Astro Final Exam

10. What do most astronomers now think explains why active galaxies are so energetic?

A. An actively accreting supermassive black hole.

3. Why are astronomers much more interested in the luminosity of a star than its apparent brightness?

A. Because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth.

18. What is the difference between an emission nebula and a reflection nebula?

A. Emission nebulae give off their own light; reflection nebulae reflect the light of nearby stars. B. Generally, emission nebulae appear red, and reflection nebulae look blue. C. In emission nebulae, gas atoms emit light; in reflection nebulae, dust particles reflect light. D. All of the above.

23. Why does a high mass star evolve differently than a low mass star?

A. It can burn more fuels because its core can get hotter.

15. Where in the Sun does fusion of hydrogen occur?

A. Only in the core.

2. Our Milky Way Galaxy is what type of galaxy?

A. Spiral

5. Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?

A. They are (for galaxies) very close to us, so they are easy to study.

8. Which of the following statements about open clusters of stars is FALSE?

A. They typically contain more mass than any other type of cluster.

15. Which of the following objects is considered useful to astronomers as a "standard candle" for determining distances?

A. Type Ia supernovae.

21. Although centuries ago, astronomers thought that a nova was a "new star," appearing for the first time in the heavens, today we know that it is

A. a binary star system in which one star is a white dwarf, and mass is being transferred to it.

9. A type of star cluster that contains mostly very old stars is

A. a globular cluster.

6. A star that is cool and very luminous must have

A. a very large radius.

23. When astronomers have examined rich clusters of galaxies with their instruments, they have found that these clusters

A. are more likely to contain giant elliptical galaxies than poor clusters.

24. Solar wind particles can be captured by the Earth's magnetosphere. When these particles spiral down along the magnetic field into the atmosphere, they are responsible for

A. aurora (northern and southern lights).

22. The Local Group

A. contains three large spiral galaxies and a couple dozen smaller galaxies. B. is a poor cluster.C. is the galaxy cluster to which the Milky Way belongs. D. is a rich cluster. E. is all of the above except D.

7. When great currents of hot material rise inside the Sun (and cooler material sinks downward), energy is being transferred what process?

A. convection

26. When a high mass star's core collapses the star _________.

A. explodes as a supernova. B. may become a neutron star. C. may become a black hole. D. All of the above.

15. The red color we see on a lot of photographs of nebulae comes from which element?

A. hydrogen

7. The Population I stars in the Milky Way Galaxy

A. include the Sun. B. generally contain a greater percentage of heavier elements than Population II stars. C. are generally found in the disk of the Galaxy. D. all of the above.

3. Astronomers think the Milky Way has spiral arms because

A. radio maps show that gas clouds are distributed in the disk with a spiral pattern. B. young, very luminous stars and star forming regions outline spiral arms. D. Only A and B are correct.

5. Stars have dark lines in their spectra because

A. the cooler atoms in their surface layers absorb the radiation at some wavelengths.

20. A white dwarf forms when

A. the shell of a planetary nebula expands and dissipates, leaving behind the dead core of a red giant.

8. After several decades of observation, astronomers have concluded that quasars are

A. very powerful and compact sources of energy at the centers of distant galaxies.

14. When astronomers discuss a nebula, what are they talking about?

B. A giant cloud of gas and dust between or among the stars.

3. Which type of galaxy is observed to contain mostly older stars?

B. Elliptical

15. Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?

B. Fusing hydrogen into helium in their cores.

10. If you want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look?

B. In a globular cluster high above the Galaxy's disk.

16. What brings a star to the end of its life?

B. It runs out of fuels it can "burn."

11. How are globular clusters distributed in our Milky Way Galaxy?

B. Mostly in a large spherical halo surrounding the flat disk of the Galaxy.

13. What powers the Sun?

B. Nuclear fusion of hydrogen into helium.

14. When a star has stopped contracting and settled down, where is it in the HR diagram?

B. On the main sequence.

8. You are out on the beach, enjoying the warm sunshine with friends. As you glance up at the Sun (only briefly we hope), the part of the Sun that you can see directly is called its

B. Photosphere

6. When energy is first produced deep in the core of the star, that energy moves outward mostly by what process?

B. Radiation

12. Which of the following is a way for astronomers to learn more about the interior of the Sun?

B. Study the oscillations on the Sun's surface.

18. What is the best reason astronomers have come up with to explain why sunspots are cooler and look darker?

B. Sunspots are places where the strong magnetic fields in the Sun resist the upward motion of bubbling hot gases from underneath.

20. Which of the following is NOT part of the growing chain of evidence that makes many astronomers suspect there is a black hole at the very center of the Milky Way Galaxy?

B. The Hubble Space Telescope has shown us a visible-light image of an accretion disk at the center of the Galaxy.

29. What is a black hole?

B. The collapsed core of a very massive star which has such an intense gravitational force that not even light can escape it.

5. Although it hasn't been observed (yet), why do astronomers think that Milky Way may contain "dark" material?

B. The galaxy's gravity seems too big for the mass astronomers can see.

30. Why do astronomers think that some of the x-ray sources they observe are associated with black holes rather than neutron stars in orbit around a normal star?

B. The mass of the unseen object inferred from its orbital motion is too large to be a neutron star.

21. What leads astronomers to conclude that the proto-galactic cloud (the cloud from which our Galaxy formed) was roughly spherical?

B. The oldest stars in the Galaxy (Population II stars, globular clusters) form a spherical halo around the Galaxy; they outline the original shape of the cloud that gave the Galaxy birth.

17. Why do sunspots appear dark?

B. They are cooler than the surrounding gas (although still very hot compared to Earth temperatures).

27. Why are supernova explosions important for our existence?

B. They liberate from the star's core the heavy elements of which we and Earth are made.

12. Which of the following statements about dark matter in galaxies is FALSE?

B. While the dark matter cannot be observed with our present-day instruments, we still have a pretty good idea what it consist of.

19. Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?

B. You must take a spectrum of the galaxy and measure the red-shift.

9. We think of the photosphere as the "surface" of the Sun because

B. above the photosphere light is no longer scattered but travels in a straight line. C. the photosphere is the part of the Sun we see (with appropriate eye protection). D. Both B and C

1. A star's parallax can reveal its distance. Stars with larger parallaxes are _______.

B. closer

21. Astronomers now realize that active regions on the Sun are connected with

B. loops of magnetic field emerging from the surface of the Sun.

10. Cooler, less luminous main sequence stars have

B. lower masses.

17. According to Hubble's Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as Galaxy A, then Galaxy B will

B. move away from us three times faster than A.

1. One way astronomers deduce that the Milky Way has a disk is that they

B. see far more stars along the band of the Milky Way than in other directions.

20. How long is it between peaks in the number of sunspots?

C. 11 years

19. What do astronomers think is at the center of the Milky Way?

C. A black hole the mass of a few million Suns

16. Where does the energy pouring out of the Sun come from ultimately?

C. A little bit of mass is lost in each fusion reaction and is turned into energy; the Sun is losing mass.

9. What is the main sequence?

C. An approximately straight line on the H-R diagram along which 90% of stars lies.

25. Coronal Mass Ejections from the Sun have many serious effects on or near the Earth. Which of the following is NOT one of these effects?

C. Causing huge cyclones around the equator of the Earth.

13. Even with the best and largest telescopes, we can't see all the stars in the Milky Way Galaxy, even though these same telescopes can show us other galaxies. Why is that?

C. Dust in the space between stars builds up over large distances and blocks the light of stars behind the dustier parts of the Milky Way.

13. One of the main projects being carried out by the Hubble Space Telescope is to measure the distances of galaxies located in groups dozens of millions of lightyears away. What method do astronomers use with the HST to find such distances?

C. Finding Cepheid variables and measuring their periods.

9. When quasars "shine" (in visible light and other kinds of radiation) with a lot of energy, where (what location) does this huge amount of energy come from?

C. From an accretion disk around a supermassive black hole.

18. When the core of a star reaches a temperature of about 100 million degrees (K), something new happens in the core. What is this new event?

C. Helium fusion begins, creating carbon.

1. The most common element in the Sun is

C. Hydrogen

6. Where would you look for the youngest stars in the Milky Way Galaxy?

C. In the disk.

13. What makes a star stop contracting?

C. It gets hot enough that its pressure builds up.

4. What holds the Sun together?

C. Its enormous gravitational force.

12. What makes a gas cloud contract to form stars?

C. Its gravity draws it inward.

17. Given the presence of dust throughout the disk of the Milky Way Galaxy, what is the best technique for learning about more distant regions of our galaxy's disk?

C. Look for radiation at long wavelengths, for example in the infrared or radio region of the spectrum.

24. What makes a high-mass star's core collapse?

C. Massive stars develop iron cores that cannot fuse anymore, so the core collapses under gravity.

3. The material inside the Sun is in the form of a

C. Plasma

1. Galaxies come in three main types which are

C. Spiral, elliptical, and irregular

22. Which statement about the Sun's rotation is TRUE?

C. The Sun rotates at different rates at different latitudes on the Sun.

23. What mechanisms do astronomers believe is responsible for making the Sun's outer atmosphere so much hotter than its photosphere?

C. The Sun's magnetic field interacting with the charged particles that make up the atmosphere.

19. Why does the number of sunspots change over time?

C. The Sun's magnetic field strengthens and weakens.

2. Suppose two stars have the same apparent brightness as viewed from Earth, but one star is much further away than the other. What can we infer about the luminosity of the stars?

C. The further star has a higher luminosity than the closer star.

4. Which of the following is NOT a characteristic of a spiral galaxy?

C. When we take spectra of its stars, they have far less of the heavier elements than the Sun.

14. According to the formula E=mc2,

C. a little bit of mass can be converted into a substantial amount of energy.

2. The location of Earth in the Milky Way Galaxy is

C. a little less than 30,000 light years from the center.

19. A planetary nebula is

C. a shell of gas ejected from a star late in its life.

11. The Sun's chromosphere and corona were discovered

C. during total eclipses of the Sun.

25. After the core of a massive star becomes a neutron star, the rest of the star's material

C. explodes outward as a supernova

12. Astronomers use the term interstellar matter to refer to

C. gas and dust that lies between stars.

10. The granulation pattern that astronomers have observed on the surface of the Sun tells us that

C. hot material must be rising from the Sun's hotter interior.

8. The H-R diagram is a plot of stars'

C. luminosity vs. temperature.

7. A binary star is a pair of stars that orbit around each other. By detecting this orbital motion, and using Kepler's Laws and the Law of Gravitation, one can directly measure the stars'

C. masses.

4. The spectral class of a star is most closely related to its

C. temperature.

28. On an H-R diagram of a cluster of stars, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age?

C. the point on the main sequence where stars begin to "turn off" and move toward the red giant region.

22. In a Type Ia supernova, the cause of the violent outburst is

C. the transfer of so much mass from a companion star that a white dwarf goes "over the limit" and collapses, causing an enormous amount of sudden fusion.

16. The reason type Ia supernovae are useful to astronomers for determining distances to other galaxies is that

C. they are very bright, and generally reach the same peak luminosity.

17. What kind of object does a main sequence star become on first using up its core hydrogen?

D. A red giant.

6. Which of the following statements about the different types (shapes) of galaxies is correct?

D. Collisions and mergers between galaxies can sometimes change a galaxy's type.

14. What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

D. Finding the red-shift and using Hubble's Law.

5. The Sun is supported against the crushing force of its own gravity by

D. Gas pressure.

16. Which of the following is NOT a way that dust in interstellar matter affects star light?

D. Giving off x-rays from hot gas surrounding the dust cloud.

20. If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look?

D. In a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away.

11. From what do stars form?

D. Interstellar clouds.

21. Which of the following does NOT happen when two galaxies collide?

D. Many of the stars in one galaxy collide with the stars in the other.

18. Why is the use of Hubble's Law to measure distances to galaxies so important to astronomers?

D. Most galaxies are so far away, the only way to get distances to them is to use Hubble's Law.

22. Which of the following is evidence that the formation process of our Galaxy may have included collisions with smaller neighbor galaxies?

D. The observation of long moving streams of stars that continue to orbit through our Galaxy's halo.

7. If quasars often resemble stars, what was it about them that so surprised astronomers when they were discovered?

D. Their spectral lines were at first hard to recognize and turned out to have large red-shifts.

11. Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?

D. There must be a great deal of invisible dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there.

25. Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is

D. about 13.8 billion years.

24. What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?

D. galaxy groups are organized into huge filaments with great voids between them -- something like the structure one would see taking a cross-section of some soap bubbles.

2. As astronomers have learned more about the structure of the Sun, they have found that it

D. is made entirely of hot gas.

4. Astronomers have measured the Milky Way's mass by

D. observing its gravitational attraction on matter in and near it.