Term
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Definition
1. ejects matter into space at high velocity
2. can shine as bright as an entire galaxy for a few weeks
3. is the result of the core of a star collapsing violently
4. can leave behind a neutron star or a black hole
5. can create atomic nuclei with more protons than iron |
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Term
| Q16 A red giant is a star that... |
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Definition
1. is cooler and more rarefied on the outside, but hotter and denser in its core than a main-sequence star with the same surface temperature
2. will shed its outer layer into space
3. seeds regions around the star with heavy elements |
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Term
| Q17 An extrasolar planet or exoplanet is a... |
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Definition
| planet outside of the solar system |
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Term
| Q17 The radial velocity technique is based on... |
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Definition
| measuring the velocity of a star as it moves towards or away from the observer |
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Term
| Q18 The hypothesis that giant planets around other stars are also composed primarily of gas was confirmed by... |
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Definition
| observations of one planet passing in front of its host star that allowed astronomers to measure the planet's size and density |
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Term
| Q18 The discovery of giant planets on eccentric orbits led astronomers to hypothesize that... |
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Definition
1. giant planets formed in nearly circular orbits, but close encounters between planets perturbed the orbits into an elliptical shape
2. some of these objects might be brown dwarfs that are believed to form in eccentric orbits, more similar to how stars form than how planets form |
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Term
| HW5 A supernova explosion can create... |
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Definition
1. a temporary flash of very bright light
2. most of the very heavy elements |
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Term
| HW5 Many astronomers believe that the star Beta Pictoris has at least one planet because... |
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Definition
1. The midplane of the disk is warped
2. At some wavelengths, the disk has different extends in the southeast and northwest directions
3. At some wavelengths, the disk appears to have clumps of dust |
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Term
| HW5 The width of the habitable zone around a ~64 solar luminosity star is roughly... |
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Definition
6.9 AU
The width of the Sun's habitable zone is ~0.86 AU. The square root of 64 is 8. 0.86 x 8 = 6.88 AU. |
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Term
| HW5 Most stars within 100 parsecs of the Sun... |
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Definition
1. have a main-sequence lifetime greater than that of the sun
2. have a mass less than that of the Sun
3. have a habitable zone narrower than that of the Sun
4. have a habitable zone with a radial separation from its host star that is expanding less rapidly than that of the Sun |
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Term
| HW5 The radial velocity technique for detecting extrasolar planets is... |
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Definition
1. more easily able to detect high mass planets than low mass planets
2. more easily able to detect planets with small orbital periods than large orbital periods
3. able to detect planets with small radii and planets with large radii equally well
4. based on precise measurements of the wavelength of absorption lines in the spectra of the planet's host star |
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Term
| HW5 In order for a planet to be confidently detected by the radial velocity technique, which of the following observations need to be made? |
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Definition
1. Observations of the brightness of the star that demonstrate the star is not rotating with a period very similar to the period seen in radial velocity observations
2. Radial velocity observations spanning multiple orbital periods that show periodic variations
3. Many radial velocity observations that clearly deviate from the expectations if the star had a constant velocity towards/away from the solar system
4. Observations that demonstrate that the shape of the star's absorption lines do not change in sync with the inferred radial velocity variations |
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Term
| HW5 The majority of extrasolar planetary systems discovered by the radial velocity technique differ from our solar system in that they contain... |
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Definition
1. at least one giant planet closer to their star than any giant planets in our solar system
2. at least one giant planet on an orbit more eccentric than the orbits of the giant planets in our solar system |
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Term
| HW5 How have planet formation theories been modified in light of the discovery of extrasolar planets with orbital properties different from the planets in our solar system? |
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Definition
1. Giant planets formed farther from their star and later migrated inwards to explain how ice formed
2. Since multiple planet systems have been found with two planets in mean-motion resonances, scientists hypothesize that the two planets formed farther apart and then migrated at different rates before becoming captured into the resonance
3. Giant planets formed on circular orbits and later had their orbits altered more eccentrically by close encounters with other planets that have since been ejected |
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Term
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Definition
1. is a system of telescopes that can provide a spatial resolution much greater than that of any one of the individual telescope
2. must combine the light from multiple sources very precisely in order to function properly |
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Term
| Q20 In the coming decade or two, astronomers hope to directly detect optical light from an extrasolar planet, since this would allow them to... |
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Definition
1. study the temporal changes in the brightness of the planet as the cloud coverage changes with the seasons
2. take spectra of the planet and search for absorption lines that indicate the composition of its surface and/or atmosphere
3. study the temporal changes in the brightness of the planet as different regions of the surface rotate into view |
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Term
| Q21 The "red edge" refers to... |
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Definition
| A sharp increase in the amount of light reflected by terrestrial plants at near infrared wavelengths |
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Term
| Q21 Detecting a red edge feature on the Earth would be difficult for distant observers because... |
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Definition
1. most of Earth's surface is covered by oceans and deserts that do not produce a red edge feature
2. much of Earth's surface is covered by clouds that block any red edge feature from the surface below
3. it is only a few to 10 percent effective |
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Term
| Q22 The "Drake Equation" refers to... |
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Definition
| An equation to estimate the number of communicating civilizations in our galaxy |
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Term
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Definition
| The spread in the frequency range used for transmitting or receiving an electromagnetic signal |
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Term
| Q23 Searching for signals from another civilization at radio wavelengths makes more sense than at optical wavelengths, because... |
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Definition
1. radio waves are less prone to absorption or scattering by interstellar gas and dust
2. less energy is required per photon at radio wavelengths
3. the planet's host star will emit less radiation at radio wavelengths than optical wavelengths, resulting in less intereference |
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Term
| Q24 Why have we not yet been contacted by aliens? |
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Definition
1. There are not many technologically advanced civilizations in the galaxy.
2. Aliens have little interest in contacting us, given that it is unlikely to be useful
3. We do not yet possess the necessary technology to receive their signals
4. The lifetime of technologically advanced civilizations is so short that they don't have time to contact us |
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Term
| HW6 The amount of the decrease in observed starlight when a planet passes in front of a star is proportional to... |
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Definition
| The square of the ratio of the radius of the planet to the radius of the star |
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Term
| HW6 The gravitational pull of a planet orbiting a star results in the star wobbling which can be detected by... |
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Definition
1. repeatedly observing the angular separation between the target star and other background stars to measure slight changes in the position of the star
2. repeatedly observing spectra of the star to measure the changes in the radial velocity of the star towards or away from our solar system |
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Term
| HW6 Directly imaging a planet around another star is very difficult because... |
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Definition
1. The planet is small, far away, and faint.
2. For a single large ground-based telescope, rapid fluctuations Earth's atmosphere would smear out the light of the star and planet so that they would blend together.
3. It is hard to design a telescope and detector that can see a faint planet very close to a bright star.
4. For a single large space-based telescope, the resolution is limited by the size of the primary mirror. Resolving the planet would require a large and therefore expensive telescope. |
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Term
| HW6 Over the course of one year, an outside observer looking at the solar system with an observatory similar to TPF-C would be able see that the apparent brightness of the Earth at optical wavelengths varies as a function of time due to... |
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Definition
1. different surface features AND cloud patterns rotating into and out of view, as the Earth spins about its rotation axis
2. the changing seasons that cause changing weather patterns, including the amount of cloud coverage over different parts of the Earth
3. the changing angle between the observer, sun, and Earth, as the Earth orbits the sun |
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Term
| HW6 What observations would provide evidence supporting the claim that a distant planet harbors some form of life? |
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Definition
1. A spectrum of the planet shows absorption by both molecular oxygen and methane; ozone and methane; and molecular oxygen and nitric oxide.
2. The detection of a sharp change in the planet's brightness as a function wavelength that does not match the spectrum of any known substance. |
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Term
| HW6 Using an observatory similar to TPF-C to detect a spectral feature similar to the "red edge" due to sunlight reflecting off a light-harvesting organism on another planet could be very difficult because... |
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Definition
1. the spectrum of the planet might be complicated due to absorption features due to several molecules in the planet's atmosphere
2. most of the light from the planet is likely to have scattered off of clouds that would cover a light-harvesting organism on the planet's surface
3. the small amount of light coming from the planet will make it difficult to measure the spectrum with high precision and high spectral resolution
4. the red edge is not a feature of cholorophyll, so even if the extrasolar light harvesting organisms use photosynthesis, they might not have the same spectral features, so we do not know what exactly we would be looking for
5. the light-harvesting organism may cover only a small fraction of the planet's surface |
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Term
| HW6 In the various formulations of the Drake equation, which terms could be measured with scientific observations within the next few decades? |
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Definition
1. Rate of star formation
2. Average number of potentially habitable planets per star with planets
3. Age of the universe or age of the galaxy |
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Term
| HW6 If we assume that the duration of time between the formation of Earth and an event occurring on Earth is indicative of the fraction of planets on which that event will occur, then... |
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Definition
1. We would reason that the fraction of habitable planets that give rise to some form of life is likely large.
2. We would reason that the fraction of planets that give rise to intelligent life is likely small. |
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Term
| HW6 In order for two civilizations to have had even the most basic conversation... |
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Definition
1. At least one civilization would need to survive for a time greater than twice the distance between civilizations divided by the speed of light
2. Both civilizations would need to be capable of transmitting across interstellar distances and choose to do so
3. The distance between civilizations would need to be separated by less than half the age of the universe times the speed of light |
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Term
| HW6 When choosing how to search for signals from an extraterrestrial civilization, astronomers have chosen to transmit and search for signals at optical and radio wavelengths because... |
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Definition
1. Radio waves require relatively little energy and there is a relatively low cosmic background at frequencies between 1,000 and 10,000 MHz
2. Radio waves penetrate through interstellar dust more easily than optical or infrared light
3. The Earth's atmosphere causes relatively little absorption at optical and radio wavelengths
4. There are very few natural sources that cause visible lasers, so a laser signal would stand out from cosmic background |
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