Melissa Beauvais Astronomy Study Guide Exam 3 Chapters 8-13 Chap 8: Which of the following statements best describes the general pattern of composition among the four jovian planets? Jupiter and Saturn have compositions that are fairly different from the compositions of Uranus and Neptune. Look at the densities of the jovian planets given in figure 1. Which of the following statements best describes the pattern of jovian planet densities? There is no clear trend in the densities. Which of the following statements best explains why the densities of Uranus and Neptune are higher than those of Jupiter and Saturn? They have a higher proportion of hydrogen compounds and rock. Which of the following best explains why Jupiter?s density is higher than Saturn's? Jupiter is more massive then Saturn Based on the leading scientific theory of solar system formation, which of the following statements best explains why Uranus and Neptune have a significantly different composition and higher density than Jupiter and Saturn? Jupiter and Saturn captured more gas from the solar nebula than Uranus and Neptune. The following images show Earth and the four jovian planets of our solar system. Rank these planets from left to right based on their distance from the Sun, from closest to farthest. (Not to scale.) Closest: Farthest: Earth Jupiter Saturn Uranus Neptune The following images show Earth and the four jovian planets of our solar system. Rank these planets from left to right based on their size (average equatorial radius), from smallest to largest. (Not to scale.) Smallest Radius: Largest Radius: Earth Neptune Uranus Saturn Jupiter The following images show Earth and the four jovian planets of our solar system. Rank these planets from left to right based on their mass, from lowest to highest. (Not to scale.) Lowest Mass: Highest Mass: Earth Uranus Neptune Saturn Jupiter Jupiter & Saturn only: Composed mostly of hydrogen and helium. -Interior is mostly liquid or metallic hydrogen. Uranus & Neptune only: Composed mostly hydrogen compounds. -Blue color because of methane. All four jovian planets: Approximately 10 Earth-mass core. -Strong atmospheric winds & storms. -Orbited by rings of ice & rock. -Magnetic field stronger than Earth?s. No jovian planets: Solid surface under a thick atmosphere. Which lists the jovian planets in order of increasing distance from the sun? Jupiter, Saturn, Uranus, Neptune Why does Neptune appear blue and Jupiter red? Methane in Neptune?s atmosphere absorbs red light Why is Jupiter denser than Saturn? Its higher mass & gravity compress its interior. Some jovian planets give off more energy than they receive because of? Ongoing contraction or differentiation 1. The largest moon in the solar system is Ganymede. 2. The jovian moon with the most geologically active surface is Io. 3. Strong evidence both from surface features and magnetic field data support the existence of a subsurface ocean on Europa. 4. Tidal heating is responsible for the tremendous volcanic activity on Io. 5. Callisto is the most distant of Jupiters four Galilean moons. 6. The fact that Europa orbits Jupiter twice every one orbit of Ganymede is an example of a (n) Orbital resonance. The main ingredients of most satellites of the jovian planets are? Hydrogen compound ices Why is Io more volcanically active than our moon? Io has a different internal heat source. What is unusual about Triton? It orbits its planet backward. Which moon shows evidence of rainfall & erosion by some liquid substance? Titan Saturn?s rings are composed of____. Lots of individual particles of ice & rock Saturn?s rings look bright because _____. Light from the sun reflects off the material in the rings. Which of the following statements correctly describes the motion of the particles in Saturn?s rings? Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings. Saturn?s rings.. Are continually supplied by impacts with small moons. CHAP 9 According to this graph, the minimum size of an object that could cause a mass extinction is a little less than _____. 10 km According to the graph, an object 10 kilometers across hits Earth __________. About once every 100 million years. What is the probability that an object 100 meters in diameter will hit Earth during the coming year? About 1 in 1000 Based on this graph, which statement below most accurately describes the impacts we should expect on Earth during the coming year? Earth will be hit by at least one object a few meters in diameter, along with many smaller objects. The impact of a 100-meter object will not cause "widespread" devastation, but it could still kill millions of people if it struck a major city. In Part C, you found that the probability of such an impact in any single year is only 1 in 1000. Suppose we learn that it has already been 1200 years since the last such impact. What would that tell us? Nothing; we would still presume that the chance of such an impact during the next year is 1 in 1000. The asteroid belt lies between the orbits of Mars and Jupiter Jupiter nudges the asteroids through the influence of Orbital resonances Can an asteroid be pure metal? Yes, it must have been the core of a shattered asteroid. What does Pluto most resemble? A Comet CHAP 10 Following are the different layers of the Sun?s atmosphere. Rank them based on the order in which a probe would encounter them when traveling from Earth to the Sun?s surface, from first encountered to last. First encountered: Last encountered: Corona Chromosphere Photosphere Rank the layers of the Sun?s atmosphere based on their density, from highest to lowest. Highest Density: Lowest Density: Photosphere Chromosphere Corona Rank the layers of the Sun?s atmosphere based on their temperature, from highest to lowest. Highest Temperature: Lowest Temperature: Corona Chromosphere Photosphere Rank the layers of the atmosphere based on the energy of the photons that are typically emitted there, from highest to lowest. Highest energy of the photons: Lowest energy of the photons: Corona Chromosphere Photosphere Which of the following changes would cause the fusion rate in the Sun?s core to increase? An increase in the core temperature A decrease in the core radius Which of the following must occur for a star?s core to reach equilibrium after an initial change in fusion rate? If the fusion rate initially increases, then the core expands. If the fusion rate initially decreases, then the core contracts. What would happen if the fusion rate in the core of the Sun were increased but the core could not expand? The Sun?s core would start to heat up and the rate of fusion would increase even more. 1. Nuclear fusion of hydrogen into helium occurs in the core. 2. Energy moves through the sun?s convection zone by means of the rising of hot gas and falling of cooler gas. 3. Nearly all the visible light we see from the sun is emitted from the photosphere. 4. Most of the sun?s ultraviolet light is emitted from the narrow layer called the chromosphere where temperature increases with altitude. 5. We can see the Sun?s corona most easily during total solar eclipses. 6. The radiation zone is the layer of the sun between its core and convection zone. To understand the interplay of observations and models you must first be able to distinguish between things that we observe and things that we infer from models. Consider the following statements about the Sun. Classify each statement as an observation or as an inference based on the current, accepted model for the Sun. Observations: -The corona is hotter than the photosphere. -The photosphere emits mostly visible light. -The photosphere is made mostly of hydrogen & helium. -The sun emits neutrinos. Inferences from a model: -The composition of the photosphere is the same as that of the gas cloud that gave birth to our solar system. -The sun generates energy by fusing hydrogen into helium in its core. -The convection zone is cooler than the radiation zone. -The core temperature is 10 million K. Which of these groups of particles has the greatest mass? Four individual protons Solar energy leaves the core of the sun in the form of? Photons How does the number of neutrinos passing through your body at night compare with the number passing through your body during the day? About the same Listed following are events or phenomena that occur during either the part of the sunspot cycle known as solar minimum or the part known as solar maximum. Match these items to the correct part of the sunspot cycle. Solar Maximum: -Solar flares are most common. -Orbiting satellites are most at risk. -Occurs about 11 years after a solar maximum (on average). -Sunspots are most numerous on the sun. -Auroras are most likely in Earth?s skies. Solar Minimum: -Occurs about 5 to 6 years after a solar maximum (on average). Why do sunspots appear darker than their surroundings? They are cooler than their surroundings Which of these things poses the greatest hazard to communications satellites? Particles from the sun. What causes the cycle of solar activity? Changes in the organization of the sun?s magnetic field. 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? It predicted that the sun could shine for about 25 million years, but geologists had already found that earth is much older than this. The arrows in this diagram are meant to show how gravitational equilibrium works in the Sun. What do the different colors and different arrow lengths represent? Green arrows represent gravity; red arrows represent pressure; longer arrows represent a stronger push or pull. What layer of the sun are we seeing in this photo? Photosphere The dark spots in this photo (such as the one indicated by the arrow) represent what we call: Sunspots Which photo shows earth correctly scaled in comparison to the sun? This photograph shows a small portion of the Sun's photosphere. What is going on in the bright regions (such as the bright region indicated by the arrow)? Hot gas is rising up from the solar interior This X-ray image shows a loop of hot gas above the surface of the Sun. If we took a visible light photo that looked in the Sun's photosphere just under the two points where the loop of gas comes down (arrows), what would we find? Sunspots Look again at the loop of hot gas in this X-ray image. Suppose we took another photo looking at the same place one hour later. What would we see? The loop would look about the same as it does in this photo What layer of the Sun are we seeing in this photograph, and in what wavelength band was it photographed? Corona, photographed in X rays What do the yellow regions represent in this photograph?^^^^(Same photo as above) Regions where very hot gas is emitting a lot of X rays Study this figure and its axis labels. What is this graph showing us? The number of sunspots on the Sun tends to increase and decrease with an approximately 11-year cycle. CHAP 11 Before we can use parallax to measure the distance to a nearby star, we first need to know __________. The earth-sun distance. Which of the following is a valid way of demonstrating parallax for yourself? Hold up your hand in front of your face, and alternately close your left and right eyes. What is the cause of stellar parallax? Earth?s orbit around the sun. The more distant a star, the Smaller its parallax angle Approximately what is the parallax angle of a star that is 20 light-years away? 0.16 arcsecond Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years? 3.3 light-years If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would Get smaller What do we need to measure in order to determine a star?s luminosity? Apparent brightness and distance. Listed following are several fictitious stars with their luminosities given in terms of the Sun?s luminosity () and their distances from Earth given in light-years (). Rank the stars based on how bright each would appear in the sky as seen from Earth, from brightest to dimmest. If two (or more) stars have the same brightness in the sky, show this equality by dragging one star on top of the other(s). Brightest: Dimmest: Nismo:100Lsun, 8 lyShelby: 100Lsun, 10 lyEnzo: 200Lsun, 20 lyLotus: 400Lsun, 40 ly Ferdinand: 400Lsun, 20 ly Listed following is the same set of fictitious stars given in Part A. Rank the stars based on how bright each would appear in the sky as seen from Jupiter, from brightest to dimmest. Brightest: Dimmest: Nismo:100Lsun, 8 lyShelby: 100Lsun, 10 lyEnzo: 200Lsun, 20 lyLotus: 400Lsun, 40 ly Ferdinand: 400Lsun, 20 ly For stars of the same luminosity, apparent brightness decreases with distance (following the inverse square law for light). Therefore, the star that appears dimmest must be the most distant and the star that appears brightest must be the nearest. Remember that this is true ONLY if you know that all stars have the same intrinsic luminosity. Because there is no way to know luminosity just by looking at a star in the sky, you cannot in general use brightness to say anything about distance. Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________. Less luminous, cooler, smaller, and less massive. Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________. Cooler and larger in radius Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________. Hotter and smaller in radius Notice that the stars in the lower left of the diagram are called white dwarfs: white because they are hot enough to appear ?white hot? to our eyes, and dwarfs because of their small sizes. A typical white dwarf is no larger in size (radius) than our Earth, but has as much mass as the Sun. - The main-sequence lifetime is greater for low-mass stars than it is for high-mass stars. - The stars known as supergiants are the very largest and brightest of all the stars. -Most of the stars near the sun are main-sequence stars. - Stars are classified on the basis of their spectral type and luminosity class. - Cepheids are examples of pulsating variable stars. -White dwarfs are no longer generating energy through nuclear fusion. -Stars that are cooler than the sun yet 100 to 1,000 times as luminous as the sun are classified as Giants. Which of these stars has the coolest surface temperature? a K star Which of these stars is the most massive? A main-sequence A star Which of these stars has the longest lifetime? A main-sequence M star Consider a relatively nearby, single star, that is, a star that is not a member of a binary system and has no known orbiting planets. Listed below are a few properties of this star. Classify each property as either something that we can observe or measure directly (with the aid of a telescope and instruments such as cameras or spectrographs) or something that we must infer indirectly (and hence is correct only if all of our assumptions are correct). Observe Directly: -Apparent brightness -Color -Parallax angle -Spectral type Infer Indirectly: -Luminosity -Mass -Radius -Surface temperature From Part A, you know that surface temperature is a stellar property that we infer indirectly. What must we measure directly so that we can infer a star?s surface temperature? Spectral type Which of the following must be true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light? We have measured the star?s distance. We have measured the star?s apparent brightness. No interstellar gas or dust absorbs or scatters light between us and the star. We found that mass must be inferred for the star described in Part A. However, we can measure a star?s mass directly if __________. It is a member of an eclipsing binary system You should now see that the reason the mass of the star in Part A must be inferred is that the star has no known orbiting objects, which means we cannot apply Newton?s version of Kepler?s third law. Which of the following must be true if the star?s inferred mass is to be accurate? We have determined that the star is a main-sequence star We have measured the star?s spectral type. Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest. Highest temperature: Lowest temperature: A Blue white Sun An orange main- A red supergiant star dwarf star sequence star Notice that temperature is related to color, and follows the order of the colors in the rainbow: Blue (or violet) stars are the hottest, while red stars are the coolest. In the parts that follow, the H-R diagrams show the correlation between color and temperature on the horizontal axis. All five stars appear at the same place along the horizontal axis showing spectral type. Because spectral type is related to surface temperature, all five stars must have the same surface temperature. Now proceed to Part C to determine how these stars vary in luminosity. Luminosity is shown along the vertical axis, with stars higher up more luminous than those lower down. Note that each tickmark along the luminosity axis represents a change by a factor of 10 from the prior tickmark, so the range of luminosities is quite large. Continue to Parts D and E to investigate surface temperature and luminosity for a different set of five stars. Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M having the lowest surface temperature. In other words, spectral type increases to the left on the H-R diagram. Now proceed to Part E to determine how these stars compare in luminosity. All five stars have the same luminosity because they are all at the same height along the vertical (luminosity) axis. Continue to Parts F and G for more practice in reading surface temperature and luminosity on the HR diagram. All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star? Its mass and its stage of life Based on the definition of apparent brightness, which units are appropriate for its measurement? Watts per square meter Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore: Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A. Luminosity is an intrinsic property, so two identical stars will always have the same luminosity. But apparent brightness follows an inverse square law with distance, so the fact that Star A is twice as far away makes it 22 = 4 times dimmer. A star with a parallax angle of 1/20 arcsecond is? 20 parsecs away This is true because distance in parsecs = 1/(parallax angle in arcsecond). Note that 20 parsecs is equivalent to 20 × 3.26 = 65.2 light-years. The star Vega has an absolute magnitude of about 4 and an apparent magnitude of about 0. Based on the definitions of absolute and apparent magnitude, we can conclude that ______. Vega is nearer than 10 parsecs from earth. Which of the following statements about spectral types of stars is not generally true? The spectral type of a star can be used to determine its distance. Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude? Rigel has a higher surface temperature than Sirius To calculate the masses of stars in a binary system, we must measure their _________. Orbital period and average orbital distance 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 _________ The star is a member of an eclipsing binary star system You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star's _________. Mass The approximate main-sequence lifetime of a star of spectral type O is______. 3 million years How did astronomers discover the relationship between spectral type and mass for main sequence stars? By measuring the masses and spectral types of main-sequence stars in binary systems. The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is the youngest? The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants. 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? The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs. CHAP 12 The following figures show the spectral types of four main-sequence stars. Rank them based on the time each takes, from longest to shortest, to go from a protostar to a main-sequence star during the formation process. Longest time: Shortest time: M6 G2 A5 O9 Notice that the correct ranking has the stars in order from lowest to highest mass (remember that for main-sequence stars, mass follows the spectral sequence order OBAFGKM). Less massive stars take longer to go through all stages of life than do more massive stars, so they also take longer to reach the main sequence. Practice Exam 3 Chap 8 concept quiz Which of the following gases is not a significant of the jovian planet atmosphere? Carbon dioxide Jupiter and the other jovian planets are sometimes called "gas giants." In what sense is this term misleading? They actually contain relatively little material in a gaseous state. What would happen to Jupiter if we could somehow double its mass? Its density would increase but its diameter would barely change. According to our theory of solar system formation, why did Uranus and Neptune end up to be much less massive than Jupiter and Saturn? Particles in the solar nebula were more spread out at greater distances, so that accretion took longer and there was less time to pull in gas before the solar wind cleared the nebula. Why does Jupiter have three distinct layers of clouds? The three layers represent clouds made of gases that condense at different temperatures. Which of the following best why we see horizontal "stripes" in photographs of Jupiter and Saturn? The light stripes are regions of high clouds, and the dark stripes are regions where we can see down to deeper, darker clouds. And the reason these stripes stretch all the way around these planets is the strong Coriolis force that comes from the planets' rapid rotation Uranus and Neptune have methane clouds but Jupiter and Saturn do not. Which factor explains why? Temperatures on Jupiter and Saturn are too high for methane to condense But methane can condense on Uranus and Neptune because they are farther from the Sun and hence colder. Which jovian planet should have the most extreme seasonal changes? Uranus Its large axis tilt gives it seasons that each last about one quarter of its 84-year orbit Why is the radiation so intense in the region that traces Io's orbit around Jupiter (the Io torus)? The region is full of gases that become ionized after they are released from volcanoes on Io. Io?s low gravity allows these gases to escape Which of the following best explains why many jovian moons have been more geologically active than the Moon or Mercury? Jovian moons are made mostly of ice that can melt or deform at lower temperatures than can the rock and metal that make up the Moon and Mercury. That is why icy worlds need far less internal heat for geological activity than rocky worlds. All the following statements are true. Which one is most important in explaining the tremendous tidal heating that occurs on Io? Io orbits Jupiter on an elliptical orbit, due to orbital resonances with other satellites. On an elliptical orbit, tides vary and flex Io?s shape Which of the following is not a piece of evidence supporting the idea that Europa may have a subsurface ocean? Astronomers have detected small lakes of liquid water on Europa's surface. There is no evidence of liquid water on Europa's surface, and even if liquid water emerged the cold temperatures would ensure that it would quickly freeze. Which of the following is most unlikely to be found on Titan? Lakes of liquid water in the warmer equatorial regions Titan's surface temperature is never anywhere close to being warm enough for liquid water, even at its equator. Why do astronomers believe that Triton is a captured moon? Triton orbits Neptune in a direction opposite that of Neptune's rotation. This ?backward? orbit is a tell-tale sign of a captured moon Which statement about Saturn's rings is not true? The rings must look much the same today as they did shortly after Saturn formed. Ring particles cannot last long compared to the age of the solar system, so the rings much change their appearance with time. According to current understanding, which of the following is required in order for a planet to have rings? The planet must have many small moons that orbit relatively close to the planet in its equatorial plane Ring particles come from small and large impacts on these small moons. Chap 9 Concept Quiz Which of the following statements is not true? Objects in the Kuiper belt are made mostly of rock and metal. Kuiper belt objects contain large amounts of ice; in fact, many comets that enter the inner solar system come from the Kuiper belt. A rock found on Earth that crashed down from space is called ______ A meteorite The asteroid belt is located ___ Between the orbits of Mars and Jupiter Which statement about asteroids is not true? If we could put all the asteroids together, they would make an object about the size of Earth. The total mass of the asteroids is much less than the mass of a terrestrial planet. A typical meteor is created by a particle about the size of a ___ Pea We do not see the particle itself, but rather the flash of light it generates as it enters (and burns up in) the atmosphere at high speed. What do we mean by a primitive meteorite? a piece of rock that is essentially unchanged since it first condensed and accreted in the solar nebula some 4.6 billion years ago Among discovered meteorites, we have found some with all the following origins except ______ Being a fragment from comet Halley No such fragments are known and they are unlikely to exist, since comet fragments should be ice that would burn up as they passed through our atmosphere. Which statement is not thought to be true of all comets in our solar system? Comets always have tails. Only rare comets that enter the inner solar system have tails, and only when they are close to the sun. Which direction do a comet's dust and plasma tails point? Generally away from the sun. they are pushed away from the sun by radiation and the solar wind. When a comet passes near the Sun, part of it takes on the appearance of a large, bright ball from which the tail extends. This part is called _________. The coma. Coma is essentially a large atmosphere of gas and dust released by the comet. The total number of comets orbiting the Sun is estimated to be about ________ 1 trillion What is Charon? The largest of Pluto?s three known moons According to current evidence, Pluto is best explained as ______. A large member of the Kuiper belt What is Eris? An icy object that orbits in the Kuiper belt and is larger than Pluto What was the Shoemaker-Levy 9 impact? the 1994 impact of a chain of comet fragments into Jupiter What do we mean by a mass extinction? the extinction of a large fraction of the world's plant and animal species in a relatively short period of time If the hypothesis tracing the extinction of the dinosaurs to an impact is correct, the dinosaurs died off largely because ______. of global climate effects initiated by dust and smoke that entered the atmosphere after the impact Chap 10 Concept Quiz According to modern science, approximately how old is the Sun? 4 ½ billion years The Sun will exhaust its nuclear fuel in about ______. 5 billion years Which of the following correctly describes how the process of gravitational contraction can make a star hot? When a star contracts in size, gravitational potential energy is converted to thermal energy What two physical processes balance each other to create the condition known as gravitational equilibrium in stars? Gravitational force and outward pressure The source of energy that keeps the Sun shining today is _________. Nuclear fusion Energy balance in the Sun refers to a balance between _________. the rate at which fusion generates energy in the Sun's core and the rate at which the Sun's surface radiates energy into space When we say that the Sun is a ball of plasma, we mean that _________. The Sun consists of gas in which many or most atoms are ionized (missing electrons). What is the Sun made of (by mass)? 70% hydrogen, 28% helium, 2% other elements From center outward, which of the following lists the "layers" of the Sun in the correct order? core, radiation zone, convection zone, photosphere, chromosphere, corona What are the appropriate units for the Sun's luminosity? Watts The Sun's surface, as we see it with our eyes, is called the _________. Photosphere The Sun's average surface (photosphere) temperature is about ______. 5,800K What is the solar wind? a stream of charged particles flowing outward from the surface of the Sun The solar wind blows outward in all directions and has important effects on the planets, especially through interactions with planetary magnetospheres. The fundamental nuclear reaction occurring in the core of the Sun is _________. Nuclear fusion of hydrogen into helium The proton-proton chain is _________. It is the specific set of nuclear reactions through which the Sun fuses hydrogen into helium. The overall result of the proton-proton chain is: 4H Becomes 1 He + energy To estimate the central temperature of the Sun, scientists _________. use computer models to predict interior conditions Why are neutrinos so difficult to detect? They have a tendency to pass through just about any material without any interactions. The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about _________. A few hundred thousand years ago What happens to energy in the Sun's convection zone? Energy is transported outward by the rising of hot plasma and sinking of cooler plasma. What do sunspots, solar prominences, and solar flares all have in common? They are all strongly influenced by magnetic fields on the sun. Which of the following is not a characteristic of the 11-year sunspot cycle? The sunspot cycle is very steady, so that each 11-year cycle is nearly identical to every other 11-year cycle. How is the sunspot cycle directly relevant to us here on Earth? Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment. Chap 11 Concept Quiz What is the approximate chemical composition (by mass) with which all stars are born? three quarters hydrogen, one quarter helium, no more than 2% heavier elements The total amount of power (in watts, for example) that a star radiates into space is called its _________. Luminosity According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples? Its apparent brightness will decrease by a factor of 9 Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do? Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity. If star A is closer to us than star B, then Star A's parallax angle is ______ Larger than that of star B Ten parsecs is about____ 32.6 light-years You find this by remembering that 1 parsec = 3.26 light-years 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 From hottest to coolest, the order of the spectral types of stars is _________. OBAFGKM (Oh Be A Fine Girl Kiss Me) Our Sun is a star of spectral type ______ G Because the spectral sequence is OBAFGKM, the Sun's spectral type of G means that the Sun's surface is hotter than that of K and M stars, but cooler than that of O, B, A, and F 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 Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts? Spectroscopic binary The axes on a Hertzsprung-Russell (H-R) diagram represent _______ Luminosity and surface temperature What can we infer, at least roughly, from a star's luminosity class? Its size (radius) On an H-R diagram, stellar radii ________ Increase diagonally from the lower left to the upper right Small radius white dwarfs are down near the lower left, while large radius supergiants are in the upper right On an H-R diagram, stellar masses _________ can be determined for main sequence stars but not for other types of stars How is the lifetime of a star related to its mass? More massive stars live much shorter lives than less massive stars. Each choice below lists a spectral type and luminosity class for a star. Which one is a red supergiant? Spectral type M2, luminosity class I Spectral type M means the star is cool and red, and luminosity class I means it is a supergiant. What is the common trait of all main sequence stars? They generate energy through hydrogen fusion in their core. A star becomes a main-sequence star when it first starts fusing hydrogen into helium, and it ends its main-sequence life when it exhausts its central core supply of hydrogen for fusion. Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true? Earth would be inside the supergiant What is a white dwarf? the remains of a star that ran out of fuel for nuclear fusion Once the nuclear fuel runs out, the star can no longer shine; for relatively low-mass stars, gravity then compresses its remaining core into a white dwarf. Which of the following statements comparing open and globular star clusters is not true? Open and globular clusters each typically contain a few hundred stars. Globular clusters contain many more stars than open clusters. What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us? It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age. Chap 12 Concept Quiz The dark area stretching from the center of this picture to the upper right is about 50 light-years long and lies in the plane of the Milky Way Galaxy. What is it? A star-forming cloud The main photo and the smaller inset both show the same field of view containing a star-forming molecular cloud. One of the photos was taken in visible light and the other in infrared light. Which one is the infrared photo, and how do you know? The main (larger) photo is the infrared one, which we can tell because molecular clouds emit infrared light but not visible light. This is the HR diagram for stars in a 12-billion-year-old globular cluster. Based on our understanding of stellar lives, which of the four labeled stars is currently generating energy through hydrogen fusion in a shell around an inert (non-burning) helium core. III This is a red giant, which means it has exhausted its core hydrogen (and left the main sequence) and is now generating energy through hydrogen fusion in a shell around the inert core. This Hubble Space Telescope photo shows a planetary nebula. What is the white dot in the center (indicated by the arrow)? A white dwarf Suppose a particular star has a core that is undergoing several stages of fusion simultaneously, as shown in this diagram. Based on your understanding of stellar lives, the mass of this star is probably: About 10 (or more) solar masses Suppose a particular star has a core that is undergoing several stages of fusion simultaneously, as shown in this diagram. Which of the following statements about this star is most likely to be true? (same image as above) The star will explode as a supernova within a few days. According to this diagram, how much more abundant is hydrogen in the universe than nitrogen? hydrogen is about 10,000 times as abundant as nitrogen This photo shows the famous Crab Nebula. What is it? An expanding cloud of remains from a star that died in a supernova. The arrow in the photo on the left shows the star that we see as a supernova in the photo on the right. What can we conclude about this star? It was a high-mass star with at least 8 times the mass of the Sun. Suppose you had looked with your naked eye at the supernova on the night it was photographed in the "after" photo. Assuming that it was bright enough to see (it was), what would it have looked like to your naked eye? (same photo as above) Like a single star in the night sky Chap 13 Concept Quiz A white dwarf is? What most stars become when they die A typical white dwarf is _________. as massive as the Sun but only about as large in size as Earth If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh _________. As much as a truck The maximum mass of a white dwarf is _________. About 1.4 times the mass of our sun What is an accretion disk? a disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole According to our modern understanding, what is a nova? an explosion on the surface of a white dwarf in a close binary system Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit? The white dwarf will explode completely as a white dwarf supernova A neutron star is? The remains of a star that died in a massive star supernova (if no black hole was created) A typical neutron star is more massive than our Sun and about the size (radius) of _________. A small asteroid (10 km in diameter) If you had something the size of a sugar cube that was made of neutron star matter, it would weigh _________. About as much as a large mountain Pulsars are thought to be____ Rapidly rotating neutron stars How is an X-ray burst (in an X-ray binary system) similar to a nova? Both involve explosions on the surface of stellar corpse. What is the basic definition of a black hole? an object with gravity so strong that not even light can escape Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly _________. 3 solar masses What do we mean by the event horizon of a black hole? It is the point beyond which neither light nor anything else can escape. Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit? Nothing-Earth?s orbit would remain the same. What do we mean by the singularity of a black hole? It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions. What makes us think that the star system Cygnus X-1 contains a black hole? It emits X rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star. The Schwarzschild radius of a black hole depends on _______ Only the mass of the black hole Based on current evidence, which of the following statements about gamma ray bursts is true? All those that we have detected occurred in distant galaxies. Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.
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