Test Answers on Astronomy Exam 3 - Flashcards

Q: What is the most important defining property of the Trojan asteroids?

They orbit the Sun in the same path as Jupiter and 60Â° ahead of and behind it.

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What is the most important defining property of the Trojan asteroids?

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They orbit the Sun in the same path as Jupiter and 60° ahead of and behind it.

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What is the source of the material of a meteor shower?

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Comets

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What are the objects known as Gaspra and Ida?

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Moderately large S-type asteroids in the main asteroid belt

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The tail of a comet can consist of ________.

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dust and gas

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Which of the following characterizes the Kuiper belt?

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It is a disk-like region between the outer planets and the Oort cloud.

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Which of the following is NOT one of the criteria necessary to classify an object as a major planet? A. It must have at least one moon orbiting around it. B. It has cleared its neighborhood around its orbit of other bodies. C. It must orbit the Sun. D. It must have enough self-gravity to be approximately spherical.

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A. It must have at least one moon orbiting around it.

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The ingredients of a typical comet's nucleus are most likely ________.

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dust and rocky particles trapped in methane, ammonia, and water ice

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Why do researchers believe that asteroids in the asteroid belt are primal rocks that did not merge into a planet?

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A. The differences in chemical compositions of the asteroids are too large for them to have originated in a single body. B. Jupiter's gravity could have prevented these objects merging into a single body. C. The total mass of the asteroids in the asteroid belt is much smaller than that of any terrestrial planet in our solar system. D. All of the above.

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The tail of a comet always points:

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away from the Sun and becomes longest and brightest at perihelion.

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How was Pluto discovered?

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It was simple luck and hard work.

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From its orbit, we now recognize Pluto as one of the largest members of the:

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Kuiper Belt.

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Meteor shower debris is believed to come from:

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the disintegration of a short period comet over many returns to the Sun.

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Planetesimals were created through what process?

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accretion

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Models that explain the formation of the solar system through a series of gradual steps are considered evolutionary theories. What are models that explain the formation of certain objects in the solar system through other means considered?

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catastrophic theories

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Which of the following methods have astronomers used to detect extrasolar planets?

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Extrasolar planets have been detected using all of the methods listed here.

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Which of the following extrasolar planets would be easy to detect?

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a Jupiter-sized planet orbiting close to a star

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What is a "hot Jupiter?"

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A planet with Jupiter's mass orbiting very close to its star.

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What is a brown dwarf?

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An object with more mass than Jupiter, but not enough mass to become a star.

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What is a habitable zone?

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the region around a star where liquid water can exist on or near a planetary surface

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The temperature of the layer of gas that produces the visible light of the Sun is:

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5,800 K.

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The luminosity of the Sun is a measure of:

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the total energy emitted by the Sun in all directions.

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Hydrostatic equilibrium in our Sun is the balance between:

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gravitation and pressure.

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What two energy transport mechanisms, in order from outside the core to the surface, are found in the Sun?

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radiative diffusion, convection

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From where does most of the solar wind flow?

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coronal holes

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The percentage (by mass) of the Sun that is Hydrogen is about:

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71%.

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A loop of gas following the magnetic field lines between sunspots' poles is:

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a prominence.

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What is the term for loops or sheets of glowing gas ejected from active regions on the solar surface?

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prominences

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What is the common cause of sunspots, flares, and prominences?

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magnetic fields

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What is the primary source of energy for the Sun?

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hydrogen fusion

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The Sun has sufficient hydrogen to continue fusing into helium for how much longer?

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5 billion years

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What is the "solar neutrino problem"?

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Too few neutrinos are detected on Earth compared to the number the solar model predicts.

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What is the surface temperature of the Sun?

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5800 K

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Why does the surface of the Sun appear to have a sharp edge?

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The photosphere is relatively thin compared to the other atmospheric regions.

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Granulation is evidence of what phenomenon?

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convection in the solar interior

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All the photons produced in the Sun's core have been absorbed by the outer edge of what region of the Sun?

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radiation zone

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The solar spectrum is a good example of what kind of spectrum?

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absorption

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From which region of the Sun does the solar wind originate?

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corona

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During periods of low solar activity just after solar minimum, what is true of the location and distribution of sunspots?

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They tend to cluster at high solar latitudes.

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Why do sunspots appear dark?

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They have lower temperatures.

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Which of the following statements about solar sunspots is NOT true? A. They reach maximum numbers at roughly 11-year intervals. B. They are distributed approximately uniformly over the Sun's surface both in position and in time. C. They typically measure about 10,000 km across (approximately the size of Earth!). D. They cluster at high latitudes when solar activity is at a minimum. E. They appear in larger numbers at about the time of the solar maximum.

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B. They are distributed approximately uniformly over the Sun's surface both in position and in time.

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What information do we know about the known exoplanets?

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estimates of orbits and masses

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The condensation theory is an example of:

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an evolutionary theory.

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The Doppler radial velocity technique works best for:

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planets whose orbits are along our line of sight.

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When we are lucky enough to see an extra-solar planet transit its star,

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we can find the planet's size, mass, and density by the drop in light.

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Extrasolar planetary systems are similar to our solar system in all of the following ways, EXCEPT: A. that planets orbit in the same direction that their parent star rotates. B. that the systems contain interplanetary debris, such as comets or asteroids. C. for the presence of hot Jupiters in some systems. D. that planetary orbits are relatively coplanar. E. None of these are dissimilar to our solar system.

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C. for the presence of hot Jupiters in some systems.

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Loops of glowing hydrogen seen hanging over the solar limb during totality are:

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promiences.

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In the proton-proton cycle, the helium atom and neutrino have less mass than the original hydrogen. What happens to the "lost" mass?

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It is converted to energy.

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Suppose two stars with the same luminosity are at different distances from Earth. Which has the greater apparent brightness?

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the closer star

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What important property of a star do we learn from its spectral class?

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temperature

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Which of the following methods is useful for determining a star's approximate surface temperature?

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measuring its apparent brightness through two or more color filters and comparing these values

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Why are we unable to measure parallax shifts for most of the stars in the Galaxy?

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They are too far away.

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Our Sun is classified as a G2 star. Vega, which is 26.4 light-years away, is an A0 star, and Barnard's Star is type M5. How do these stars compare in terms of temperature?

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Vega is hotter than the Sun, which in turn is hotter than Barnard's Star.

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Which type of star motion can be measured using the Doppler Effect?

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Radial motion

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Absolute magnitude directly allows us to compute what intrinsic property of a star?

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Luminosity

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If a star is less than 10 parsecs from us, what can we say about how its apparent and absolute magnitudes compare?

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Absolute magnitude will be the larger number.

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If you want to find a radius value for most stars, what must you first measure about the star?

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Luminosity and temperature

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An H-R diagram is a plot of which two stellar properties?

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luminosity and temperature

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Which stars are most common in the Galaxy?

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red dwarfs

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Why are the most common stars among the most difficult to observe?

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They have low luminosities.

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Three M-class stars are identified as main-sequence, giant, and supergiant, respectively. In which physical property do they differ?

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luminosity

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In spectroscopic parallax, a star's spectral type and what other property are used to determine an approximate distance?

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apparent brightness

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What property of stars can be measured only by using binary-star systems?

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mass

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A high-mass star has more "fuel" than a low-mass star. Which lives longer? Why?

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The low-mass star lives longer because, even though it has less "fuel," it consumes fuel at a much slower rate than the high-mass star.

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Low-mass stars have much longer lifetimes than high-mass stars. Which stellar property is a direct cause of this difference?

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luminosity

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If a star appears to move back and forth relative to other stars over a six-month period, this motion is due to the star's:

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parallax shift.

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The absolute magnitude of a star is its brightness as seen from a distance of:

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ten parsecs.

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Star A and star B both have an apparent magnitude of 4.0, but star A has an absolute magnitude of 1.0 and star B has an absolute magnitude of 7.0. Which statement below is correct?

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Star A and star B appear to have the same brightness, but actually star A is brighter than star B.

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What physical property of a star does the spectral type measure?

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temperature

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Star A is a main sequence star of spectral type G5 and star B is a red giant of spectral type K2. Which statement below is correct?

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Star A is hotter than star B.

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The Hertzsprung-Russell Diagram plots ________ against the spectral type or temperature.

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luminosity or absolute magnitude

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On the H-R diagram, red supergiants like Betelguese lie:

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at the top right.

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Having nothing to do with trigonometry, ________ parallaxes use the width of absorption lines to estimate the star's luminosity and size and distance.

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spectroscopic

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In a spectroscopic binary system, the star showing the larger blue shift is:

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less massive and approaching us at this moment.

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What is the typical main sequence lifetime of a G-type star?

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10 billion years

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Despite its low density, dust can completely block starlight because of which of the following?

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the large distances involved

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What are the main constituents of interstellar gas?

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hydrogen and helium

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Which constituent of interstellar matter obscures visible light?

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dust

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What type of nebula contains stars of spectral types O and B?

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an emission nebula

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Why is 21-cm radiation important?

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It enables us to study dark clouds in the interstellar medium.

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Why are molecules like CO, HCN, NH3, H2O, and H2CO important for studying the interstellar medium?

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They allow us to locate and trace out the structure of cool, dark clouds.

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Which of the following best describes the shape of interstellar dust particles?

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rodlike

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If you took a large sample of interstellar material and compressed it to the density and temperature typical of Earth's atmosphere, how would it probably appear?

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much more opaque than Earth's air

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If an interstellar cloud lies between Earth and a hot star, we can detect its presence in the stellar spectrum of the star. Which of the following properties of the cloud CANNOT be determined from the stellar spectrum? A. velocity B. density C. elemental abundance D. temperature E. All of the above properties can be determined.

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E. All of the above properties can be determined.

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What observation has enabled astronomers to determine the approximate shape of interstellar dust particles?

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how they polarize light

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Why are reflection nebulae blue and emission nebulae red?

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Reflection nebulae scatter blue light, and emission nebulae emit red light.

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The average temperature of the typical dark dust cloud is about:

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100 K.

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Which of the following statements best describes globular clusters?

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They contain from hundreds of thousands to millions of stars and have a typical size of about 50 parsecs.

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A small group of atoms does not collapse into a clump because ________ quickly disperses them.

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heat

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What temperature is required to initiate nuclear fusion in a stellar core?

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10,000,000 K

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For gravity to contract a spinning interstellar cloud, what must be present in sufficient amount?

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mass

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What event must occur in order for a protostar to become a full-fledged star?

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the onset of hydrogen fusion

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What are brown dwarfs?

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low-mass objects that never become stars

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How do astronomers know that stars (and their planetary systems) form from concentrations of interstellar material? A. Emission nebulae have been shown to contain young stars. B. Detailed high-resolution photographs have revealed the presence of protostellar and protoplanetary disks in star-forming regions of nebulae. C. It is completely a matter of conjecture because none of the stages of star formation can be observed experimentally. D. Groups of stars nearest to molecular clouds tend to be younger than those farther away from such clouds. E. All the pieces of evidence listed here contribute to this conclusion.

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E. All the pieces of evidence listed here contribute to this conclusion.

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How do high-mass stars aid in the star formation process?

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They create shock waves that compress the surrounding gas and trigger collapse.

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Why do star clusters provide excellent tests for theories of stellar evolution?

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The stars in any particular cluster formed at roughly the same time from the same primary material and under the same environmental conditions.

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What is the force that keeps a main sequence star from blowing apart?

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gravitation

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In the collapsing cloud fragment stage (stage 2) of star formation, the size of the cloud fragment is about:

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100 times the size of the solar system.

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From stage 4 to stage 7 of star formation, the object plotted on the H-R diagram moves so that:

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its luminosity decreases, while its temperature increases.

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Higher mass protostars enter the main sequence:

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faster and at a higher luminosity and temperature.

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Besides mass the other factor that influences where a star appears on the main sequence is:

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chemical composition of the cloud.

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Protostars can be observed in:

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the Orion Nebula.

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Why is the depletion of hydrogen in the core of a star such an important event?

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The star will begin to change its structure drastically.

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Hydrogen-shell burning proceeds increasingly faster due to which of the following?

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heat released from the core's contraction

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As a low-mass main-sequence star runs out of hydrogen fuel in its core, it actually becomes brighter. How is this possible?

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The outer layers expand due to the higher rate of fusion in a shell around the dead core.

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In a white dwarf, what is the source of pressure that ultimately halts its contraction?

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electrons packed so closely that they become incompressible

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What is the primary composition of a white dwarf?

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carbon

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In its last stage of evolution, what will the Sun become?

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white dwarf

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What property of a star cluster helps determine its age?

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main-sequence turnoff

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What is a contact binary?

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two nuclear-burning stellar cores surrounded by a single continuous common envelope

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A star (no matter what its mass) spends most of its life:

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as a main sequence star.

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Why are star clusters almost ideal "laboratories" for stellar studies?

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Stars in clusters have the same age, similar composition, and are at the same distance away.

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The most important fact about a cluster of stars that makes them useful for studying star formation is that

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all the stars formed at about the same time.

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When a star depletes its core supply of hydrogen, ________ dominates in the core and ________ dominates in the envelope.

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gravity; pressure

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What is the region of the Hertzsprung-Russell diagram known as the horizontal branch?

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It is a region of the H-R diagram where stars remain for a time as they undergo helium core fusion.

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What is a planetary nebula?

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an expanding shell of gas around a white dwarf star

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What is the size of the core of a typical white dwarf star?

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about the size of Earth

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As a 4-10 solar mass star leaves the main sequence on its way to becoming a red supergiant, its luminosity:

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remains roughly constant.

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What is the age range among the globular clusters associated with our Galaxy?

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The globular clusters range from 10 to 12 billion years old.

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Why do the cores of massive stars evolve into iron rather than heavier elements?

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Fusion of heavier elements disrupts the stability of the core by requiring more energy than it generates.

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Which of the following is the best description of the interior structure of a highly evolved high-mass star late in its lifetime but before the collapse of its iron core?

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An onion-like set of layers forms, with the heaviest elements in the innermost shells surrounded by progressively lighter ones.

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Will the Sun ever explode as a Type I supernova?

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No. It lacks a binary companion.

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Which stars eventually undergo supernova explosions?

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the most massive stars

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Why does the spectrum of a carbon-detonation supernova (Type I) show little or no hydrogen?

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This supernova is the detonation of a carbon white dwarf that contains virtually no hydrogen.

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Figure 21.13 in your book shows that elements with an even number of protons are more abundant than elements with an odd number of protons. Why is this so?

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Many elements are built by capturing one or more helium nuclei, each of which contains two (an even number) protons.

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Where are lighter elements fused into elements more massive than iron?

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a supernova

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What mechanism produces a nova?

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If a white-dwarf star is close enough to a binary-companion star to steal material from it, the material eventually heats up to a temperature high enough to cause fusion on its surface.

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The total energy emitted by the brightest nova explosions is about:

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a million suns

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Most of the energy of the supernova is carried outward via a flood of:

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neutrinos

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Which of these is the likely progenitor of a type I supernova? A. an evolved red giant which is just starting to make silicon in its core B. an evolved blue supergiant that is about to experience the helium flash C. a helium-neon white dwarf D. a mass-transfer binary, with the white dwarf already at 1.3 solar masses E. a contact binary, with the neutron star at 2.3 solar masses

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D. mass-transfer binary, with the white dwarf already at 1.3 solar masses

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Nearly all the elements found in nature were formed inside stars, EXCEPT for:

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hydrogen and helium

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Type II supernovae and star forming regions are related to one another because: A. they both involve high mass ionizing stars. B. they both contain ionized hydrogen. C. the shock waves of a supernova can trigger star formation. D. as a result of both processes, lighter elements are transformed into heavier elements. E. All of the above.

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E. All of the above.

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What have astronomers detected in the center of the Crab Nebula?

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a neutron star

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What process is responsible for producing the rapid spin rate of millisecond pulsars?

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Gas spiraling in from a nearby companion transfers angular momentum to the pulsar, increasing the rate of its rotation.

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What do the observed locations of gamma-ray bursts tell us about them?

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They must be extra-galactic because they occur everywhere in the sky.

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What keeps light (and all other forms of radiation) from escaping a black hole?

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gravity

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At what stage of its life will our Sun become a black hole?

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The Sun will never become a black hole

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What effect predicted by Einstein's theory of general relativity is confirmed during a solar eclipse?

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deflection of light from distant stars by the gravitational field of the Sun

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Why is light increasingly redshifted near a black hole?

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It must expend energy to escape the gravitational pull of the black hole.

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Which of the following is NOT an observational feature associated with the binary-star system Cygnus X-1, which is suspected of containing a black hole?

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A small, dark region in the space near the visible companion indicates that light cannot escape from that region, which is the characteristic feature of a black hole.

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Which of the following is NOT a characteristic feature of a neutron star?

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A radius about the size of the Earth's

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In a neutron star, the core is:

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made of compressed neutrons in contact with each other.

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Which of the following is NOT a reason that observable pulsars are found at the centers of some, but not all, supernova remnants?

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Type II core-collapse supernovae do not leave behind rotating neutron stars.

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What compelling evidence links pulsars to neutron stars?

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Only a small, very dense source could rotate that rapidly without flying apart.

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A proposed explanation for gamma-ray bursters is: A. hypernova-making black holes and bi-polar jets. B. coalescence of a neutron star binary. C. collisions between two white dwarfs. D. Both A and B are possible. E. All three are possible.

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D. Both A and B are possible.

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What defines the event horizon of a black hole?

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the radius at which the escape speed equals the speed of light

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Which of the following can actually escape from inside a black hole's event horizon? A. neutrinos B. very high energy gamma-rays C. gravitons D. electrons E. None of the above

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E. None of the above

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A method for identifying a black hole is to:

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look for their effects on nearby companions.

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In which of the basic regions of the Galaxy is the Sun located?

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galactic disk

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What is the approximate distance of our Sun from the center of the Galaxy?

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8 kpc

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Which statement best describes the distribution of halo stars and globular clusters and the location of our Sun, relative to the galactic disk of the Milky Way Galaxy?

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The halo stars and globular clusters are distributed in a roughly spherical region surrounding and centered on the disk; the Sun is located roughly halfway out from the center in the plane of the disk.

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What model did the 18th-century astronomer William Herschel develop regarding the location of the solar system within our Galaxy?

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He thought the solar system was near the center of a somewhat flattened, roughly disk-shaped collection of stars lying in the plane of the Milky Way.

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What types of stars tend to be found along spiral arms in the Milky Way and other similar galaxies?

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A larger number of young, bright stars are found in the spiral arms than in other regions of these galaxies.

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Which is the oldest component of the Milky Way Galaxy?

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the halo

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What type of observation is used for mapping large-scale galactic structure?

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21-cm radio emission of atomic hydrogen

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A rotation curve, which plots the rotation speeds of objects as a function of their distance from the center of the Milky Way Galaxy, can be used to determine which property of the Galaxy?

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mass

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There is a small source of intense radiation at the center of our Galaxy that may have a mass of about how many solar masses?

answer

4,000,000 Suns

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In structure, our Milky Way is most similar to: A. the Orion nebula. B. M-31, the Andromeda Galaxy. C. the Large Magellanic Cloud. D. an upscale version of a globular cluster. E. None of these.

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B. M-31, the Andromeda Galaxy.

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How do astronomers know the distances to Cepheid variables?

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By measuring the period of the variable star, we can determine its luminosity. Then, by measuring its apparent brightness, we can use the inverse-square law of light to get its distance.

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A star in the instability strip of the H-R diagram would:

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vary in both temperature and radius.

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From Earth, the view of the Milky Way is a thin band of stars across the night sky. The part of the Milky Way galaxy that is described here is the:

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disk.

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Which sequence of formation by age is correct, oldest to youngest?

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globular clusters, emission nebulae, open clusters

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The leading explanation for the existence of spiral arms are:

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passages of spiral density waves through the interstellar medium.

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Most of the mass of the Milky Way seems to exist in the form of:

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dark matter out in the Halo.

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What observations suggest the mass of the Galaxy goes much farther out than its visible disc?

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the rotation curve of the outermost portions of the disc

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A high-velocity ring or disk of gas just a few parsecs across at the center of the Galaxy suggests that the exact center is occupied by which of the following?

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supermassive black hole

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Which of the following types of galaxies has experienced no significant star formation during the last 10 billion years?

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elliptical

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The Tully-Fisher relation uses the close correlation between the rotational speed of a spiral galaxy and its luminosity as a distance indicator. Why does this correlation exist?

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The greater the mass of a galaxy, the faster it spins, and the more mass there is to give off light.

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Why do errors and uncertainties in distance measurements get bigger the farther out we measure?

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The techniques used to measure far distances are calibrated by using more local measurements; therefore, any errors accumulate.

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According to Hubble's law, as the distance to galaxies ________, the ________ increases.

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increases; apparent recessional velocity

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From Hubble's law, what single observation of a galaxy is needed to determine its distance from us?

answer

recessional velocity

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The fact that the energy output of active galactic nuclei can be highly variable indicates that the central object emitting the energy is which of the following?

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much less than a parsec across

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What is observed that connects radio emissions in the galactic nucleus with the emissions in the halo or radio lobes?

answer

There is a jet of matter coming out of the nucleus, which often points toward the lobes.

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How does the energy output from active galactic nuclei differ from the energy output from normal galaxies?

answer

The emission of active galactic nuclei is nonstellar, whereas the emission of a normal galaxy is stellar.

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Which of the following is NOT a characteristic of an active galaxy? A. a regular, rapid pattern of radio frequency and optical emission peaks ranging from milliseconds to seconds in repetition rate B. broad emission lines indicative of rapid internal rotation C. energy emission that is highly variable on timescales of a few years D. jets along their central rotational axes E. luminosities higher than can be explained by the number of stars they contain

answer

A. a regular, rapid pattern of radio frequency and optical emission peaks ranging from milliseconds to seconds in repetition rate

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