years old.

A rock held above the ground has potential energy. As the rock falls, this potential energy is converted to kinetic energy. Finally, the rock hits the ground and stays there. What has happened to the energy? A. The rock keeps the energy inside it in the form of mass-energy. B. The energy goes into the ground, and as a result, the orbit of the Earth about the Sun is slightly changed. C. The energy goes to producing sound and to heating the ground, rock, and surrounding air. D. It is transformed back into gravitational potential energy.

C. The energy goes to producing sound and to heating the ground, rock, and surrounding air.

Which statement below correctly describes the relationship between expansion rate and age for the universe? A. The faster the rate of expansion, the older the age of the universe. B. Age is independent of the expansion rate. C. The faster the rate of expansion, the younger the age of the universe.

C. The faster the rate of expansion, the younger the age of the universe.

You discover a binary star system in which one star is a 15 M Sun main-sequence star and the other is a 10 M Sun giant. How do we think that a star system such as this might have come to exist? A. The two stars probably were once separate, but became a binary when a close encounter allowed their mutual gravity to pull them together. B. The two stars are simply evolving normally and independently, and one has become a giant before the other. C. The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion. D. Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main sequence stars millions of years later than its less massive companion.

C. The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion. The more massive star should have evolved faster and become a giant first. Once it became a giant, material "spilled over" to its companion. Thus the companion gained mass at the giant's expense, allowing it to become the more massive star.

Which of the following best why we see horizontal "stripes" in photographs of Jupiter and Saturn? A. There are three different color stripes corresponding to the three different types of clouds found on these planets. B. Dark stripes are those in which there is a stratosphere and light stripes are those with no stratosphere. C. The light stripes are regions of high clouds, and the dark stripes are regions where we can see down to deeper, darker clouds. D. The dark and light stripes correspond to alternating bands of different chemical composition.

C. The light stripes are regions of high clouds, and the dark stripes are regions where we can see down to deeper, darker clouds.

Which statement about motion in the universe is not true? A. Your speed of rotation around Earth's axis is faster if you live near the equator than if you live near the North Pole. B. Some stars in the Milky Way Galaxy are moving toward us and others are moving away from us. C. The mysterious dark matter is the fastest-moving material in the universe. D. Except for a few nearby galaxies, all other galaxies are moving away from us.

C. The mysterious dark matter is the fastest-moving material in the universe. This is the correct answer because the statement is not true. In fact, dark matter is thought to reside galaxies and clusters of galaxies, and hence moves with these galaxies and clusters; it does not move faster than them.

Which of the following best describes why we say that light is an electromagnetic wave? A. Light can be produced only by electric or magnetic appliances. B. Light is produced only when massive fields of electric and magnetic energy collide with one another. C. The passage of a light wave can cause electrically charged particles to move up and down. D. The term electromagnetic wave arose for historical reasons, but we now know that light has nothing to do with either electricity or magnetism.

C. The passage of a light wave can cause electrically charged particles to move up and down.

The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see? A. The two stars will appear to be touching, looking rather like a small dumbbell. B. The stars will not show up at all in your photograph. C. The photo will seem to show only one star rather than two. D. You will see two distinct stars in your photograph.

C. The photo will seem to show only one star rather than two.

Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes what the planets would look like? A. The planets range in size from about the size of a marble to the size of a baseball. They are spread out over a region about the size of a football field. B. The planets are all much smaller than the Sun and are spread out evenly over a distance about the length of a large classroom. C. The planets are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the rest planets are spread much farther apart. D. The planets are all much smaller than the Sun. Four planets are located within a few centimeters of the Sun, and four planets are located at distances ranging up to about a meter.

C. The planets are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the rest planets are spread much farther apart.

Which statement about accretion disks is not true? A. The gas in the inner parts of the disk travels faster than the gas in the outer parts of the disk. B. The gas in the inner parts of the disk is hotter than the gas in the outer parts of the disk. C. The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass. D. Accretion disks are made primarily of hydrogen and helium gas.

C. The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass. The primary factor is not mass, but rather it is whether the white dwarf is in a close binary system where gas from its companion can spill over.

Which statement about Saturn's rings is not true? A. The large gap known as the Cassini Division is shaped by an orbital resonance with the moon Mimas, which orbits well outside the rings. B. The rings are so thin that they essentially disappear from view when seen edge-on. C. The rings must look much the same today as they did shortly after Saturn formed. D. Some features of the rings are shaped by small moons that actually orbit within the ring system.

C. The rings must look much the same today as they did shortly after Saturn formed. Ring particles cannot last long compared to the age of the solar system, so the rings much change their appearance with time.

Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster? A. The question is nonsense - gas temperature cannot possibly tell us anything about mass. B. The temperature of the gas tells us the gas density, so we can use the density to determine the cluster's mass. C. The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass. D. Temperature is always directly related to mass, which is why massive objects are always hotter than less massive objects.

C. The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass.

What is the primary basis upon which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; metal)? A. The amounts of energy required to ionize various materials. B. The atomic mass numbers of various materials. C. The temperatures at which various materials will condense from gaseous form to solid form. D. The locations of various materials in the solar nebula.

C. The temperatures at which various materials will condense from gaseous form to solid form. Condensation determined the materials available in solid form in different regions of the nebula.

Scientists do not know what dark energy is, yet they still claim that it is the dominant constituent of the mass-energy of the universe. What (if any) evidence supports this claim? A. The only evidence comes from observations of white dwarf supernovae that indicate the expansion rate is accelerating. B. The claim comes from models of the Big Bang, but it is not backed up by any observational evidence. C. There are two lines of evidence: measurements of the accelerating expansion, and the universal geometry inferred from the cosmic microwave background. D. There are two lines of evidence: the fact that the universe is expanding, and the observed ratio of deuterium to hydrogen.

C. There are two lines of evidence: measurements of the accelerating expansion, and the universal geometry inferred from the cosmic microwave background. Remarkably, both lines of evidence point to the same conclusion: that dark energy is the dominant constituent of the universe, even though we do not yet have any real idea about what it is.

Although most astronomers assume dark matter really exists, there is at least one other possible explanation for the phenomena attributed to dark matter. What is it? A. There could be something wrong with our understanding of how atoms produce light. B. The so-called dark matter is really just ordinary stars that are enshrouded in clouds of dust. C. There could be something wrong or incomplete with our understanding of how gravity operates on galaxy-size scales. D. We could just be having a hard time understanding the observations because they involve very distant galaxies.

C. There could be something wrong or incomplete with our understanding of how gravity operates on galaxy-size scales.

Why do sunspots appear dark in pictures of the Sun? A. They are extremely hot and emit all their radiation as X rays rather than visible light. B. They are holes in the solar surface through which we can see through to deeper, darker layers of the Sun. C. They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere. D. They are too cold to emit any visible light.

C. They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.

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

C. They actually contain relatively little material in a gaseous state. Much more of their mass is liquid, metallic, or in strange high-pressure states that we don't naturally find on Earth.

Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond? A. They have a wavelength of two cycles per second. B. They have a frequency of 4 hertz. C. They have a frequency of 2 hertz. D. We can calculate the wavelength of the ripples from their frequency.

C. They have a frequency of 2 hertz.

Why do astronomers believe that Triton is a captured moon? A. Triton appears to be made mostly of ice. B. Triton is too large to have been formed in the "miniature solar nebula" thought to have surrounded Neptune in its very early history. C. Triton orbits Neptune in a direction opposite that of Neptune's rotation. D. Triton is very small and potato-shaped, which is common of captured moons.

C. Triton orbits Neptune in a direction opposite that of Neptune's rotation.

Which planet listed below has the most extreme seasons? A. Jupiter B. Mars C. Uranus D. Earth

C. Uranus

The Andromeda Galaxy is faintly visible to the naked eye in the constellation Andromeda. Suppose instead it were located in the same direction in space as the center of the Milky Way Galaxy (but still at its current distance). How would it appear to the eye in that case? A. It would look about the same, but would be in the constellation Sagittarius instead of Andromeda. B. It would look about the same, but it would be harder to pick out because its cloud-like appearance would make it blend in with the cloud-like appearance of the Milky Way in our sky. C. We could not see it at all. D. It would be much brighter, because it would be illuminated by the many stars in the center of our galaxy.

C. We could not see it at all. With the naked eye, we cannot see very far into the plane of the Milky Way Galaxy. Therefore, if the Andromeda direction were located directly behind the center of the Milky Way as viewed from Earth, it would not be visible to the naked eye.

How do we determine the conditions that existed in the very early universe? A. The conditions in the very early universe must have been much like those found in stars today, so we learn about them by studying stars. B. We look all the way to the cosmological horizon, where we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang. C. We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size. D. We can only guess at the conditions, since we have no way to calculate or observe what they were.

C. We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size. For estimating temperatures and densities, it's really no more difficult than calculating what happens to a gas when you compress it.

Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole surrounded by an accretion disk.) One foolhardy day, a daring individual in their space force (let's call him Major Tom) decides to become the first of his species to cross the event horizon of the black hole. To add to the drama, he decides to go in wearing only a thin space suit, which offers no shielding against radiation, no cushioning against any forces, and so on. Which of the following is most likely to kill him first (or at least to start the process of killing him first)? A. the crush of gravity at the singularity embedded within the black hole B. tidal forces due to the black hole C. X rays from the accretion disk D. the sucking force from the black hole, which will cause his head to explode

C. X rays from the accretion disk The accretion disk radiates prodigious amounts of X rays, as evidenced from the fact that we see these types of systems as X-ray binaries. They will provide enough radiation to kill him long before he begins to feel effects from tidal forces.

The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they tell us anything about where the dark matter is located within the galaxy? A. Yes, they tell us that dark matter is spread uniformly throughout the galactic disk. B. No, we cannot determine anything about the location of dark matter from the rotation curve. C. Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center. D. Yes, they tell us that dark matter is concentrated near the center of the galaxy.

C. Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center.

Assume that Hubble's constant is 22 kilometers per second per million light-years. How fast would we expect a galaxy 100 million light-years away to be moving? (Assume the motion is due only to Hubble's law.) A. toward us at 2,200 km/s B. away from us at 220 km/s C. away from us at 2,200 km/s D. away from us at 22,000 km/s

C. away from us at 2,200 km/s Multiply 22 km/s/(million light-years) × 100 million light-years = 2,200 km/s.

The intricate patterns visible in an X-ray image of the Sun generally show __________. A. a bubbling pattern on the photosphere B. structure within sunspots C. extremely hot plasma flowing along magnetic field lines D. helioseismological fluctuations

C. extremely hot plasma flowing along magnetic field lines

All the following types of objects are found almost exclusively in the disk (rather than the halo) of the Milky Way except _________. A. x-ray binaries B. young stars C. globular clusters D. high-mass, red supergiant stars

C. globular clusters Globular clusters are distributed throughout the halo, and are found in the disk only if they are currently passing through it on their orbits.

When traveling north from the United States into Canada, you'll see the North Star (Polaris) getting __________. A. brighter B. dimmer C. higher in the sky D. lower in the sky

C. higher in the sky Remember that the altitude of the north celestial pole in the local sky is equal to your latitude, so traveling north (to higher latitude) means the North Star will move higher in your sky.

If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for _________. A. the fact that our universe is expanding B. the existence of helium in the universe C. how galaxies came to exist D. the relationship between the strong and the weak force

C. how galaxies came to exist Recall that models of galaxy formation presume that they formed from "seeds" of excess density present in the early universe. If the seeds really existed, they should have left their mark as slight variations in the cosmic microwave background, and we do indeed see such variations. Thus, if we did not see the variations, we would have been forced to reconsider everything we thought we knew about galaxy formation and the history of the universe.

According to present understanding, a nova is caused by __________. A. a white dwarf that gains enough mass to exceed the 1.4-solar-mass limit B. hydrogen fusion on the surface of a neutron star C. hydrogen fusion on the surface of a white dwarf D. carbon fusion in the core of a white dwarf

C. hydrogen fusion on the surface of a white dwarf As hydrogen accretes onto a white dwarf, the temperature and pressure increase until fusion can occur.

When we see X rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole? A. spectral lines from the companion star that alternately shift to shorter and longer wavelengths B. visible and ultraviolet light from the companion star C. intense X-ray bursts D. bright X-ray emission that varies on a time scale of a few hours

C. intense X-ray bursts X-ray bursts take place on the surface of a neutron star. A black hole has no surface, and hence cannot have X-ray bursts.

Which two factors are most important to the existence of plate tectonics on Earth? A. the existence of life and oxygen in the atmosphere B. oxygen in the atmosphere and mantle convection C. mantle convection and a thin lithosphere D. Earth's liquid outer core and solid inner core

C. mantle convection and a thin lithosphere

Newton showed that Kepler's laws are __________. A. the key to proving that Earth orbits our Sun B. seriously in error C. natural consequences of the law of universal gravitation D. actually only three of seven distinct laws of planetary motion

C. natural consequences of the law of universal gravitation

Suppose it is full moon. What phase of Earth would someone on the Moon see at this time? A. full Earth B. Earth does not go through phases as seen from the Moon. C. new Earth D. first quarter Earth

C. new Earth We see full moon when the Moon is opposite the Sun in our sky. So at this time, observers on the Moon would be looking at the night side of Earth, which means they would see new Earth.

Suppose we had a device that allowed us to see Earth's interior. If we looked at a typical region of the mantle, what would we see happening? A. dense metals falling downward while low-density rock rises upward B. hot molten rock rising upward throughout the mantle and cool, solid rock falling downward C. not much - on human time scales, the mantle looks like solid rock D. a rapid, up and down churning of the material in the mantle

C. not much - on human time scales, the mantle looks like solid rock

Which two processes can generate energy to help a star maintain its internal thermal pressure? A. nuclear fusion and nuclear fission B. nuclear fission and supernova C. nuclear fusion and gravitational contraction D. nuclear fusion and supernova

C. nuclear fusion and gravitational contraction Gravitational contraction is most important before the star finishes forming, while fusion is most important during the star's lifetime.

Red and orange stars are found evenly spread throughout the galactic disk, but blue stars are typically found _________. A. in the halo B. only in the central bulge C. only in or near star-forming clouds D. also evenly spread throughout the galactic disk

C. only in or near star-forming clouds Blue stars are hot and therefore massive and therefore short-lived, which means they never have time to venture far from the places where they were born.

In any particular place on Earth, certain constellations are visible in the evening only at certain times of the year because __________. A. on any particular night, we can only see stars that are directly opposite (180 degrees away from) the Sun in the sky B. during some times of year, some constellations drop below the southern horizon C. our evening view of space depends on where Earth is located in its orbit around the Sun D. some constellations are circumpolar

C. our evening view of space depends on where Earth is located in its orbit around the Sun

Suppose that inflation did not occur. In that case, the fact that the cosmic microwave background has the same temperature in opposite directions of the sky would be considered ___________. A. surprising, because we would not expect those locations to have the same age B. natural, because quantum fluctuations in the early universe would have ensured that the whole universe had precisely the same temperature C. surprising, because those locations would never have been close enough to have any light or matter exchanged between them D. natural, because everything in the universe is naturally expected to have the same temperature

C. surprising, because those locations would never have been close enough to have any light or matter exchanged between them

If our year were twice as long (that is, if Earth took twice as many days to complete each orbit around the Sun), but Earth's rotation period and axis tilt were unchanged, then __________. A. the cycle of precession would take 13,000 years instead of 26,000 years B. stars would take twice as long to rise and set C. the four seasons would each be twice as long as they are now D. the Earth would not have seasons

C. the four seasons would each be twice as long as they are now

When you see the bright flash of a meteor, what are you actually seeing? A. emission of visible light from a particle that has not yet entered Earth's atmosphere B. the flash that occurs when a speeding rock from space hits the ground C. the glow from a pea-size particle and the surrounding air as the particle burns up in our atmosphere D. a star that has suddenly shot across the sky

C. the glow from a pea-size particle and the surrounding air as the particle burns up in our atmosphere

When we analyze whether a world is a possible home to life, the key thing we look for is __________. A. evidence of atmospheric oxygen B. surface coloration changes that could indicate vegetative growth C. the past or present existence of liquid water D. the presence of organic molecules such as amino acids

C. the past or present existence of liquid water

If we imagine the history of the universe compressed into one year, dinosaurs became extinct __________. A. about an hour ago B. about 6 months ago C. yesterday morning D. about 3 weeks ago

C. yesterday morning

Imagine another solar system, with a star of the same mass as the Sun. Suppose a planet with a mass twice that of Earth (2M Earth) orbits at a distance of 1 AU from the star. What is the orbital period of this planet? A. 2 years. B. 6 months. C. It cannot be determined from the information given. D. 1 year.

D. 1 year. The planet's mass is so small compared to the star's mass that it has essentially no effect on the planet's orbit. (We know this from Newton's version of Kepler's third law.) The fact that the planet has the same orbital distance as Earth therefore means it must have the same orbital period as Earth.

According to the Big Bang theory, how many forces - and which ones - operated in the universe during the GUT era? A. 1 force that represented the unification of all four forces that operate today B. 3 forces: gravity, the strong force, and the electroweak force C. 2 forces: the strong force and the electroweak force D. 2 forces: gravity and a single force that later became the strong, weak, and electromagnetic forces

D. 2 forces: gravity and a single force that later became the strong, weak, and electromagnetic forces The GUT era takes its name because "grand unified theories" (GUTs) are theories that attempt to unify they strong, weak, and electromagnetic forces (but do not also include gravity).

The approximate main-sequence lifetime of a star of spectral type O is __________. A. 10,000 years B. 300 million years C. 10 billion years D. 3 million years

D. 3 million years O stars are the shortest-lived of all stars, because they are the most massive and therefore the most luminous.

Which of statement below about black holes is not true? A. Although we are not 100% certain that black holes exist, we have strong observational evidence in favor of their existence. B. If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon. C. If you watch someone else fall into a black hole, you will never see him (or her) cross the event horizon; you'll only see him fade from view as the light he emits or reflects becomes more and more redshifted. D. A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star.

D. A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star. For example, a spaceship might pass quite safely by the black hole at a distance of 10,000 kilometers, but at 10,000 kilometers from the center of the main-sequence star the spaceship would be deep inside the star. (Of course, the spaceship would be destroyed long before it got that close to the star's center.)

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

D. As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.

Which of the following is not a piece of evidence supporting the idea that Europa may have a subsurface ocean? A. Europa has a magnetic field that appears to respond to Jupiter's magnetic field. B. Europa's surface shows very few impact craters. C. Photos of Europa's surface show regions that appear to consist of jumbled icebergs frozen in place. D. Astronomers have detected small lakes of liquid water on Europa's surface.

D. Astronomers have detected small lakes of liquid water on Europa's surface. There is no evidence of liquid water on Europa's surface, and even if liquid water emerged the cold temperatures would ensure that it would quickly freeze.

Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different isotopes of the same element? A. Atom 1: nucleus with 8 protons and 8 neutrons, surrounded by 8 electrons; Atom 2: nucleus with 8 protons and 8 neutrons, surrounded by 7 electrons B. Atom 1 : nucleus with 6 protons and 8 neutrons, surrounded by 6 electrons; Atom 2: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons C. Atom 1: nucleus with 4 protons and 5 neutrons, surrounded by 4 electrons; Atom 2: nucleus with 5 protons and 5 neutrons, surrounded by 4 electrons D. Atom 1: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons; Atom 2: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons

D. Atom 1: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons; Atom 2: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons They are isotopes both atoms have the same atomic number but different atomic mass numbers.

Which of the following describes a major danger of interstellar travel at near-light speed? A. Any interstellar journey will take much longer than the lives of the crew members. B. Asteroid fields floating in interstellar space will present a navigational challenge. C. Time dilation will slow the heart beats of the crew to a dangerously low rate. D. Atoms and ions in interstellar space will hit a fast-moving spacecraft like a flood of dangerous cosmic rays.

D. Atoms and ions in interstellar space will hit a fast-moving spacecraft like a flood of dangerous cosmic rays. That is, ordinary atoms and ions that are slow-moving with respect to the stars will be very fast moving as viewed from a spacecraft traveling near the speed of light.

Why do the patterns of the stars in our sky look the same from year to year? A. Because the stars in the constellations all move at the same speeds and in the same directions, so they don't change their relative positions. B. Because the stars in the constellations move so slowly --- typically about the speed of a snail --- that their motions are not noticeable. C. Because the stars in the constellations are not moving. D. Because the stars in the constellations are so far away.

D. Because the stars in the constellations are so far away.

In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why? A. Before that time, the universe was dark so there was no light to illuminate anything. B. 380,000 years after the Big Bang marks the time when stars were first born, and thus began to shine the light by which we can see the universe. C. Before that time, the universe was too crowded with stars. D. Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.

D. Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely. Until about 380,000 years into the history of the universe, hydrogen atoms were ionized and photons would scatter off electrons before they could travel very far; the universe was opaque.

Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye? A. We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky. B. Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full Moon. It would also be about as bright as the full Moon. C. Because the supernova destroys the star, Betelgeuse would suddenly disappear from view. D. Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.

D. Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime. To see why this is true, think back to the scale of our solar system (see Chapter 1) and the distances to stars. Even with a big cloud of gas expanding away from it, a star will still look like a point of light to the naked eye.

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

D. Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A. Luminosity is an intrinsic property, so two identical stars will always have the same luminosity. But apparent brightness follows an inverse square law with distance, so the fact that Star A is twice as far away makes it 2^2 = 4 times dimmer.

Suppose you are using the Doppler method to look for planets around another star. What must you do? A. Compare the brightness of the star over a period of many months or years. B. Carefully examine a single spectrum of the star. C. Carefully examine a single spectrum of an orbiting planet. D. Compare many spectra of the star taken over a period of many months or years. E. Compare many spectra of an orbiting planet taken over a period of many months or years.

D. Compare many spectra of the star taken over a period of many months or years.

Which of the following will allow you to learn something about a transiting planet's atmospheric composition? A. Use the Doppler method to study the planet throughout a cycle from one transit to the next. B. Look for slight variations in the time between transits. C. Calculate the planet's size, and then use size to infer what its atmospheric composition must be. D. Compare spectra obtained before and during an eclipse.

D. Compare spectra obtained before and during an eclipse.

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? A. Copernicus placed the Sun at the center, but did not realize that the Moon orbits the Earth. B. Copernicus misjudged the distances between the planets. C. Copernicus placed the planets in the wrong order going outward from the Sun. D. Copernicus used perfect circles for the orbits of the planets.

D. Copernicus used perfect circles for the orbits of the planets.

Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on) in a high-mass star is not true? A. As each stage ends, the core shrinks and heats further. B. Each successive stage creates an element with a higher atomic number and atomic mass number. C. As each stage ends, the reactions that occurred in previous stages continue in shells around the core. D. Each successive stage lasts for approximately the same amount of time.

D. Each successive stage lasts for approximately the same amount of time. Each successive stage is shorter and shorter.

Which of the following best describes the geological histories of the Moon and Mercury? A. Impact cratering shaped these worlds early in their histories. Then, during the past few million years, they were reshaped by episodes of volcanism and tectonics. B. All four geological processes were important in their early histories, but only impact cratering still reshapes their surfaces today. C. Impact cratering is the only major geological process that has affected their surfaces. D. Early in their histories, they suffered many impacts and experienced some volcanism and tectonics, but they now have little geological activity at all.

D. Early in their histories, they suffered many impacts and experienced some volcanism and tectonics, but they now have little geological activity at all.

Why are fossils of early life on Earth more rare than fossils of plants and animals from the past few hundred million years? A. Fossils could not form before there was oxygen in the atmosphere. B. We find fossils in sedimentary layers, and no sediments were deposited until just a few hundred million years ago. C. Life was far less abundant prior to a few hundred million years ago. D. Early organisms lacked skeletons and other hard structures that are most likely to be fossilized.

D. Early organisms lacked skeletons and other hard structures that are most likely to be fossilized. In addition, early life was microscopic, and microscopic fossils are much more difficult to find than large fossils, even when they are intact.

When we see a meteor shower, it means that __________. A. you should duck and run for cover to avoid being blasted on the head by a rock from space B. the solar wind is unusually strong C. an Earth-approaching asteroid has recently come very close to our planet D. Earth is crossing the orbit of a comet

D. Earth is crossing the orbit of a comet

Which analogy best explains why inflation predicts that the overall geometry of the observable universe should appear to be flat? A. If you stretch a wavy line infinitely, it become straight. B. No city on Earth is any more the "center" of Earth's surface than any other city. C. As a balloon expands, dots that you have drawn on it become farther apart with time. D. Earth is so big that it the part explored by an ant appears flat.

D. Earth is so big that it the part explored by an ant appears flat.

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

D. Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits

Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit? A. White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit. B. The upper limit to a white dwarf's mass is something we have learned from observations, but no one knows why this limit exists. C. White dwarfs get hotter with increasing mass, and above the 1.4-solar-mass limit they would be so hot that even their electrons would melt. D. Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit.

D. Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. No particle can move faster than the speed of light, so once the electrons get close to that speed there is a limit to how much faster they can move - and hence to how much more pressure they can exert.

Why does the Sun emit neutrinos? A. Solar flares create neutrinos with magnetic fields. B. The Sun was born with a supply of neutrinos that it gradually emits into space. 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.

Which of the following statements is not an assumption used in models of galaxy formation? A. Some regions in the universe were slightly more dense than others. B. The universe is expanding. C. The universe started out filled almost uniformly with hydrogen and helium. D. Gas contracted to form the disks of galaxies before any stars were born.

D. Gas contracted to form the disks of galaxies before any stars were born. This is not one of the starting assumptions, and probably is not even true.

If you could watch a time-lapse movie of the interstellar medium over hundreds of millions of years, what would you see? A. The entire disk of the Milky Way would pulsate in and out as it contracts to form stars and then blows out in supernovae and then contracts to form stars again and so on. B. The movie would alternate back and forth between being very bright when there is a lot of gas and very dark when there is very little gas. C. Gas that changes only in very slow and steady ways, so that the movie would in fact be quite boring. D. Gas that is often moving at high speed, particularly after one or more supernovae, and constantly changing form between molecular clouds, atomic hydrogen, and hot, ionized bubbles and superbubbles.

D. Gas that is often moving at high speed, particularly after one or more supernovae, and constantly changing form between molecular clouds, atomic hydrogen, and hot, ionized bubbles and superbubbles.

Which of the following statements is true of green grass? A. It absorbs red light and emits green light. B. It means the lawn is healthy. C. It transmits all colors of light except green. D. It absorbs red light and reflects green light.

D. It absorbs red light and reflects green light.

How does Earth's varying distance from the Sun affect our seasons? A. It is responsible for the fact that the seasons are opposite in the Northern and Southern hemispheres. B. It causes the seasons to be more extreme than they would be if the Earth's distance from the Sun were always the same. C. It makes summer warmer in the Northern Hemisphere than in the Southern Hemisphere. D. It doesn't --- Earth's orbital distance plays no significant role in the seasons.

D. It doesn't --- Earth's orbital distance plays no significant role in the seasons. The difference in distance over the course of the year is not enough to affect Earth's seasons; seasons on Earth are caused by the tilt of Earth's axis.

According to our present theory of solar system formation, which of the following best explains why the solar nebula ended up with a disk shape as it collapsed? A. The law of conservation of energy. B. The force of gravity pulled the material downward into a flat disk. C. It was fairly flat to begin with, and retained this flat shape as it collapsed. D. It flattened as a natural consequence of collisions between particles in the nebula.

D. It flattened as a natural consequence of collisions between particles in the nebula. These collisions tend to change random motions into more orderly ones.

How does a 12-month lunar calendar differ from our 12-month solar calendar? A. Its new year always occurs in February instead of on January 1. B. It does not have seasons. C. It uses a 23-hour rather than a 24-hour day. D. It has about 11 fewer days.

D. It has about 11 fewer days.

Which of the following statements best describes the size of the largest asteroid, Ceres? A. It is smaller than the jovian planets but larger than the terrestrial planets. B. It is no larger than a typical mountain on one of the terrestrial planets. C. It is about the size of a terrestrial planet. D. It is a little less than half the diameter of our Moon.

D. It is a little less than half the diameter of our Moon.

Relative to the age of the universe, how old is our solar system? A. It is between about 5% and 10% as old as the universe. B. It is about 1% as old as the universe. C. It is nearly the same age as the universe. D. It is about one-third the age of the universe.

D. It is about one-third the age of the universe. The universe is about 14 billion years old and the solar system about 4½ billion years ago, and 4½ billion years is about one-third of 14 billion years.

Which of the following statements is not true of the object known as Sgr A* in the center of our Galaxy? A. It is a source of bright radio emission. B. It is a source of X-ray emission that we have observed with telescopes in space. C. It is thought to harbor a black hole of about 4 million solar masses. D. It is by far the brightest source of visible light lying in the direction of the galactic center.

D. It is by far the brightest source of visible light lying in the direction of the galactic center.

How does the interstellar medium affect our view of most of the galaxy? A. It absorbs all wavelengths of light. B. It produces so much visible light that it blocks our view of anything beyond it. C. It has no effect on visible-light observations, but prevents us from studying the galactic center with radio waves or X rays. D. It prevents us from seeing most of the galactic disk with visible and ultraviolet light.

D. It prevents us from seeing most of the galactic disk with visible and ultraviolet light. This is true because interstellar dust absorbs visible and ultraviolet.

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. The Sun's gas is on fire like flames from wood or coal, and these flames emit visible light. C. Nuclear fusion in the Sun's core produces visible light photons. 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.

Which of the following statements about matter-antimatter engines is not true? A. Matter-antimatter reactions represent the most efficient possible reactions in terms of energy release. B. Spacecraft powered by matter-antimatter engines could probably reach speeds of more than half the speed of light. C. One of the major challenges to developing matter-antimatter engines is finding a way to store antimatter after it is produced. D. Matter-antimatter engines would be great in theory, but to date we have no evidence that antimatter even exists.

D. Matter-antimatter engines would be great in theory, but to date we have no evidence that antimatter even exists. We already produce antimatter in laboratories (particle accelerators), so there is no doubt that it exists.

Could we see a galaxy that is 20 billion light-years away? (Assume that we mean a "lookback time" of 20 billion years.) A. Yes, we have already detected galaxies at that distance. B. No, because a galaxy could not possibly be that far away. C. Yes, if we had a big enough telescope. D. No, because it would be beyond the bounds of our observable universe.

D. No, because it would be beyond the bounds of our observable universe. (The universe is about 14 billion-years old, so we cannot observe objects more than about 14 billion light-years away.)

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

D. Particles in the solar nebula were more spread out at greater distances, so that accretion took longer and there was less time to pull in gas before the solar wind cleared the nebula.

Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system? A. It is impossible to say. B. Supernovae are more common. C. They both occur in about equal numbers. D. Planetary nebula formation is more common.

D. Planetary nebula formation is more common.

Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather than some other type of star? A. Several pulsars are located within a dozen light-years of our solar system, making them useful for finding our solar system. B. Pulsars are very bright and therefore easy to find. C. We're pretty sure that aliens will have only radio telescopes and not optical telescopes, so they'll have a better chance of seeing pulsars than ordinary stars. D. Pulsars are easy to identify by their almost perfectly steady periods of pulsation.

D. Pulsars are easy to identify by their almost perfectly steady periods of pulsation. Therefore, aliens would presumably be able to realize that we'd chosen pulsars and thereby be able to interpret the map.

Which statement about pulsars is not thought to be true? A. A pulsar must have a very strong magnetic field and rotate quite rapidly. B. All pulsars are neutron stars, but not all neutron stars are pulsars. C. Pulsars are kept from collapsing by neutron degeneracy pressure. D. Pulsars can form only in close binary systems.

D. Pulsars can form only in close binary systems. Any neutron star may appear to us as a pulsar only if it has beams of radiation sweeping by us with each rotation, regardless of whether it is in a close binary system.

Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude? A. Rigel has a higher core temperature than Sirius. B. Sirius has a higher core temperature than Rigel. C. Sirius has a higher surface temperature than Rigel. D. Rigel has a higher surface temperature than Sirius.

D. Rigel has a higher surface temperature than Sirius. This is true because the spectral sequence from hot to cool is OBAFGKM, which means spectral type B is hotter than spectral type A.

If we could watch spiral arms from a telescope situated above the Milky Way over 500 million years, what would we see happen? A. The spiral arms will seem to "wind up", to wrap more and more tightly around the center of the Galaxy. B. The spiral arms will eventually dissipate and fade away, since they are a temporary phenomenon that should only last for a million years or so. C. The spiral arms will eventually unwind, as centripetal forces send the stars flying outwards into intergalactic space. D. Stars will move through the spiral arms, bunching up closer as they pass through. Young hot stars will form and die within the arms before having a chance to move out.

D. Stars will move through the spiral arms, bunching up closer as they pass through. Young hot stars will form and die within the arms before having a chance to move out. Young hot stars don't live long enough to survive until the enhanced density of gas in a spiral arm (which leads to star formation) passes by.

Why is Europa considered a good candidate for the possible existence of life? A. The Galileo spacecraft found strange seasonal changes on its surface that look like they could be due to life. B. It is located within our Sun's habitable zone. C. It has a thick atmosphere with a surface pressure greater than that on Earth. D. Strong evidence suggests that it has a deep, subsurface ocean of liquid water.

D. Strong evidence suggests that it has a deep, subsurface ocean of liquid water. Indeed, Europa likely had more ocean than Earth, and probably also has volcanic activity on its seafloor.

Uranus and Neptune have methane clouds but Jupiter and Saturn do not. Which factor explains why? A. The stronger gravity on Jupiter and Saturn pulls methane downward so that it can't form clouds. B. Jupiter and Saturn do not contain any methane gas. C. The rapid rotation of Jupiter and Saturn prevents methane clouds from forming. D. Temperatures on Jupiter and Saturn are too high for methane to condense.

D. Temperatures on Jupiter and Saturn are too high for methane to condense. But methane can condense on Uranus and Neptune because they are farther from the Sun and hence colder.

Which of the following is not a major difference between the terrestrial and jovian planets in our solar system? A. Terrestrial planets are higher in average density than jovian planets. B. Terrestrial planets orbit much closer to the Sun than jovian planets. C. Jovian planets have rings and terrestrial planets do not. D. Terrestrial planets contain large quantities of ice and jovian planets do not.

D. Terrestrial planets contain large quantities of ice and jovian planets do not.

Which of the following statements about the celestial sphere is NOT true? A. The Earth is placed at the center of the celestial sphere. B. When we look in the sky, the stars all appear to be located on the celestial sphere. C. The celestial sphere does not exist physically. D. The "celestial sphere" is another name for our universe.

D. The "celestial sphere" is another name for our universe.

Which of the following correctly compares the Sun's energy generation process to the energy generation process in human-built nuclear power plants? A. The Sun generates energy through fission while nuclear power plants generate energy through fusion. B. Both processes involve nuclear fusion, but the Sun fuses hydrogen while nuclear power plants fuse uranium. C. The Sun generates energy through nuclear reactions while nuclear power plants generate energy through chemical reactions. D. The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei.

D. The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei.

Suppose the Sun were suddenly to shrink in size but that its mass remained the same. According to the law of conservation of angular momentum, what would happen? A. The Sun's rate of rotation would slow. B. The Sun's angular size in our sky would stay the same. C. This could never happen, because it is impossible for an object to shrink in size without an outside torque. D. The Sun would rotate faster than it does now.

D. The Sun would rotate faster than it does now.

Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight? A. The ball's gravitational potential energy is greatest at the instant it returns to hit the ground. B. The ball's gravitational potential energy is always the same. C. The ball's gravitational potential energy is greatest at the instant the ball leaves your foot. D. The ball's gravitational potential energy is greatest at the instant when the ball is at its highest point.

D. The ball's gravitational potential energy is greatest at the instant when the ball is at its highest point.

How can we best observe the Sun's chromosphere and corona? A. The chromosphere and corona are both best studied with radio telescopes. B. The chromosphere and corona are both best studied with visible light. C. The chromosphere is best observed with infrared telescopes and the corona is best observed with ultraviolet telescopes. D. The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes.

D. The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes. The chromosphere is hot enough to emit mostly ultraviolet light and the corona to emit mostly X rays.

Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space? A. The cloud is cool and very dense, so that you cannot see any objects that lie behind it. B. The cloud is extremely hot. C. The cloud is visible primarily because it reflects light from nearby stars. D. The cloud is cool and lies between you and a hot star.

D. The cloud is cool and lies between you and a hot star.

Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse? A. The cloud must collide with other clouds. B. The cloud must trap most of its thermal energy. C. New dust particles must continually be made in the cloud. D. The cloud must radiate much of its thermal energy.

D. The cloud must radiate much of its thermal energy. Otherwise, the cloud would heat up, which would increase the thermal pressure and halt the gravitational collapse.

Why are there fewer large impact craters on the Earth's seafloor than on the continents? A. Erosion erases impact craters must faster on the ocean bottom than on land. B. The oceans slow large impactors and prevent them from making craters. C. Most impacts occur on the land. D. The crust on seafloors is younger than on continents, so it has had less time in which to suffer impacts.

D. The crust on seafloors is younger than on continents, so it has had less time in which to suffer impacts. Seafloor crust is continually recycled, so that the seafloor is nearly everywhere younger than about 200 million years. Therefore evidence of any earlier impacts has been erased as the seafloor crust was recycled.

The Big Bang theory seems to explain how elements were formed during the first few minutes after the Big Bang. Which hypothetical observation below (these are not real observations) would call our current theory into question? A. The discovery of a planet that with no helium in its atmosphere. B. The discovery of a star-like object made entirely of carbon and oxygen. C. The discovery of a galaxy with 27% helium by mass. D. The discovery of a galaxy with a helium abundance of only 10% by mass.

D. The discovery of a galaxy with a helium abundance of only 10% by mass. The Big Bang theory predicts that the minimum helium abundance for a galaxy would be about 25% by mass.

Which of the following statements about gamma ray bursts is not true? A. Gamma ray bursts are among the most luminous events that ever occur in the universe. B. Based on their distribution in the sky, we can rule out a connection between gamma ray bursts and X-ray binaries in the Milky Way Galaxy. C. Gamma ray bursts were originally discovered by satellites designed to look for signs of nuclear bomb tests on Earth. D. The events responsible for gamma ray bursts apparently produce only gamma rays, and no other light that we can hope to detect.

D. The events responsible for gamma ray bursts apparently produce only gamma rays, and no other light that we can hope to detect. In at least a few cases, we have detected the sources of gamma ray bursts in other wavelengths. Indeed, it was such observations that convinced astronomers that the bursts occur in distant galaxies.

Interactions among galaxies also are thought to influence a galaxy's type in at least some cases. Which of the following does not support the idea that interactions can shape galaxies? A. The presence of features such as "tails" extending out of galaxies, bridges between galaxies, and rings of stars around galaxies. B. The fact that galaxies with distorted appearances are more common at great distances than nearby. C. Computer modeling of collisions between galaxies. D. The fact that more distant galaxies have larger redshifts.

D. The fact that more distant galaxies have larger redshifts.

According to our present theory of solar system formation, which of the following statements about the growth of terrestrial and jovian planets is not true? A. Swirling disks of gas, like the solar nebula in miniature, formed around the growing jovian planets but not around the growing terrestrial planets. B. The terrestrial planets formed inside the frost line of the solar nebula and the jovian planets formed beyond it. C. Both types of planet begun with planetesimals growing through the process of accretion, but only the jovian planets were able to capture hydrogen and helium gas from the solar nebula. D. The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal.

D. The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal. The planetesimals in the outer solar system were not made only of ice: they also contained rock and metal. Remember, if it's cold enough for ices to condense from hydrogen compounds, it's certainly cold enough for rock and metal to condense as well.

Suppose Earth's axis tilt was significantly greater than its current 23.5 degrees, but Earth's rotation period and orbital period were unchanged. Which statement below would not be true? A. Summers and winters would be more severe (for example, hotter and colder, respectively) than they are now. B. The region of Earth where the Sun does not rise on the winter solstice would be larger (extending farther south) than it is now. C. Polaris would not be our North star. D. The length of each season (for example, the number of days from the summer solstice to the fall equinox) would be significantly longer than it is now.

D. The length of each season (for example, the number of days from the summer solstice to the fall equinox) would be significantly longer than it is now. The length of the seasons would be unaffected, because this is determined by Earth's orbital period.

Most of the Moon's surface is densely covered with craters, but we find relatively few craters within the lunar maria. What can we conclude? A. The maria formed within the past 1 billion years. B. The regions of the maria were hit by fewer impacts than the densely cratered regions. C. Erosion affects the maria more than it affects other regions of the Moon. D. The maria formed after the heavy bombardment ended.

D. The maria formed after the heavy bombardment ended. They contain few craters because they formed after most impacts had occurred.

Which characteristic is not generally true of a starburst galaxy? A. Supernovae occur so frequently that their effects combine to drive a galactic wind that blows material into intergalactic space. B. The observed features that cause us to classify it as a "starburst" must be only temporary phenomena in the galaxy's history. C. Its rate of star formation is many times higher than the rate of star formation in the Milky Way. D. The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center.

D. The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center. Starbursts are not related to active galactic nuclei, and it is the latter that are thought to involve supermassive black holes.

Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be different? A. The orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant. B. The rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round. C. The rotation curve would look the same with or without the presence of dark matter. D. The orbital speeds would fall off sharply with increasing distance from the galactic center.

D. The orbital speeds would fall off sharply with increasing distance from the galactic center. This is what happens to the rotation curve of objects orbiting a centralized mass, such as the planets in our solar system

You observe a star very similar to our own Sun in size and mass. This star moves very slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet? A. The planet must have a mass about the same as the mass of Jupiter. B. You do not have enough information to say anything at all about the planet. C. The planet must be farther from the star than Neptune is from the Sun. D. The planet must be closer to the star than Earth is to the Sun.

D. The planet must be closer to the star than Earth is to the Sun.

How did the Ptolemaic model explain the apparent retrograde motion of the planets? A. The model showed that apparent retrograde motion occurs as Earth passes by another planet in its orbit of the Sun. B. The planets sometimes stopped moving and then reversed to move backward along their circular orbits. C. The planets resided on giant spheres that sometimes turned clockwise and sometimes turned counterclockwise. D. The planets moved along small circles that moved on larger circles around the Earth.

D. The planets moved along small circles that moved on larger circles around the Earth.

In general, how does the size and location of a star's habitable zone depend on the star's mass? A. The smaller (less massive) the star, the larger and the closer-in the habitable zone. B. The habitable zone is always about the same size, but its location moves inward for smaller stars. C. The smaller (less massive) the star, the larger and the farther-out the habitable zone. D. The smaller (less massive) the star, the smaller and the closer-in the habitable zone.

D. The smaller (less massive) the star, the smaller and the closer-in the habitable zone.

Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude? A. The star is moving away from us. B. The star is getting colder. C. The star is getting hotter. D. The star is moving toward us.

D. The star is moving toward us.

Why are terrestrial planets denser than jovian planets? A. Actually, the jovian planets are denser than the terrestrial planets. B. The Sun's gravity gathered dense materials into the inner solar system. C. Gravity compresses terrestrial planets to a higher degree, making them denser. D. The terrestrial planets formed in the inner solar nebula, where only dense materials could condense.

D. The terrestrial planets formed in the inner solar nebula, where only dense materials could condense.

Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true? A. Shifts in the wavelengths of spectral lines compared to the wavelengths of those same lines measured in a laboratory on Earth can tell us the star's speed toward or away from us. B. We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals. C. The peak of the star's thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths. D. The total amount of light in the spectrum tells us the star's radius.

D. The total amount of light in the spectrum tells us the star's radius. We cannot measure radius from a spectrum without additional information.

If WIMPs really exist and make up most of the dark matter in galaxies, which of the following is not one of their characteristics? A. They can neither emit nor absorb light. B. They tend to orbit at large distances from the galactic center. C. They are subatomic particles. D. They travel at speeds close to the speed of light.

D. They travel at speeds close to the speed of light. If they traveled this fast, they would escape from galaxies and clusters instead of being gravitationally bound as the dark matter in galaxies must be. Indeed, it is the high speeds of neutrinos that rule them out as a major component of the dark matter in galaxies. Also, the particles are "massive" (as subatomic particles go) and therefore it would be extremely difficult to accelerate them to relativistic speeds.

Which of the following best describes the origin of ocean tides on Earth? A. Tides are caused on the side of the Earth nearest the Moon because the Moon's gravity attracts the water. B. Tides are caused by the 23.5-degree tilt of the Earth's rotational axis to the ecliptic plane. C. The Moon's gravity pulls harder on water than on land, because water is less dense than rock. D. Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth.

D. Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth.

Suppose you are facing north and you see the Big Dipper close to your northern horizon, with Polaris (and the Little Dipper) above it. Where will you see the Big Dipper in six hours? A. Still in the same place, below Polaris B. Directly above Polaris C. To the left of Polaris; that is, 90 degrees clockwise from its current position D. To the right of Polaris; that is, 90 degrees counterclockwise from its current position

D. To the right of Polaris; that is, 90 degrees counterclockwise from its current position Facing north, the sky appears to turn counterclockwise. In 6 hours, the sky will turn ¼ of the way around a full circle, so you all stars will appear to have moved 90 degrees counterclockwise around the north celestial pole.

Which of the following best explain what we think happened to outgassed water vapor on Venus? A. Water was removed from the atmosphere by chemical reactions with surface rock. B. It is frozen as water ice in craters near the poles. C. It turned into carbon dioxide by reacting with nitrogen in Venus's atmosphere. D. Ultraviolet light split the water molecules, and the hydrogen then escaped to space.

D. Ultraviolet light split the water molecules, and the hydrogen then escaped to space.

How does gravitational lensing tell us about the mass of a galaxy cluster? A. Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster. B. The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law. C. The lensing broadens spectral lines, and we can use the broadening to "weigh" the cluster. D. Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it.

D. Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it. In fact, with careful observations, we can also calculate the overall distribution of the mass within the cluster.

All the following statements are true. Which one follows directly from Kepler's third law (p 2 = a 3)? A. Venus has a thicker atmosphere than Mercury. B. Venus takes longer to rotate than it does to orbit the Sun. C. Venus is more massive than Mercury. D. Venus orbits the Sun at a slower average speed than Mercury.

D. Venus orbits the Sun at a slower average speed than Mercury. Kepler's third law tells us that orbital speed declines with distance, so Venus must orbit the Sun at a slower speed than Mercury.

Why can't current theories describe what happened during the Planck era? A. We do not understand the properties of antimatter. B. We do not know how hot or dense the universe was during that time. C. The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant. D. We do not yet have a theory that links quantum mechanics and general relativity.

D. We do not yet have a theory that links quantum mechanics and general relativity. Current understanding suggests that all four forces must have been unified at that time, but we cannot explain how they were unified until we can reconcile quantum mechanics and gravity.

Which of the following best describes the predominant scientific view of the origin of life on Earth? A. Life arose through a series of extremely unlikely chemical coincidences, making it seem almost miraculous that life ever came to exist at all. B. Life probably migrated to Earth from some other world. C. We can describe with great certainty the precise steps by which life arose on Earth. D. We may never know precisely how life arose, but current evidence suggests that life probably can arise naturally under the conditions that prevailed on the early Earth.

D. We may never know precisely how life arose, but current evidence suggests that life probably can arise naturally under the conditions that prevailed on the early Earth.

Earth is farthest from the Sun in July and closest to the Sun in January. During which Northern Hemisphere season is Earth moving fastest in its orbit? A. Summer B. Spring C. Fall D. Winter

D. Winter

Suppose you live in the United States and you see a crescent moon in your evening sky tonight. What will a friend in South America see tonight? A. Your friend will see a gibbous moon. B. Your friend will see a first quarter moon. C. Your friend won't see the Moon tonight, because it is up only in the morning. D. Your friend will also see a crescent moon.

D. Your friend will also see a crescent moon.

Suppose you find a meteorite made almost entirely of metal. According to current science, which of the following statements must be true? A. Your meteorite is a fragment of an object from the Kuiper belt. B. Radiometric dating will show the age of your meteorite to date to the formation of our solar system. C. Your meteorite was blasted off the surface of Mars by an impact. D. Your meteorite is a fragment from the core of a large asteroid that shattered in a collision.

D. Your meteorite is a fragment from the core of a large asteroid that shattered in a collision. Only a large asteroid would have undergone differentiation to make a metal core, so this must be the source of the meteorite.

In general, which type of planet would you expect to cause the largest Doppler shift in the spectrum of its star? A. a low-mass planet that is close to its star B. a massive planet that is far from its star C. a low-mass planet that is far from its star D. a massive planet that is close to its star

D. a massive planet that is close to its star

If we could see our own galaxy from 2 million light-years away, it would appear _________. A. to fill the sky with widely spaced stars B. as a faintly glowing band of light stretching all the way around the sky C. like a single, dim star D. as a flattened disk with a central bulge and spiral arms

D. as a flattened disk with a central bulge and spiral arms

The most common form of gas in the disk of the Milky Way galaxy is _________. A. gas in stellar winds B. molecular hydrogen C. gas in hot bubbles D. atomic hydrogen gas

D. atomic hydrogen gas This is gas that is too warm for molecules to form, but cool enough so the hydrogen is not ionized.

The white dwarf that remains when our Sun dies will be mostly made of _____. A. hydrogen B. neutrons C. helium D. carbon

D. carbon

Which of the following gases is not a significant ingredient of the jovian planet atmospheres? A. water B. hydrogen C. helium D. carbon dioxide

D. carbon dioxide Carbon dioxide is important in the terrestrial planet atmospheres, but not in the jovian planet atmospheres.

According to the model in which active galactic nuclei are powered by supermassive black holes, the energy released as light comes from __________. A. matter-antimatter annihilation occurring just outside the event horizon of the black hole B. jets emerging from the accretion disk C. nuclear fusion in the accretion disk surrounding the black hole D. gravitational potential energy released by matter that is falling toward the black hole

D. gravitational potential energy released by matter that is falling toward the black hole The matter loses gravitational potential energy as it falls inward.

Our Sun is considered to be a _________. A. intermediate-mass star B. brown dwarf C. high-mass star D. low-mass star

D. low-mass star

If we could put all the asteroids together, their total mass would be __________. A. about the mass of Earth B. greater than the mass of Earth but less than the mass of Jupiter C. about the mass of Mercury D. much less than the mass of any terrestrial planet

D. much less than the mass of any terrestrial planet

Galileo challenged the idea that objects in the heavens were perfect by __________. A. showing that heavy objects fall at the same rate as lighter objects B. inventing the telescope C. proving Kepler's laws were correct D. observing sunspots on the Sun and mountains on the Moon

D. observing sunspots on the Sun and mountains on the Moon

The transit method allows us in principle to find planets around __________. A. only stars located within about 100 light-years of Earth B. all stars that have planets of any kind C. only stars of about the same mass and size as our Sun D. only a small fraction of stars that have planets

D. only a small fraction of stars that have planets We can see transits only if the planetary orbits are nearly precisely edge-on as viewed from Earth, which means that most planetary systems cannot be detected through transits. The Kepler mission overcomes this limitation by studying a large number of stars (about 150,000).

To calculate the masses of stars in a binary system, we must measure their __________. A. luminosities and distance from Earth B. spectral types and distance from Earth C. absolute magnitudes and luminosities D. orbital period and average orbital distance

D. orbital period and average orbital distance We can then apply Newton's version of Kepler's third law to find the sum of their masses.

Gaps in the asteroid belt (often called Kirkwood gaps) are caused by __________. A. tidal forces from Jupiter B. the competing gravitational tugs of Mars and Jupiter C. tidal forces from the Sun D. orbital resonances with Jupiter

D. orbital resonances with Jupiter

Very few of the known extrasolar planets have sizes as small as Earth. The most likely reason for this fact is that __________. A. small planets are usually made of materials that cannot be detected B. small planets probably orbit too far from their stars to have been detected yet C. small planets are extremely rare D. small planets are more difficult to detect than larger planets

D. small planets are more difficult to detect than larger planets

Observations indicated that over billions of years, galaxies in general tend to change from __________. A. larger and redder to smaller and bluer B. smaller and redder to larger and bluer C. larger and bluer to smaller and redder D. smaller and bluer to larger and redder

D. smaller and bluer to larger and redder

The more massive a white dwarf, the __________. A. larger its radius B. higher its temperature C. higher its luminosity D. smaller its radius

D. smaller its radius

What does cosmological redshift do to light? A. makes it brighter B. makes all light infrared C. makes it slow down D. stretches its wavelength

D. stretches its wavelength The effect is essentially the same that occurs with a redshift from the Doppler effect, but the underlying cause is different.

Based on current evidence, a supercluster is most likely to have formed in regions of space where __________. A. there was an excess concentration of hydrogen gas when the universe was very young B. supermassive black holes were present in the very early universe C. the acceleration of the expansion was proceeding faster than elsewhere D. the density of dark matter was slightly higher than average when the universe was very young

D. the density of dark matter was slightly higher than average when the universe was very young Dark matter is presumed to dominate the mass of the universe, so its gravity governs the formation of large-scale structure.

We can study how galaxies evolve because __________. A. we can watch as they interact in real time B. galaxies are transparent to visible light C. we are really smart astronomers D. the farther away we look, the further back in time we see

D. the farther away we look, the further back in time we see

Angular momentum plays an important role in star formation. Which of the following characteristics of a protostellar system is probably not strongly affected by the star's angular momentum? A. the strength of protostellar winds B. the formation of a protostellar disk C. the existence of protostellar jets D. the onset of core hydrogen fusion

D. the onset of core hydrogen fusion The time to onset of hydrogen burning is mainly affected by a protostar's mass, not by its rotation (or angular momentum).

The total number of stars in the observable universe is about _________. A. the same as the number of atoms that make up the Earth B. 100 billion C. the same as the number of grains of sand in a school sandbox D. the same as the number of grains of sand on all the beaches on Earth

D. the same as the number of grains of sand on all the beaches on Earth

Spiral arms appear bright because ________. A. they are the only places where we find stars within the disk of the galaxy B. they contain more molecular clouds than other parts of the disk C. they contain far more stars than other parts of the galactic disk D. they contain more hot young stars than other parts of the disk

D. they contain more hot young stars than other parts of the disk This is true because spiral arms have enhanced density that leads to more star formation, and young hot stars don't live long enough to move far from the places where they are born.

It's 6 am and the Moon is at its highest point in your sky (crossing the meridian). What is the Moon's phase? A. first quarter B. new C. full D. third quarter

D. third quarter Third quarter moon rises around midnight, reaches its highest point around 6am, and sets around noon. That is why you can see the third-quarter moon in the morning sky.

Suppose that the universe were infinite in both extent and age. In that case, we would expect the night sky to be ___________. A. much larger B. filled with about 1,000 times as many stars C. expanding at a more rapid rate D. uniformly bright

D. uniformly bright

Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case __________. A. we are seeing Galaxy 1 as it looked at a later time in the history of the universe than Galaxy 2 B. Galaxy 2 must be twice as old as Galaxy 1 C. Galaxy 1 must be twice as big as Galaxy 2 D. we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2

D. we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2

Suppose it turns out that one in 1 million stars has a planet that at some point in its history is home to an advanced civilization. Then the total number of civilizations that have arisen in our galaxy would be closest to __________. A. 1 B. 10 C. 100 D. 10,000 E. 100,000 F. 1,000

E. 100,000 The number of stars in the Milky Way Galaxy is at least about 100 billion, and 100 billion divided by 1 million = 100,000.

Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude? A. Star X is hotter than Star Y. B. Star Y is moving away from us faster than Star X. C. Star X is moving away from us and Star Y is moving toward us. D. Star X is coming toward us faster than Star Y. E. Star X is moving away from us faster than Star Y.

E. Star X is moving away from us faster than Star Y.

Which of the following is always true about images captured with X-ray telescopes? A. They always are made with adaptive optics. B. They always have very high angular resolution. C. They are always very pretty. D. They show us light with extremely long wavelengths compared to the wavelengths of visible light. E. They are always shown with colors that are not the true colors of the objects that were photographed.

E. They are always shown with colors that are not the true colors of the objects that were photographed. "True colors" make sense only for visible light, not X rays.

Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole surrounded by an accretion disk.) Through a bizarre (and scientifically unexplainable) fluctuation in the space-time continuum, a copy of a book from that civilization arrives on your desk; it is entitled Iguoonos: How We Evolved. In the first chapter, you learn that these beings evolved from organisms that lived 5 billion years ago. Which of the following statements should you expect to find as you continue to read this book? A. As a result of traumatic experiences to their evolutionary ancestors, they dislike television. B. They believe that the presence of two stars in their system was critical to their evolution. C. Their immediate ancestors were chimpanzees. D. They evolved from primitive wormlike creatures that had 13 legs, 4 eyes, and bald heads, thus explaining why such critters are now considered a spectacular delicacy. E. They evolved on a different planet in a different star system, and moved to their current location.

E. They evolved on a different planet in a different star system, and moved to their current location. The total lifetime of the massive stars in their system is only a few million years. If they evolved 5 billion years ago, then they must have moved to their current location.

All stars are born with the same basic composition, yet stars can differ greatly in appearance. Which two basic factors are most important in determining the current appearance of a star? A. its luminosity and its stage of life B. its age and its location in the galaxy C. its apparent brightness and its luminosity D. its mass and its surface temperature E. its mass and its stage of life

E. its mass and its stage of life Mass determines the star's life progression, so the star's current place along that progression depends on its current stage of life.