Astronomy Chapter 5 – Flashcards
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How a star forms
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1. A cloud contracts under gravity 2. A disk forms because angular momentum is conserved 3. Nuclear reactions begin and a star is born 4. Clumps form from static electricity 5. Planetesimals form from collisions 6. A wind blows from the central star
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The terrestrial planets are different from the giant planets because when they formed
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the inner Solar System was hotter than the outer solar system
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nuclear reactions require very high
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temperature and pressure
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T/F: A molecular cloud is held together by gravity
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true, most everything in the universe that is held together is done so by gravity
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T/F: Gravity and angular momentum are both important in the formation of planetary systems
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True, gravity causes the cloud to start to come together while the conversion of angular momentum ensures that the cloud will start to form a disk and eventually planets
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T/F: The solar system formed a giant cloud of dust and gas that collapsed under gravity
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true, all stars and most planetary systems are made this way
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Extrasolar planets have been deleted by the
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direct imaging method, transit method, spectroscopic radial velocity method, gravitational lensing method
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What is one advantage that allowed the four Jovian planets to collect massive gaseous atmospheres whereas the terrestrial planets could not
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jovian planet orbits are more widely spaced than terrestrial planet orbits
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Why is it so difficult of astronomers to take a picture of an extrasolar planet?
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1. stars are so distant that they appear only as point sources, as their planets are much smaller than the stars themselves 2. planets are fainter than their stars and cannot be seen in the glare of starlight
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Where is an accretion disk, and what are its characteristics?
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1. conservation of angular momentum leads a cloud to form a disk rather than collapse entireley 2. an accretion disks radius is typically hundreds of AU 3. the shape and motion of the accretion disk are the reason the subsequently formed planets all orbit in or near the equatorial plane of the star
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Which of the following are reasons that gravity is important to star and planet formation? (Choose all that apply.) ⓐ Gravity determines the direction in which the system rotates. ⓑ Gravity causes the cloud to collapse. ⓒ Without gravity, tiny dust particles would never come together to form larger particles. ⓓ Gravity causes the collapsing cloud to form a disk because it acts downward more strongly than it acts inward. ⓔ Once bodies are large enough, gravity pulls them together to make even larger bodies. ⓕ Gravity causes atmospheres to form around planetesimals.
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ⓑ Gravity causes the cloud to collapse. ⓔ Once bodies are large enough, gravity pulls them together to make even larger bodies. ⓕ Gravity causes atmospheres to form around planetesimals.
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When dust grains first begin to grow into larger objects, this occurs because of ⓐ gravity between dust grains. ⓑ gravity from the central star. ⓒ collisions between dust grains. ⓓ gravity from large planetesimals. ⓔ collisions of dust grains with large planetesimals.
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ⓒ collisions between dust grains.
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The direction of revolution in the plane of the Solar System was determined by ⓐ the plane of the galaxy in which the Solar System sits. ⓑ the direction of the gravitational force within the original cloud. ⓒ the direction of rotation of the original cloud. ⓓ the amount of material in the original cloud.
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ⓒ the direction of rotation of the original cloud.
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The terrestrial planets are different from the giant planets because when they formed, ⓐ the inner Solar System was richer in heavy elements. ⓑ the inner Solar System was hotter than the outer Solar System. ⓒ the outer Solar System took up a bigger volume, so there was more material to form planets. ⓓ the inner Solar System was moving faster, so centrifugal force was more important.
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ⓑ the inner Solar System was hotter than the outer Solar System.
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The radial velocity method preferentially detects ⓐ large planets close to the central star. ⓑ small planets close to the central star. ⓒ large planets far from the central star. ⓓ small planets far from the central star. ⓔ none of the above. (The method detects all of these equally well.)
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ⓐ large planets close to the central star.
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Planetary systems are probably ⓐ exceedingly common—nearly every star has planets. ⓑ common—many stars in our galaxy have planets. ⓒ rare—few stars have planets. ⓓ exceedingly rare—only one star has planets.
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ⓑ common—many stars in our galaxy have planets.
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Nuclear reactions require very high __________ and _________. ⓐ temperature; density ⓑ volume; density ⓒ density; area ⓓ mass; area ⓔ temperature; mass
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ⓐ temperature; density
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The transit method preferentially detects ⓐ large planets close to the central star. ⓑ small planets close to the central star. ⓒ large planets far from the central star. ⓓ small planets far from the central star. ⓔ none of the above. (The method detects all of these equally well.)
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ⓐ large planets close to the central star.
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Which of the following are true? An "Earth-like" planet ⓐ has life on it. ⓑ has water on it. ⓒ has physical properties similar to Earth's. ⓓ orbits a Sun-like star.
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ⓒ has physical properties similar to Earth's.
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A planet in the "habitable zone" ⓐ is close to the central star. ⓑ is far from the central star. ⓒ is the same distance from its star as Earth is from the Sun. ⓓ is at a distance where liquid water can exist on the surface. ⓔ is extremely rare—none have yet been found.
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ⓓ is at a distance where liquid water can exist on the surface.
