Exam 3 Spring 2000 Practice Test 1
Many of these questions will appear in their original form, as given here,
but most will not. You are forewarned not to simply memorize the answers.
1) How does the interstellar medium obscure our view of most of the galaxy?
A) It reflects most light from far distances of the galaxy away from our line of sight.
2) Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by
B) It absorbs visible, ultraviolet, and some infrared light.
C) It absorbs all wavelengths of light.
D) It produces so much visible light that it is opaque and blocks our view of anything beyond it.
E) All of the above.
A) mapping the distribution of stars in the galaxy.
3) Where are most heavy elements made?
B) looking at the shape of the "milky band" across the sky.
C) mapping the distribution of globular clusters in the galaxy.
D) mapping the distribution of gas clouds in the spiral arms.
E) looking at other nearby spiral galaxies.
A) in stars and supernovae
4) What produces the 21-cm line that we use to map out the Milky Way Galaxy?
B) in the interstellar medium
C) in the Big Bang, when the universe first began
D) none of the above
E) all of the above
A) atomic hydrogen
5) Compared with our Sun, most stars in the halo are
B) molecular hydrogen
C) ionized hydrogen
E) carbon monoxide
A) young, red, and dim and have fewer heavy elements.
6) What kinds of objects lie in the halo of our galaxy?
B) old, red, and dim and have much more heavy element material.
C) young, blue, and bright and have much more heavy element material.
D) old, red, and bright and have fewer heavy elements.
E) old, red, and dim and have fewer heavy elements.
A) globular clusters
7) What kinds of objects lie in the disk of our galaxy?
B) gas and dust
C) open clusters
D) O and B stars
E) all of the above
A) open clusters
8) Compared with stars in the disk, orbits of stars in the halo
B) old K and M stars
C) gas and dust
D) O and B stars
E) all of the above
A) are elliptical, with random orientation.
9) Why do we believe 90% of the mass of the Milky Way is in the form of dark matter?
B) are relatively uniform to each other.
C) are elliptical but orbiting in the same direction.
D) do not have to be around the galactic center.
E) do not have to pass through the plane of the galaxy.
A) Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo.
10) Which constellation lies in the direction toward the galactic center?
B) Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material.
C) 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, suggesting that the halo is full of dark matter.
D) 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.
11) How do we learn about what is going on in the center of our own galaxy (the Milky Way)?
E) the Big Dipper
A) The gas and dust in the Milky Way prevent any type of direct observation of the galactic center, but theoretical models allow us to predict what is happening there.
12) What evidence supports the theory that there is a black hole at the center of our galaxy?
B) We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.
C) We have learned it only recently, thanks to the great photographs obtained by the Hubble Space Telescope.
D) We must look at the centers of other galaxies and hope that ours is just like others.
A) We can see gas falling into an accretion disk and central mass at the center of our galaxy.
13) 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?
B) 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.
C) We observe an extremely bright X-ray source at the center of our galaxy.
D) We observe a large, dark object that absorbs all light at the center of our galaxy.
E) All of the above.
A) the one that is closest to us
14) Which of the following types of galaxies are most spherical in shape?
B) the one that is reddest in color
C) the one that is bluest in color
D) the one that is farthest away
E) the one that appears smallest in size
A) irregulars B) spirals C) lenticulars D) ellipticals
15) Which of the following types of galaxies are reddest in color?
A) spirals B) lenticulars C) ellipticals D) irregulars
16) Which types of galaxies have a clearly defined disk component?
A) spirals only
17) The disk component of a spiral galaxy includes which of the following parts?
B) irregulars only
C) ellipticals only
D) lenticulars only
E) spirals and lenticulars
A) halo B) spiral arms C) bulge D) All of the above
18) What is the major difference between an elliptical galaxy and a spiral galaxy?
A) Elliptical galaxies are not as big as spiral galaxies.
19) Most large galaxies in the universe are
B) An elliptical galaxy lacks a disk component.
C) A spiral galaxy contains mostly younger stars.
D) There are no dwarf spiral galaxies, but there are dwarf ellipticals.
E) A spiral galaxy has a spherical halo.
A) abnormal. B) irregular.
C) elliptical. D) spiral or lenticular.
20) Which of the following types of galaxies are most commonly found in large clusters?
A) spirals B) lenticulars C) ellipticals D) irregulars
21) Why are Cepheid variables important?
A) Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future.
22) What is a standard candle?
B) Cepheid variables are stars that vary in brightness because they harbor a black hole.
C) Cepheids are a type of young galaxy that helps us understand how galaxies form.
D) 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.
A) any star for which we know the exact apparent brightness
23) How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?
B) an object for which we are likely to know the true luminosity
C) a long, tapered candle that lights easily
D) a class of objects in astronomy that all have exactly the same luminosity
E) an object for which we can easily measure the apparent brightness
A) Since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way.
24) What is Hubble's law?
B) He used main-sequence fitting to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
C) He measured the stellar parallax of the Cepheid in Andromeda, was able to determine the distance to it, and showed that it was far outside the Milky Way Galaxy.
D) From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
E) There are no Cepheids in the Milky Way, so his discovery proved that it had to be in another galaxy.
A) The longer the time period between peaks in brightness, the greater the luminosity of the Cepheid variable star.
25) What is the primary practical difficulty that limits the use of Hubble's law for measuring distances?
B) The recession velocity of a galaxy is directly proportional to its distance from us.
C) The faster a spiral galaxy's rotation speed, the less luminous it is.
D) The recession velocity of a galaxy is inversely proportional to its distance from us.
E) The faster a spiral galaxy's rotation speed, the more luminous it is.
A) We do not know Hubble's constant very accurately yet.
26) What is the most accurate way to determine the distance to a nearby star?
B) Redshifts of galaxies are difficult to measure.
C) The motion of the Earth relative to the Milky Way is difficult to account for.
D) Hubble's law is only useful theoretically; it is difficult to use in practice.
E) The recession velocities of distant galaxies are so great that they are hard to measure.
A) radar ranging
27) What is the most accurate way to determine the distance to a nearby galaxy?
B) Hubble's law
C) main-sequence fitting
D) using Cepheid variables
E) stellar parallax
A) radar ranging
28) Dr. X believes that the Hubble constant is 55 km/s/Mpc. Dr. Y believes it is 80 km/s/Mpc. Which statement below automatically follows?
B) Hubble's law
C) stellar parallax
D) using Cepheid variables
E) the Tully-Fisher relation
A) Dr. X believes that the universe is older than Dr. Y believes, based on the value of the Hubble constant.
29) Dr. Smith believes that the Hubble constant is 70 km/s/Mpc. Dr. Jones believes it is 50 km/s/Mpc. Which statement below automatically follows?
B) Dr. X believes that the universe has a much higher density than Dr. Y believes.
C) Dr. X believes that the universe will someday stop expanding, while Dr. Y believes it will expand forever.
D) Dr. X believes that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a slower speed than Dr. Y believes.
E) Dr. X believes that the universe is expanding, but Dr. Y does not.
A) Dr. Smith believes that the universe is younger than Dr. Jones believes, based on the value of the Hubble constant.
30) Recall that Hubble's law is written v = Hod, where
v is the recession velocity of a galaxy located a distance d away from us, and Ho is Hubble's constant. Suppose Ho = 70 km/s/Mpc. How fast would a galaxy located 500 megaparsecs distant be receding from us?
B) Dr. Smith believes that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a faster speed than Dr. Jones believes.
C) Dr. Smith believes that the universe is expanding, but Dr. Jones does not.
D) Dr. Smith believes that the universe will someday stop expanding, while Dr. Jones believes it will expand forever.
E) Dr. Smith believes that the universe is older than Dr. Jones believes, based on the value of the Hubble constant.
A) 7000 Mpc/s
31) How do observations of distant galaxies help us learn about galaxy evolution?
B) 9 km/s
C) 35,000 km/s
D) 7500 km/s
E) 0.70 times the speed of light
A) We can observe the evolution of a single galaxy over time.
32) What is a quasar?
B) We can observe two galaxies merging and what the result is, helping us learn how mergers affect evolution.
C) We can observe the birth of galaxies.
D) We can see what our galaxy used to look like and therefore theorize about the physical processes that led to its current appearance.
E) Observations at different distances show galaxies of different ages and therefore different stages of evolution.
A) the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
33) The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
B) a starlike object that actually represents a bright patch of gas in the Milky Way
C) a specialized astronomical instrument for observing distant stars.
D) another name for very bright stars of spectral type O
E) a very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster
A) Active galactic nuclei can form only at large distances from the Milky Way.
34) Why should galaxy collisions have been more common in the past than they are today?
B) Active galactic nuclei tend to become less active as they age.
C) Massive 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.
A) Galaxies were closer together in the past because the universe was smaller.
35) What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
B) Galaxies were much bigger in the past since they had not contracted completely.
C) Galaxies were more active in the past and therefore would have collided with each other more frequently.
D) Galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars and light.
E) Galaxy collisions shouldn't have been more common in the past than they are now.
A) the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies
36) Which of the following is not a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around massive black holes?
B) observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
C) observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies
D) observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy
E) all of the above
A) Observed radiation from the galactic center varies significantly in brightness in times as short as a few days.
37) How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
B) Infrared observations show that many stars are forming near the centers of active galaxies.
C) Radio observations sometimes show long jets of material extending millions of light-years out from the galactic center.
D) The total amount of radiation coming from the galactic center is, in some cases, comparable to the amount of radiation put out by 10 billion or more ordinary stars.
E) Spectral lines from the galactic center indicate that clouds of gas are orbiting a central object at very high speed.
A) by matter-antimatter annihilation near a central black hole
38) What evidence suggests that the Milky Way contains dark matter?
B) by nuclear fusion near a central black hole
C) by magnetic fields that trap and accelerate charged particles, which then radiate high amounts of energy
D) by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter
E) by matter that has been converted to pure energy being shot out as jets by a central black hole
A) When we observe in different wavelengths, such as infrared or radio, we see objects that don't appear in visible-light observations.
39) Gravitational lensing occurs when
B) We see many lanes of dark material blocking out the light of stars behind them along the band of the Milky Way.
C) When we look at the galactic center, we are able to observe a large black hole that is composed of dark matter.
D) 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.
E) We see many dark voids between the stars in the halo of the Milky Way.
A) massive objects cause more distant objects to appear much larger than they should and we can observe the distant objects with better resolution.
40) Why isn't space expanding within systems such as our solar system or the Milky Way?
B) telescope lenses are distorted by gravity.
C) dark matter builds up in a particular region of space, leading to a very dense region and an extremely high mass-to-light ratio.
D) massive objects bend light beams that are passing nearby.
A) We are so close to these systems that we don't observe their expansion.
41) What are peculiar velocities?
B) The universe is not old enough yet for these objects to begin their expansion.
C) Hubble's law of expansion applies only to the space between galaxies.
D) Their gravity is strong enough to hold them together against the expansion of the universe.
A) velocities directly along our line of sight
42) Which of the following has your "address" in the correct order?
B) velocities of distant objects that are not caused by the expansion of the universe
C) velocities caused by the expansion of the universe
D) velocities that we cannot explain by only the force of gravity
E) velocities perpendicular to our line of sight
A) you, Earth, solar system, Local Group, Milky Way, Local Supercluster
43) What do we mean when we say that the universe is expanding?
B) you, Earth, solar system, Local Group, Local Supercluster, Milky Way
C) you, Earth, Local Group, Local Supercluster, solar system, Milky Way
D) you, Earth, solar system, Milky Way, Local Supercluster, Local Group
E) you, Earth, solar system, Milky Way, Local Group, Local Supercluster
A) The statement is not meant to be literal; rather, it means that our knowledge of the universe is growing.
44) The Earth is made mostly of metals and rocks. Where did this material come from?
B) Individual galaxies are gradually growing in size.
C) Average distances are increasing between star systems within galaxies.
D) Average distances are increasing between galaxies.
E) Everything in the universe is gradually growing in size.
A) It was made by nuclear fission of uranium and other radioactive materials.
45) Why does Carl Sagan say that we are star stuff?
B) It was produced by nuclear fusion in stars.
C) It was produced in the Big Bang.
D) It was created by chemical reactions in interstellar space.
E) It was made by our Sun.
A) Cosmic rays reaching the Earth from distant astronomical sources may be one source of mutations that help evolution along.
46) How are galaxies important to our existence?
B) The composition of most stars (mostly hydrogen and helium) is about the same as the composition of our bodies.
C) Nearly every atom from which we are made once (before the solar system formed) was inside of a star.
D) Sagan thought that all of us have the potential to be movie (or TV) stars like he was.
E) Nearly every atom from which we are made was once inside our star, the Sun.
A) Without galaxies, the universe could not be expanding.
47) Suppose 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?
B) Without galaxies, there could not have been a Big Bang.
C) Galaxies prevent planets from leaving their orbits around stars; e.g., our galaxy prevents the Earth from leaving its orbit of the Sun.
D) Galaxies provide the gravity that prevents us from falling off the Earth.
E) Galaxies recycle heavy elements produced in stars into future generations of stars.
A) the one that is bluest in color
48) The age of the universe is
B) the one that is farthest away
C) the one that appears smallest in size
D) the one that is reddest in color
E) the one that is closest to us
A) between 100 million and 160 million years.
49) Which of the following statements does not use the term light-year in an appropriate way?
B) between 1 billion and 1.6 billion years.
C) between 100 billion and 160 billion years.
D) between 10 million and 16 million years.
E) between 10 billion and 16 billion years.
A) It will take me light-years to complete this homework assignment.
50) About where is our solar system located within the Milky Way Galaxy?
B) A light-year is about 10 trillion kilometers.
C) It will take the Voyager spacecraft about 20,000 years to travel just 1 light-year.
D) It's about 4 light-years from here to Alpha Centauri.
E) The Milky Way Galaxy is about 100,000 light-years in diameter.
A) about two-thirds of the way from the center of the galaxy to the outskirts of the galactic disk
51) On the scale of the cosmic calendar, in which the history of the universe is compressed to 1 year, how long has human civilization (i.e., since ancient Egypt) existed?
B) in the halo of the galaxy above the galactic disk
C) near the far outskirts of the galactic disk
D) about 10 percent of the way from the center of the galaxy to the outskirts of the galactic disk
E) at the center of the galaxy
A) about a month
52) From the fact that virtually every galaxy is moving away from us and more distant galaxies are moving away from us at a faster rate than closer ones, we conclude that
B) a few hours
C) less than a millionth of a second
D) a few seconds
E) about half the year
A) the universe is shrinking.
53) By studying distant galaxies in the 1920s, Hubble made the following important discovery that led us to conclude that the universe is expanding:
B) the Milky Way Galaxy is expanding.
C) the farthest galaxies will eventually be moving faster than the speed of light.
D) the universe is expanding.
E) we are located at the center of the universe.
A) All galaxies outside the Local Group are moving away from us, and all are moving away at nearly the same speed.
54) Imagine that we put a raisin cake into the oven, with each raisin separated from the others by 1 cm. An hour later, we take it out and the distances between raisins are 3 cm. If you lived in one of the raisins and watched the other raisins as the cake expanded, which of the following would you conclude?
B) All galaxies outside the Local Group are moving away from us, and the farther away they are, the faster they're going.
C) All galaxies outside the Local Group are orbiting the Local Group.
D) All galaxies were born at the same time, and all will die at the same time.
E) All galaxies contain billions of stars, and all galaxies have spiral shapes.
A) All raisins would be moving away from you at the same speed.
B) It depends: If you lived in a raisin near the left side of the cake, you'd see other raisins moving away from you, but they'd be coming toward you if you lived in a raisin near the right side of the cake.
C) More distant raisins would be moving away from you more slowly.
D) More distant raisins would be moving away from you faster.