Term
| The overall result of the proton-proton chain is |
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Definition
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Term
| Why does the Sun emit neutrinos |
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Definition
| Fusion in the Sun's core creates neutrinos as a byproduct |
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Term
| The Sun's average surface (photosphere) temperature is about ______. |
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Definition
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Term
| The Sun's surface seethes and churns with a bubbling pattern. Why? |
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Definition
| We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface |
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Term
| How can we best observe the Sun's chromosphere and corona |
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Definition
| The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes |
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Term
| Satellites in low-Earth orbits are more likely to crash to Earth during the solar maximum periods of the sunspot cycle because ______. |
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Definition
| Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits |
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Term
| Suppose that, for some unknown reason, the core of the Sun suddenly became hotter and the rate of nuclear fusion thereby increased. What would happen next? |
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Definition
| The core would expand, reducing the pressure and temperature, and the rate of fusion would decrease until it returned to its original level |
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Term
| Which of the following best explains why nuclear fusion requires bringing nuclei extremely close together? |
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Definition
| 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. |
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Term
| Which of the following best describes the current status of our understanding of the solar neutrino problem? |
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Definition
| Experimental evidence suggests that solar neutrinos can change from electron neutrinos to other types of neutrinos during their journey to Earth. If confirmed, the solar neutrino problem appears to be solved |
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Term
| The intricate patterns visible in an X-ray image of the Sun generally show ______. |
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Definition
| extremely hot plasma flowing along magnetic field lines |
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Term
| What do we mean when we say that the Sun is in gravitational equilibrium? |
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Definition
| There is a balance within the Sun between the outward push of pressure and the inward pull of gravity |
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Term
| Which of the following correctly compares the Sun's energy generation process to the energy generation process in human-built nuclear power plants? |
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Definition
| The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei |
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Term
| Which of the following is the best answer to the question "Why does the Sun shine?" |
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Definition
| 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. |
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Term
| All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the innate characteristics of a star? |
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Definition
| Its mass and its stage of life |
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Term
| Every second, the Sun converts 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons ______. |
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Definition
| are converted to an amount of energy equal to 4 million tons times the speed of light squared |
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Term
| When is/was gravitational contraction an important energy generation mechanism for the Sun? |
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Definition
| It was important when the Sun was forming from a shrinking interstellar cloud of gas. |
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Term
| Why do sunspots appear dark in pictures of the Sun? |
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Definition
| They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere |
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Term
| 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? |
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Definition
| It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this. |
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Term
| How does the Sun's mass compare to Earth's mass? |
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Definition
| The Sun's mass is about 300,000 times the mass of the Earth. |
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Term
| Based on the definition of apparent brightness, which units are appropriate for its measurement? |
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Definition
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Term
| Suppose two stars are identical except that one is twice as far away from us as the other. Which statement is true? |
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Definition
| Both stars have the same luminosity, but the apparent brightness of the closer star is four times as great as that of the more distant star. |
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Term
| Suppose that a star has a parallax angle of 1/20 arcsecond. If so, it is |
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Definition
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Term
| Which of the following statements about spectral types of stars is NOT generally true? |
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Definition
| The spectral type of a star can be used to determine its distance |
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Term
| Sirius is a spectral type A star whereas Rigel is a spectral type B star. What can we conclude? |
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Definition
| Rigel has a higher surface temperature than Sirius. |
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Term
| Astronomers generally can measure a star's mass if only it is a member of a binary star system. What characteristics of the stars must we know to measure the masses of the stars in a binary system? |
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Definition
| Their orbital period and average orbital distance |
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Term
| 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 dimmer for about 2 hours. The most likely explanation is that: |
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Definition
| The star is a member of an eclipsing binary star system |
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Term
| You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R diagram. You will need to determine all of the following, except: |
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Definition
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Term
| The approximate main-sequence lifetime of a star of spectral type O is |
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Definition
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Term
| For a Cepheid variable star, the longer the time between peaks of brightness, the ______. |
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Definition
| greater the luminosity of the star. |
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Term
| How did astronomers discover the relationship between spectral type and mass for main sequence stars? |
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Definition
| Astronomers discovered the relationship by measuring the masses of main sequence stars in binary systems, and assume that the same relationship holds for single stars as well |
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Term
| The choices below each describe the appearance of an H--R diagram for a different star cluster. Which cluster is the youngest? |
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Definition
| The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants |
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Term
| 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? |
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Definition
| The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs |
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Term
| Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true? |
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Definition
| A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage |
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Term
| Which two processes can generate energy to help a star maintain its internal thermal pressure? |
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Definition
| nuclear fusion and gravitational contraction |
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Term
| Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, etc.) in a high-mass star is NOT true? |
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Definition
| Each successive stage lasts for approximately the same amount of time |
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Term
| 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? |
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Definition
| 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 |
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Term
| What process distributes most of the carbon in the universe? |
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Definition
| Winds from low-mass red giant stars. |
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Term
| Which event marks the beginning of a supernova? |
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Definition
| The sudden collapse of an iron core into a compact ball of neutrons |
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Term
| 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? |
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Definition
| At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions |
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Term
| Our Sun is considered to be a ______. |
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Definition
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Term
| 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? |
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Definition
| A main-sequence star is hotter and dimmer than it was as a protostar. |
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Term
| Close binary star systems are thought to form when _____. |
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Definition
| a protostar is spinning so fast that it splits in two |
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Term
| Which of the following statements about black holes is NOT true? |
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Definition
| 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 |
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Term
| According to present understanding, a nova is caused by ______. |
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Definition
| the fusion of hydrogen on the surface of a white dwarf. |
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Term
| Which statement concerning black holes masses and Schwarzschild radii is NOT true? |
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Definition
| The maximum mass for a black hole corresponds to one with a Schwarzschild radius of 100 km |
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Term
| The white dwarf that remains when our Sun dies will be mostly made of ______. |
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Definition
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Term
| Which of the following statements about gamma ray bursts is NOT true? |
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Definition
| The events responsible for gamma-ray bursts apparently produce ONLY gamma rays, and no other light that we can hope to detect |
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Term
| Which statement about pulsars is NOT thought to be true? |
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Definition
| Pulsars can form only in close binary systems |
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Term
| Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? |
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Definition
| Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted |
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Term
| What prevents a white dwarf from having a mass greater than the white dwarf limit (or Chandrasekhar limit)? |
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Definition
| Electron degeneracy pressure depends on the speeds of electrons, and as a white dwarf's mass approaches the white dwarf limit, its electron speeds are already approaching the speed of light |
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Term
| The Voyager spacecraft has 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? |
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Definition
| Pulsars are easy to identify by their almost perfectly steady periods of pulsation |
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Term
| If a neutron star or black hole is accreting material from its companion in a close binary, which of the following observatories would offer us the best chance for discovering this fact? |
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Definition
| Chandra X-Ray Observatory |
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Term
| The more massive a white dwarf, the ______. |
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Definition
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Term
| Will our Sun ever undergo a white dwarf supernova explosion? Why or why not? |
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Definition
| No, because it is not orbited by another star. |
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Term
| 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? |
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Definition
| The entire mass of the Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. |
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