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AstronomyFINAL
| Question | Answer |
|---|---|
| Which of the following best describes why we have seasons on Earth? | The tilt of Earth's axis causes different portions of the Earth to receive more or less direct sunlight at different times of year. |
| About how old is our Solar System? | 5 billion years old |
| What effect or effects would be most significant if the Moon's orbital plane were exactly the same as the ecliptic plane? | Solar eclipses would be much more frequent. |
| Which of the following correctly compares the Sun's energy generation process to the energy generation process in human-built nuclear power plants? | The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei. |
| Based on observations of the cosmic microwave background, the overall composition of the universe is approximately ________. | 4% ordinary (baryonic) matter, 23% non-ordinary (nonbaryonic) dark matter, 73% dark energy |
| Is space expanding within clusters of galaxies? | No, because their gravity is strong enough to hold them together even while the universe as a whole expands. |
| Which of the following is not evidence for dark matter? | the expansion of the universe |
| From evidence of white dwarf supernovae it appears that the current state of the universe is | accelerating because of dark matter particles |
| Which statement about motion in the universe is not true? | The mysterious dark matter is the fastest-moving material in the universe. |
| In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked by the Cosmic Microwave Background Radiation for times prior to about 380,000 years after the Big Bang. Why? | Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely. |
| The big bang is a theory about a location in space where the entire universe was contained at one point in the past into a small spot before expanding rapidly. | False |
| 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 = 20 km/s/Mly. How fast would a galaxy 1000 Mly distant be receding from us? | 20,000 km/s |
| Compared to spiral galaxies, elliptical galaxies are | redder and rounder. |
| 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. |
| This figure shows Hubble's law. If a galaxy is observed to be moving away from us at 30,000 km/s, how far away is it? | about 1400 million light-years |
| How did Edwin Hubble measure the distance to the Andromeda Galaxy? | He applied the period-luminosity relation to Cepheid variables in Andromeda. |
| 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. |
| In this picture, we are seeing light from the circled elliptical galaxy (HUDF-JD2) from when the universe was only about 800 million years old. The spiral galaxy below it is much closer. Why does HUDF-JD2 appear a deep red, compared to the whitish color o | At such a large distance, all the light emitted by it is very redshifted. Even at this young age, the galaxy contains few high mass blue stars. |
| What makes white-dwarf supernovae very good standard candles for distance measurements? | They are very bright, so they can be used to determine the distances to galaxies billions of light-years away. They should all have approximately the same luminosity. |
| Which types of galaxies have a clearly defined disk component? | spirals and lenticulars |
| This figure shows the Cepheid period-luminosity relation. What is the approximate luminosity of a Cepheid star that varies in brightness on a 10 day cycle? | about 10,000 times the luminosity of the sun |
| In the 1960s, Maarten Schmidt determined that quasars were very distant objects by | determining their redshifts. |
| How do observations of galaxies at different distances help us learn about galaxy evolution? | Observations of different distances show galaxies of different ages and therefore different stages of evolution. |
| As a solar mass protostar moves on to the main sequence, | its surface temperature increases and its luminosity decreases. |
| What percentage of a star's total lifetime is spent on the main sequence? | 90% |
| Compared to the star it evolved from, a white dwarf is | hotter and dimmer. |
| What is a planetary nebula? | the expanding shell of gas that is no longer gravitationally bound to the remnant of a low-mass star |
| Stars with high masses live longer than stars with lower masses. | False |
| Which two processes can generate energy to help a star maintain its internal thermal pressure? | nuclear fusion and gravitational contraction |
| What is the fate of an isolated brown dwarf? | It will remain a brown dwarf forever. |
| Which event marks the beginning of a supernova? | the sudden collapse of an iron core into a compact ball of neutrons |
| Which of the following is not true about differences between novae and supernovae? | Supernovae eject gas into space, but novae do not. |
| Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova? | The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not. |
| Pulsars are thought to be ________. | rapidly rotating neutron stars |
| What causes the radio pulses of a pulsar? | As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse. |
| Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its mass reaches the 1.4 solar mass limit? | The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion. |
| In which wavelength region(s) would we need to carry out observations in order to study the accretion disk around a white dwarf in a binary system? | B and C |
| What is the ultimate fate of an isolated pulsar? | It will spin ever slower, the magnetic field will weaken, and it will become invisible. |
| After a massive-star supernova, what is left behind? | either a neutron star or a black hole |
| Star A has an apparent magnitude of 3, and Star B has an apparent magnitude of 5. Which star is brighter in our sky? | Star A |
| On the main sequence, stars obtain their energy | by converting hydrogen to helium. |
| Which of the following is the most numerous type of main-sequence star? | O and B stars |
| Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass? | The star is a member of a binary star system. |
| What can we infer, at least roughly, from a star's luminosity class? | its size (radius) |
| The apparent brightness of an object is calculated as: | apparent brightness=luminosity/4pie*distance^2 |
| If one knew the luminosity and apparent brightness of a star that was too distant for a parallax measurement, what would be the best approach to determining its distance? | Solve the equation for distance, then insert the values for luminosity and apparent brightness into the new equation. |
| Which of the following terms is given to a pair of stars that appear to change position in the sky, indicating that they are orbiting one another? | visual binary |
| A star is observed with a surface temperature of 3,000 K and a luminosity of 10−2 solar. What is the approximate mass of this star? | 0.2 Msun |
| Which of the following comparisons between low-mass stars and high-mass main-sequence stars is true? | Low-mass stars are cooler and less luminous than high-mass stars. |
| Which of the following statements about apparent and absolute magnitudes is true? | The absolute magnitude of a star is another measure of its luminosity. The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. |
| Which of the following statements about apparent and absolute magnitudes is true? | A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2. A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. |
| What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse? | outward pressure due to super-heated gas |
| Sunspots are cooler than the surrounding region of the Sun's surface. | True |
| Approximately how many neutrinos pass through your body each second? | about a thousand trillion |
| How do we test our computer models for the interior of the Sun? | comparing model predictions to how the Sun actually vibrates |
| Why isn't the Sun shrinking or expanding? | because gas pressure balances gravity in the Sun |
| What is the only force that can overcome the repulsion between two positively charged nuclei to bind them into an atomic nucleus? | the strong force |
| Which of the following quantities is equal to the energy per second generated by the Sun's nuclear reactions? | the luminosity of the Sun's photosphere |
| The chromosphere is the layer of the Sun that we see as its visible surface. | False |
| If the sun's surface cooled, how would its appearance change? | It would appear more red. |
| Suppose you try to bring two protons close together. Because of the electromagnetic force, the two protons will | repel one another. |
| How do we know how old the Sun is? | from ages of solar system meteorites, based on radioactive elements |
| The proton-proton chain converts four hydrogen nuclei into one helium nucleus plus energy. | True |
Created by:
willi5