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219 Cards in this Set
- Front
- Back
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What is the DIAMETER of the DISK of the Milky Way? |
100,000 light-years |
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What is the THICKNESS of the DISK of the Milky Way? |
1,000 light-years |
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What kinds of objects lie in the halo of our galaxy? |
globular clusters |
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What kinds of objects lie in the disk of our galaxy? |
Open clusters, O and B stars, old K and M stars, gas and dust All of the above |
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Which of the following comprise the oldest members of the Milky Way? |
globular clusters |
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What makes up the interstellar medium? |
gas and dust |
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If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in? |
Warm, rarefied clouds of atomic hydrogen |
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How does the interstellar medium obscure our view of most of the galaxy? |
It absorbs visible, ultraviolet and some infrared light |
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How can we see through the interstellar medium? |
We can see through interstellar medium by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves |
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Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by... |
Mapping the distribution of globular clusters in the galaxy |
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Approximately how far is the Sun from the center of the galaxy? |
27,000 light-years |
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What do astronomers consider heavy elements? |
All elements besides hydrogen and helium |
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Where are most heavy elements made? |
Heavy elements are made in stars and supernovae |
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Why are we unlikely to find Earth-like planets around halo stars in the Galaxy? |
Halo stars formed in an environment where there were few heavy elements to create rocky planets. |
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How are interstellar bubbles made? |
By winds of massive stars and supernovae |
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What is a superbubble? |
A very low-density region of interstellar space, formed by the merger of several bubbles |
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Sound waves in space... |
travel must faster than sound on Earth but have such a low density that they are inaudible |
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What is a shock front? |
a wave of pressure that moves faster than the speed of sound |
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What are cosmic rays? |
cosmic rays are subatomic particles that travel close to the speed of light |
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What can cause a galactic fountain? |
multiple supernovae occurring together |
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What is the galactic fountain model? |
The theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk |
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What is the most common form of gas in the interstellar medium? |
atomic hydrogen |
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What produces the 21-cm line that we use to map out the Milky Way Galaxy? |
atomic hydrogen |
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Where do most dust grains form? |
in winds of red giant stars |
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Suppose you read somewhere that 10 percent of the matter in the Milky Way is in the form of dust grains. Should you be surprised? If so, why? |
The 10 percent figure cannot be correct, because dust grains are solid but only about 2 percent of the matter in our galaxy is made of anything besides hydrogen and helium. |
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The image of our galaxy in radio emission from CO, mapping the distribution of molecular clouds, is closest to the image of our galaxy in |
infrared emission from interstellar dust grains |
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Compared with our Sun, most stars in the halo are... |
old, red and dim and have fewer heavy elements |
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Compared with stars in the disk, orbits of stars in the halo... |
are elliptical, with random orientation |
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Approximately how long does it take the Sun to orbit the Milky Way Galaxy? |
230 million years |
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Where does most star formation occur in the Milky Way Galaxy? |
most star formation occurs in the spiral arms of our galaxy |
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How do we know that spheroidal stars are older, on average, than disk stars? |
There are no blue spheroid stars |
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Which of the following statements about globular clusters is false? |
Globular cluster ages increase with distance from the Milky Way |
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Which of the following statements about the disk of the Milky Way is false? |
Disk stars are all younger than 5 billion years |
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Which of the following statements about halo stars is false? |
Halo stars are made entirely of hydrogen and helium with no heavy elements |
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What evidence suggests that the protogalactic cloud that formed the Milky Way resulted from several collisions among smaller clouds? |
Halo stars differ in age and heavy-element content, but these variations do not seem to depend on the stars' distance from the galactic cloud. |
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Which constellation lies in the direction toward the galactic center? |
Sagittarius |
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How do we learn about what is going on in the center of our own galaxy (the Milky Way)? |
We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected. |
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Which of the following does not accurately describe what we observe toward the Galactic center? |
At optical wavelengths, we see a cluster of old, red stars |
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What evidence supports the theory that there is a black hole at the center of our galaxy? |
The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across. |
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What is a SgrA*? |
A SgrA* is a source of bright radio emission in the center of our galaxy |
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What evidence do we have that the spheroid population of stars are older than other stars in our galaxy? |
They have a smaller proportion of heavy elements |
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Based on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately... |
100 Billion |
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Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest? |
The one that is farthest away |
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Which of the following types of galaxies are most spherical in shape? |
Ellipticals |
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Which of the following types of galaxies are reddest in color? |
Ellipticals |
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Which of the following statements about galaxies is true? |
Small galaxies outnumber large galaxies but large galaxies produce the most of the light in the universe. |
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Which types of galaxies have a clearly defined spheroidal component? |
all but irregulars |
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Which types of galaxies have a clearly defined disk component? |
spirals and lenticulars |
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Compared to spiral galaxies, elliptical galaxies are... |
redder and rounder |
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The disk component of a spiral galaxy includes which of the following parts? |
spiral arms |
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How does a lenticular galaxy differ from a normal spiral galaxy? |
It has NO spiral arms |
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What is the major difference between an elliptical galaxy and a spiral galaxy? |
An elliptical galaxy lacks a disk component |
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Most large galaxies in the universe are... |
Spiral and lenticular |
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Which of the following types of galaxies are most commonly found in large clusters? |
ellipticals |
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Approximately how many stars does a dwarf elliptical galaxy have? |
LESS than a BILLION |
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Which of the following is true about irregular galaxies? |
They were more common when the universe was younger |
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Why are Cepheid variables important? |
Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements. |
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What is a standard candle? |
An object for which we are likely to know the true luminosity |
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Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars? |
It is close enough to us that the distance to the cluster stars can be found by stellar parallax |
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How did Edwin Hubble measure the distance to the Andromeda Galaxy? |
He applied the period-luminosity relation to Cepheid vairables |
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How was Edwin Hubble able to use his discovery of Cepheid in Andromeda to prove the "spiral nebulae" were actually entire galaxies? |
From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that is was far outside the Milky Way Galaxy. |
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What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe? |
Velocity and distance |
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What is Hubble's Law? |
The recession velocity of a galaxy is directly proportional to its distance from us. |
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Which of the following is a consequence of Hubble's law? |
The more distant a galaxy is from us, the faster it moves away from us. |
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What is the primary practical difficulty that limits the use of Hubble's Law for measuring distances? |
We do not know Hubble's constant very accurately yet. |
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White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which? |
White-dwarf supernovae occur ONLY among YOUNG and EXTREMELY bright stars |
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What makes a white-dwarf supernovae good standard candles? |
They are very bright, so they can be used to determine the distances to galaxies billions of light-years away AND they should all have approximately the same luminosity. BOTH A and B |
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What is the most accurate way to determine the distance to a nearby STAR? |
Stellar parallax |
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What is the most accurate way to determine the distance to a nearby GALAXY? |
using Cepheid variables |
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What is the most accurate way to determine the distance to a very distant irregular galaxy? |
Using white-dwarf supernova as a standard candle |
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Which of the following sequences lists the method for determining the distance in the correct order from NEAREST to FARTHEST? |
Parallax, Main-sequence fitting, Cepheid variables, Hubble's Law. P M H |
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Dr. X believes that the Hubble constant is H0 = 55 km/s/Mpc. Dr. Y believes it is H0 = 80 km/s/Mcp. Which statemet below automatically follows? |
Dr. X believes that the universe is OLDER than Dr. Y believes. |
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Dr. Smith believes that the Hubble constant is H0= 70 km/s/Mcp. Dr. Jones believes it is H0= 50 Km/s/Mcp. Which statement below automatically follows? |
Dr. Smith believes that the universe is YOUNGER than Dr. Jones believes. |
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Recall that Hubble's Law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0=65 Km/s/Mcp. How fast would a galaxy located 500 megaparsecs distant be receding from us? |
32,500 km/s |
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Hubble's "constant" is constant in... |
SPACE |
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Based on current estimates of value of Hubble's constant, how old is the universe? |
Between 12 and 16 billion years. |
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Why can't we see past the cosmological horizon? |
Beyond the cosmological horizon, we are looking BACK to a time before the universe had formed. |
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What does the equivalent of an H-R diagram for galaxies, plotting luminosity versus color, show? |
TWO clumps, ONE BLUE with relatively LOW luminosity, ONE RED with relatively HIGH luminosity. |
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How do observations of distant galaxies help us learn about galaxy evolution? |
Observations at different distances show galaxies of different ages and THEREFORE different stages of evolution |
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Why are telescopes sometimes called "time machines"? |
telescopes are sometimes called "time machines" because observations of distant objects reveal them as they were in the past |
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I observe a galaxy that is 100 million light-years away: what do I see? |
The light from the galaxy as it was 100 million years ago and it is REDSHIFTED |
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Which of the following gives the two main assumptions of theoretical models of galaxy evolution? |
Hydrogen and Helium filled all of space, and certain regions of the universe were slightly denser than others |
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Which of the following processes slowed the collapse of protogalactic clouds? |
the shock waves from the exploding supernovae of the earliest stars |
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Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy? |
a DENSE cloud with very LITTLE angular momentum |
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Why is a dense cloud more likely to produce and elliptical galaxy than a spiral galaxy? |
the HIGHER gas density forms stars for efficiently, so all the gas is converted into stars before a disk can form |
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What evidence supports the theory that elliptical galaxies come from denser clouds? |
Elliptical galaxies at HIGH redshifts LACK young, blue stars. |
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If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about... |
3 m |
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Why should galaxy collisions have been more common in the past than they are today? |
Galaxies were closer together in the past because the universe was SMALLER |
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What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy? |
- Observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies. - The fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies - Observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy. - Observations of giant elliptical galaxies at the center of dense clusters that may have gown by consuming other galaxies ALL OF THE ABOVE |
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Which of the following is NOT a strong argument for the theory that some large elliptical galaxies formed as the result of galaxy collision? |
Galaxy collisions are common and most galaxies in the universe and elliptical <-- NOT A STRONG ARGUMENT |
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What is a central dominant galaxy? |
A GIANT elliptical galaxy at the CENTER of a DENSE CLUSTER |
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How many more stars does a starburst galaxy form, in one year, than the Milky Way? |
about a hundred |
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Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution? |
Such galaxies produce SO MUCH LIGHT that they would have consumed all their gas long ago if they had always been forming stars at this high rate. |
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Starburst galaxies produce most of their light in the wavelength range of... |
the infrared |
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What evidence suggests that small galaxies in our Local Group have undergone TWO or MORE starbursts in the past? |
We see small galaxies in which many stars have one age and many others have another age that is billions of years older. |
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In the 1960s, Maarten Schmidt, determined that quasars were very distant object by... |
determining their REDSHIFTS |
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What is a quasar? |
the extremely bright center of a distant galaxy, thought to be powered by a MASSIVE BLACK HOLE |
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Which of the following is NOT true of quasars? |
Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time. |
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Which of the following is evidence for supermassive black holes in active galaxies? |
- the discovery of powerful jets coming from a compact core - rapid changes in the luminosity of the galaxy nucleus - quasars emit approximately equal power at all wavelengths from infrared to gamma rays - very high speed orbital motions around galactic nuclei ALL OF THE ABOVE |
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The most active galactic nuclei are usually found at LARGE distances from us; relatively few galaxies have active galactic nuclei. What does this IMPLY? |
Active galactic nuclei tend to BECOME LESS ACTIVE as they age |
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What is a galactic wind? |
Hot gas erupting into intergalactic space from a LARGE SUPERBUBBLE |
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If an object doubles its luminosity in 10 hours, how large can the emitting source of light be? |
about 10 light-hours across |
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Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude? |
the X ray source is NO MORE than a FEW light-days in diameter. |
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Which os the following is NOT a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around massive black holes? |
Infrared observations show that many stars are forming NEAR the centers of active galaxies |
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How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced? |
by GRAVITY, which converts potential energy of matter falling toward a central black holes into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter. |
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Where are the X rays produced that are emitted by quasars and other active galactic nuclei? |
in HOT GAS in an accretion disk around a central black hole |
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How do we know that there are intergalactic clouds between a distant quasar and us? |
We see hydrogen absorption lines at REDSHIFTS SMALLER than that of the quasar |
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What are the typical features seen in quasar absorption lines of intergalactic clouds? |
The hydrogen line is WIDER and lines from heavy elements are WEAKER at higher redshifts |
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Which of the following CANNOT be true of the very first stars formed in the universe? |
they may have had ROCKY PLANETS around them |
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All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe? |
They are more common at very great distances. |
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To date, physicists have investigated the behavior of matter and energy at temperatures as high as those that existed in the universe as far back as _____ after the Big Bang. |
10^ -10 second |
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How long after the Big Bang was the Planck time, before which our current theories are completely unable to describe conditions of the universe? |
10^ -43 second |
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The Planck era refers to the time period... |
BEFORE the Planck time |
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Why can't current theories describe what happened during the Planck era? |
We DO NOT yet have a theory that links quantum mechanics and general relativity |
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A GUT (grand unified theory) refers to theories that... |
UNIFY the STRONG FORCE AND the ELECTROMAGNETIC and WEAK FORCES |
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When we say that the electromagnetic and weak forces "freeze out" from the electroweak force at 10^-10 seconds after the Big Bang, we mean that... |
prior to this time the electromagnetic and weak forces maintained a single identity, but they possessed separate identities following this time. |
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How many forces operated in the universe during the GUT era? |
TWO, Gravity and the GUT force |
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Which forces have physicists shown to be the same force under conditions of very high temperature or energy, as confirmed by experiments in particle accelerators? |
the ELECTROMAGNETIC and WEAK forces |
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What do we mean by inflation? |
a sudden expansion of the universe after the strong force froze out from the GUT force |
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(From a science quiz that appeared in the weekly magazine The Economist.) Economic history is easier to write than the history of the universe. Nevertheless, most cosmologists now think that when the universe was formed, |
Most cosmologists now think that when the universe was formed first there was a Big Bang, then inflation (of space) caused recession (of all matter, away from the Big Bang) |
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Why might inflation have occurred at the end of the GUT era? |
An enormous amount of energy was released when the strong force froze out from the GUT force |
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What direct evidence do we have that the weak and electromagnetic forces were once unified as a single electroweak force? |
Particle accelerators on Earth can reach energies equivalent to the high temperatures of this era and have produced particles predicted by the electroweak theory. |
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What happened to the quarks that existed freely during the particle era? |
They combined in groups to make protons, neutrons and their antiparticles. |
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Approximately how long did the era of nucleosynthesis last? |
5 minutes |
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What kinds of atomic nuclei formed during the era of nucleosynthesis? |
HYDROGEN and HELIUM and trace amounts of DEUTERIUM and LITHIUM |
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Why is the era of nucleosynthesis so important in determining the chemical composition of the universe? |
Except for the small amounts of matter produced later by stars, the chemical composition of the universe is the SAME now as at the end of the era of nucleosynthesis. |
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Why did the era of nuclei end when the universe was about 300,000 years old? |
The universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form. |
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Evidence that the cosmic background radiation really is remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang and comparing these predictions with observations. Four of the five statements below are real. Which one is fictitious? |
The cosmic background radiation is expected to contain SPECTRAL LINES of hydrogen and helium, and it does. |
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Which of the following statements about the cosmic background radiation is NOT true? |
It is the RESULT of a mixture of radiation from many independent sources, such as stars and galaxies. |
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Where do the photons in the cosmic background radiation originate? |
the END of the ERA OF NUCLEI |
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Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum? |
The background radiation came from the HEAT of the universe, with a peak corresponding to the temperature of the universe. |
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Why do we expect the cosmic background radiation to be almost, but not quite, the same in all direction? |
The overall structure of the universe if very UNIFORM, but the universe must have contained some regions of HIGHER DENSITY in order for galaxies to form. |
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Helium originates from... |
the BIG BANG with a SMALL contribution from STELLAR NUCLEOSYNTHESIS |
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What are the two key observational facts that led to widespread acceptance of the Big Bang model? |
the COSMIC BACKGROUND RADIATION and the HIGH HELIUM content of the universe |
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Why do we think tiny quantum ripples should have been present in the very early universe? |
QUANTUM MECHANICS requires that the energy fields at any point in space be continually fluctuating as a result of the uncertainty principle. |
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What is postulated to have caused a sudden inflation of the early universe? |
the "freezing out" of the STRONG FORCE from the GUT force |
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Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question? |
WHY IS THE SKY DARK AT NIGHT? |
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You find yourself in a place that looks (except for your own presence) perfectly symmetrical. There is no way to distinguish one place from another, and all forces are one. With this perfect symmetry, there is no obvious way to define the flow of time. Where are you? |
You are in the early universe BEFORE the Planck time. |
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You are in a place that is extremely hot and dense, making you feel quite sweat and claustrophobic. You can't see far because your surroundings are opaque to light. Around you, nuclear fusion is converting carbon into oxygen and other elements. Where are you? |
You are in the CENTER of a MASSIVE star NEAR THE END OF ITS LIFE |
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You are on the surface of an object, and you have a fairly clear view out into space. It might be very nice, except for one major drawback: You are very squashed. Also, light you observe from distant objects is apparently slightly blueshifted (compared to what it normally looks like.) The surface of the object is composed primarily of carbon and oxygen, and the horizon distance is about the same as that on Earth. By observing the stellar background for a few weeks, you realize that there are several planets orbiting your object. Where are you? |
You are on the surface of a WHITE DWARF |
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It sure is bright everywhere; you've been able to travel around a bit, and it's clear that you are not a star. Yet it is as bright as looking directly at the Sun. In your extensive travels through your current surroundings, you cannot find a single neutral atom anywhere, nor can you find a nucleus besides hydrogen or helium. And, white it is hot (a few thousand degrees Kelvin), it is nowhere near the temperature needed for nuclear fusion. Where are you? |
You are IN THE UNIVERSE during its FIRST 300,000 years. |
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You are feeling like spaghetti. Although normally only about 2 meters tall, you are now about 25 meters long. (How fortunate, if painful, that the being has arranged for your body to become elastic enough so that it is not ripped apart under these conditions.) As you look up over your head, you see things moving pretty quickly in the universe - but that lasts only for a brief instant, and then all contact with the universe is lost. Where are you? |
You are crossing the event horizon of a BLACK HOLE. |
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You are once again in a hot, dense place. You are surrounded by protons and neutrons, some rapidly fusing into helium. You notice that your surroundings are cooling (good, because it's really hot!) and rapidly dropping in density. Within about 3 minutes, the fusion reactions stop. Where are you? |
You are in the EARLY universe DURING THE ERA OF NUCLEOSYNTHESIS |
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At last you are in a place where the heat and high density are no longer bothering you. However, although the density if very low, the gas around you is extremely high in temperature. In fact, the temperature is so high that it is emitting lots of X rays, which are creating cancer-causing mutations in your body at a rapid rate. Well, at least the view is great! There are no stars anywhere within about 10,000 light-years of you, but at slightly greater distances your sky is brightened by many beautiful, star-filled structures, some with majestic spiral shapes. Where are you? |
You are in intergalactic space within a rich cluster of thousands of galaxies. |
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At last, someplace fairly comfortable. Very weak gravity is holding you to the surface of the small object on which you sit. Your object is apparently moving away from a star, perhaps one that is orbits with a period of thousands of years. Around you, geysers are sprouting gas into space. Looking back along the object's orbit, you see particles of dust that the geysers apparently blew off the object when it was nearer to the star that it is now leaving behind. You conclude that the geysers were recently much more active but are now settling down into a quiescent state that may last for millennia. You also soon realize that your are closer to home than your have been in all your previous journeys. Perhaps if your can somehow find a small rocket, a heat shield, and a good parachute, you can escape and head home for your final exam. Where are you? |
You are on COMET Hale-Bopp, circa May 1997. |
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Which of the following observations is NOT a piece of evidence supporting the Big Bang theory? |
Relative motions of galaxies in the Local Group |
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Why do we call dark matter "dark matter"? |
It emits NO or very LITLE RADIATION of any wavelength |
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What is meant by "dark energy"? |
the agent causing the universal EXPANSION to accelerate |
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Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter? |
The orbital speeds of stars far from the galactic center are surprisingly HIGH, suggesting that these stars are feeling gravitational effects from unseen matter in the HALO. |
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How do we know that there is so much more mass in the halo of our galaxy than in the disk? |
STARS in the outskirts of the Milky Way orbit the galaxy at much HIGHER speeds than we would expect if all the mass were concentrated in the disk. |
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What evidence suggests that the Milky Way contains dark matter? |
We observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that we can see. |
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If there is no dark matter in the Milky Way Galaxy, what is the best alternative explanation for the observations? |
Our understanding of gravity is not correct for galaxy-size scales. |
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How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected? |
Through observations of the 2 cm line of atomic hydrogen |
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The distribution of the dark matter in a spiral galaxy is... |
Approximately spherical and about TEN TIMES the size of the galaxy halo. |
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How do we determine the amount of dark matter in elliptical galaxies? |
We measure the speeds of stars at different radii from the galactic center and determine how much mass is interior to the orbit. |
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When we see that a spectral line of a galaxy is broadened, that is, spanning a range of wavelengths, we conclude that... |
There are different Doppler shifts among the individual stars in the galaxy. |
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A large mass-to-light ratio for a galaxy indicates that... |
ON AVERAGE, each solar mass of matter in the galaxy emits less light than our Sun. |
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What is the mass-to-light ratio for the inner region of the Milky Way Galaxy, in units of solar masses per solar luminosity? |
6 |
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Compared to the central regions of spiral galaxies, we expect elliptical galaxies to have... |
HIGHER mass-to-light ratios because stars in elliptical galaxies are DIMMER than those in spirals. |
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If a galaxy's overall mass-to-light ratio is 100 solar masses per solar luminosity, and its stars account for only 5 solar masses per solar luminosity, how much of the galaxies mass must be dark matter? |
95 percent |
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Which of the following methods used to determine the mass of a cluster does NOT depend of Newton's law of gravity? |
measuring the amount of DISTORTION caused by a GRAVITATIONAL lens |
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Why wasn't the intracluster medium in galaxy clusters discovered until the 1960s? |
The medium emits X rays, which were blocked by the Earth's atmosphere and require X-ray satellites in space in order to be observed. |
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Which of the following statements about rich clusters of galaxies (those with thousands of galaxies) is NOT true? |
Galaxies in the central regions are predominately spirals, while elliptical galaxies roam the outskirts. FALSE |
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Gravitational lensing occurs when |
Massive objects bend light beams that are passing nearby |
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Which of the following is NOT evidence for dark matter? |
The expansion of the universe |
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Which of the following particles are baryons? |
PROTONS |
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Which of the following is an example of baryonic matter? |
YOU |
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Measuring the amount of deuterium in the universe allows us to set a limit on |
the DENSITY of ordinary (baryonic) matter in the universe |
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Based on current evidence concerning the amount of deuterium in the universe, we can conclude that |
the DENSITY of ordinary (baryonic) matter is BETWEEN 1 percent and 10 percent of the critical density |
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What do we mean when we say that a particle is a weakly interacting particle? |
It interacts only through WEAK FORCE and the FORCE OF GRAVITY |
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Why can't the dark matter in galaxies be made of neutrinos? |
Neutrinos travel at extremely HIGH SPEEDS and can escape a galaxy's gravitational pull. |
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Which of the following are candidates for dark matter? |
- brown dwarfs - Jupiter-size objects - WIMPs - faint red stars ALL OF THE ABOVE |
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Why do we expect WIMPs to be distributed throughout galactic halos, rather than settled into a disk? |
Since they do not interact with electromagnetic force, they do not feel friction or drag and hence do not contract with the rest of the protogalactic cloud. |
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Why isn't space expanding within systems such as our solar system or the Milky Way? |
Their gravity is STRONG enough to hold them together against the expansion of the universe. |
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What are peculiar velocities? |
velocities of distant objects that are NOT caused by the expansion of the universe. |
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What do peculiar velocities reveal? |
the DISTRIBUTION of dark matter in large-scale structures |
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How do astronomers create three-dimensional maps of the universe? |
by using the POSITION of the sky and the REDSHIFT to determine a distance along the line of sight |
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What does the universe look like on very large scales? |
Galaxies appear to be DISTRIBUTED in CHAINS AND SHEETS that surround great voids. |
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What fraction of the mass needed to halt expansion is known to exist in the form of visible mass in the universe? |
1 percent |
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Based on inventoried matter in the universe, including dark matter known to exist in galaxies and clusters, the actual density of the universe if what fraction of the critical density? |
26 percent |
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If all the "dark matter" in the universe were to be, somehow, instantaneously removed, which of the following would NOT happen? |
The solar system would FLY apart |
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Which model of the universe gives the youngest age for its present size |
a RECOLLAPSING universe |
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What is the ultimate fate of an open universe? |
All matter DECAYS to a LOW-DENSITY sea of photons and subatomic particles. |
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Recent measurements of the expansion rate of the universe reveal that the expansion rate of the universe is doing something astronomers did not expect. What is that? |
The measurements show that the EXPANSION is ACCELERATING, rather than slowing under the influence of gravity. |
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What is the evidence for an accelerating universe? |
White-dwarf supernovae are SLIGHTLY DIMMER than expected for a coasting universe. |
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What might be causing the universe to accelerate? |
WE DON'T KNOW! - but we call it "dark energy" |
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What is Einstein's cosmological constant? |
A REPULSIVE force that counteracts gravity and was introduced to allow for static universe |
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What is NOT a main source of evidence for the existence of dark matter? |
MASSIVE BLUE stars |
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The earliest evidence for life on Earth dates to... |
about 3.8 BILLION years ago |
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Which living organisms most resemble the common ancestor for all life according to genetic testing? |
ORGANISMS living DEEP IN THE OCEANS around seafloor volcanic vents and in hot springs |
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When did oxygen being to accumulate in the atmosphere? |
about 2 BILLION years ago |
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Which of the following statements about ozone (in Earth's atmosphere) is NOT true? |
The presence of ozone was crucial to the origin of life. |
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Why didn't oxygen begin to accumulate in the atmosphere until approximately 1.5 billion years AFTER life appeared on Earth? |
Oxygen produced by life was removed from the atmosphere by oxidation reactions with surface rocks. |
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Which of the following causes mutations in living organisms? |
ULTRAVIOLET and TOXIC CHEMICALS |
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What was the Cambrian explosion? |
a DRAMATIC diversification of life that began about 540 million years ago |
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When did the extinction of the dinosaurs occur? |
65 |
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What is absolutely NECESSARY for living organisms to survive? |
Energy |
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Where have scientists begun a concerted search for life outside of Earth? |
Mars |
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The only place outside of Earth where there is irrefutable evidence for (ancient, mircobial) life is... |
None of the above - There is NO irrefutable evidence for life beyond Earth. |
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The analysis of Martian rocks on Earth show that they CONTAIN... |
Tantalizing but unconfirmed hints of life. |
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After Mars, the next most likely candidates for life in the solar system are... |
the large moon of the jovian planets |
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How does the Kepler mission plan to detect Earth-like planets around other stars? |
by observing the slight DOP in brightness of the central star as the planet transits |
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Which of the following gases, which we might be able to detect in infrared spectra, would be a strong indicator of life on another planet? |
ozone |
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Why do some scientists think that Jupiter's existence may have been critical for life to evolve on Earth? |
It KICKED OUT many comets from the inner solar system through gravitational encounters, thus liming the number of objects that could potentially hit the inner planets. |
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Which of the following is the most important for maintaining a stable climate on Earth over the time it took for large organisms to evolve? |
plate tectonics |
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Why do some scientists say that the Moon may have been important for the evolution of human life? |
It stabilized Earth's axis tilt and prevented large climate changes |
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What defines habitable zone around a star? |
the REGION around a star where LIQUED WATER can potentially exist on planetary surfaces |
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In the equation Number of Civilization = Np x f life x f civilization x f now, What do we mean by f now? |
The fraction of planets with civilizations on which the civilizations exist now. |
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In the following statements best reflects our current knowledge about the term f life in the equation: Number of Civilization = Np x f life x f civilization x f now |
The value of f life is between 0 and 100 percent |
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At present, what is the primary way that the search for extraterrestrial intelligence (SETI) is carried out? |
by using radio telescopes to search for signals from extraterrestrial civilizations |
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In 1974, a radio message was sent out from the Arecibo observatory in Puerto Rico. How far has it gotten, approximately? |
just a miniscule fraction of the distance across the Milky Way. |
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At about what fraction of the speed of light do today's spacecraft travel? |
1/10,000 |
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The Voyager I and II spacecraft visited the jovian planets in the 1980s. When will they reach the distance of our nearest stars? |
About A HUNDRED THOUSAND years from now. |
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Which of the following describes a major danger of interstellar travel at near light speed? |
Atoms and ions in interstellar space will hit a fast-moving spacecraft like a flood of dangerous cosmic rays. |
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What type of rocket engine is used by the Space Shuttle? |
a chemical rocket |
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Which of the following statements about matter-antimatter engines is NOT true? |
Matter-antimatter engines would be great in theory, but to date we have no evidence that antimatter even exists. |
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Which of the following best explains why an interstellar ramjet could, in theory, achieve continuous acceleration? |
It collects its fuels at it goes, rather than having to carry the weight of fuel along with it. |
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If we develop spacecraft that can take humans to nearby solar systems at a few percent of the speed of light, how long would it be before we could conceivably populate all habitable planets in the entire Milky Way? |
a FEW MILLION YEARS |
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Which of the following is NOT considered a likely solution to the question of why we are not currently aware of galactic civilization? |
The galactic civilization probably is undetectable to us because it makes use of technologies that do not obey the known laws of physics. |
