ASTRONOMY 3 - Nature of the Universe Fall 1998, 2nd Midterm Instructor: Prof. Amri Wandel Exam time is 1 hour. IMPORTANT: don't forget to fill in your name, ID AND test version (A, B or C) in the "bubbles" on the back of the scantron form. Good Luck! 1. Compared to that of Earth, the mass of Jupiter is A) About 11 times as large B) About 300 times larger C) Several thousand times larger D) About 1/300, because of Jupiter's low density 2. The rotation periods for the Jovian planets Jupiter, Saturn, Uranus, and Neptune are A) Very short, about 10 to 20 hours B) Reasonably long, on the order of several Earth days C) Very short, between 1 and 2 hours D) Very long, on the order of years, because of the sizes of these planets 3. The Great Red Spot is A) The colored polar cap of Jupiter B) Clouds of dust-laden gas upwelling above the top of a massive mountain or a volcano on the planet's surface C) A temporary storm in Jupiter's atmosphere, lasting a few months D) A large, long-lived high-pressure storm in Jupiter's atmosphere 4. What causes the banded structure on Jupiter's visible "surface"? A) An underlying rising and falling convection pattern stretched into bands by Jupiter's rapid rotation B) An underlying north-south flow pattern stretched into bands by Jupiter's rapid rotation C) The "sweeping" of Jupiter's clouds through magnetic field lines from Jupiter's magnetosphere D) The breaking up of strong eastward flow due to Jupiter's rapid rotation by underlying mountain ranges 5. The major components of the visible surfaces of the Jupiter and Saturn atmospheres, other than hydrogen and helium, have been found to be A) CH4 (methane), NH3 (ammonia), H2O (water) B) Dust and iron oxides C) H2O (water), CO2 (carbon dioxide) D) N2 (nitrogen), O2 (oxygen), CO2 (carbon dioxide) 6. Jupiter appears as a flattened, oblate spheroid in the sky because A) It was formed in this way at the time of planetary formation, and has solidified to this shape. B) It is moving rapidly around its orbit, flattening its shape. C) Tidal distortion from its moons and from the Sun have distorted its shape. D) It is spinning rapidly and is composed mostly of fluid matter. 7. The internal structure of the two largest Jovian planets (from center outward) is A) Rocky core, liquid molecular hydrogen layer, liquid metallic hydrogen layer B) Iron-nickel core, rocky mantle, solid crust C) Rocky core, liquid methane mantle, gaseous methane atmosphere D) Rocky core, liquid metallic hydrogen layer, liquid molecular hydrogen layer 8. The material in the interiors of Jupiter and Saturn that is thought to be responsible for their powerful magnetic fields is A) Gases of NH3 (ammonia), CH4 (methane), and H2O (water vapor) B) Liquid metallic hydrogen C) Solid magnetic iron D) Molten iron and nickel 9. What conditions are considered to be necessary for a planet to be able to generate an intense magnetic field? A) Electrically conducting material in its interior and slow rotation, because rapid rotation will destroy a magnetic field B) A solid iron core into which a magnetic field was induced early in the planet's history C) Relatively rapid rotation and electrically conducting material in its interior D) An ionized and electrically conducting layer in its atmosphere 10. The magnetosphere of Jupiter is A) A doughnut-shaped region similar to the Van Allen belts around the Earth containing high-speed protons and electrons whose motions produce the planet's magnetic field B) A large cavity created and maintained within the solar wind stream by the planet's magnetic field, filled with extremely hot ionized plasma C) A narrow layer in which intense electric currents flow, just above the cloud tops in the planet's atmosphere, generating the planet's magnetic field D) The inner regions of Jupiter just outside the solid core that contain liquid metallic hydrogen, in which electric currents flow to produce the planet's magnetic field 11. What is significant about the rotational and revolutional motions of the Galilean moons of Jupiter and of our own Moon? A) Nonsynchronous rotation, with axes of rotation in any direction with respect to their orbital plane B) Nonsynchronous rotation, with independent periods of rotation and revolution, and spin axes perpendicular to orbit C) Synchronous rotation, with one face always pointed toward the Sun D) Synchronous rotation, with one face always pointed toward the planet 12. The moons of Jupiter behave in which way, in terms of the relationship between the period P and radius a of their orbits around the planet? A) They obey the Keplerian relation, P2 = ka3, in which k is the same as that for planetary motion around the Sun, because it is a universal constant B) The moons do not obey the Keplerian relation P2 = ka3, because they orbit Jupiter and not the Sun C) The moons do not obey the Keplerian relation P2 = ka3, because their motion about Jupiter is affected by Jupiter's motion about the Sun D) They follow a Keplerian relationship, P2 = ka3, where k is a constant that is different from that in the relation governing planetary motion around the Sun. 13. How would Interplanetary Travel advertise a holiday on Jupiter's satellite Io? A) Glaciers galore for your hiking pleasure under star-studded skies! B) Hot and dry—never rains—beautiful sulfurous skies! C) The largest number of volcanoes for your travel dollar anywhere in the Solar System! D) Exquisite ethane lakes, hydrocarbons beyond your wildest dreams! 14. The heating of the interior of Io, the innermost Galilean moon of Jupiter, is caused by A) Thermal heating from Jupiter, because Jupiter emits more radiation than it receives from the Sun B) Continuous tidal distortion by Jupiter and the other moons C) Continual bombardment by meteoroids, attracted by Jupiter's enormous gravitational pull D) The fact that Io moves inside Jupiter's magnetosphere, where the temperature is as high as anywhere in the solar system 15. How is the Io plasma torus formed? A) Io disturbs Jupiter's magnetosphere, causing magnetospheric charged particles to collect in a ring around Io's orbit. B) Io's volcanic plumes eject atoms into orbit around Jupiter, where they are then ionized by high-energy charged particles in Jupiter's magnetosphere. C) Io's motion through Jupiter's magnetosphere creates currents of electrons and charged particles in a loop between Io and Jupiter's north and south magnetic poles. D) Charged particles from Jupiter's magnetosphere knock atoms out of Io's surface and volcanic plumes and ionize them. 16. The surface of Europa, one of the Galilean moons of Jupiter, appears to be covered with A) A smooth layer of ice, crossed by many cracks B) Rugged mountain ranges and ancient volcanoes C) Dark areas of older crust separated by lighter, grooved terrain D) Many ancient craters and maria 17. The largest satellite (moon) in our planetary system is A) Phobos, one of the moons of Mars B) Earth's Moon C) Titan, a moon of Saturn D) Ganymede, a moon of Jupiter 18. The mean thickness of Saturn's rings is now thought to be A) A few tens of meters B) About 10,000 meters C) A few kilometers D) A few thousands of meters 19. The main gravitational effect that organizes the particles in the rings of Saturn into specific orbits is A) The perturbing effects of neighboring planets, such as Jupiter and Neptune B) Collisions between the major moons of the planets and the ring particles at the same orbital distance, clearing gaps in the rings C) The complex gravitational tidal effects of the planet and the Sun upon the ring particles D) The perturbing effects of major and minor moons or satellites whose orbital periods are related to those of the ring particles by simple ratios (for example, 2:1, 3:2) 20. What would be a typical weather forecast on Titan, Saturn's largest moon? A) Turbulent winds in an ammonia, methane, and water vapor atmosphere, with dense clouds of ammonia compounds and water ice B) Hydrocarbon fog and ethane rain in a nitrogen atmosphere C) Occasional sulfur clouds and sulfur dioxide fog, from volcanic eruptions D) Dust storms and high winds in a thin CO2 atmosphere 21. The rings of Saturn are composed of very many small particles because A) They were formed by the impact of a fast-moving asteroid on a large moon that broke up into very many pieces. B) They are made up of ice and ice-coated rocks that break up easily in sunlight. C) They were spun out of the planet under its rapid rotation over a long period of time. D) They are inside the Roche limit of Saturn, where tidal forces are stronger than the mutual gravitational forces between particles. 22. Why is the F ring much narrower than the main rings? A) The ring is constrained by Saturn's strong magnetic field. B) Two "shepherd" satellites focus the particles into a narrow ring. C) The ring is in a stronger part of Saturn's gravitational field and cannot spread out any farther. D) There are not enough particles available to make a wider ring. 23. What is the interior structure of Saturn? A) A thick mantle of liquid hydrogen with a rocky core and a relatively thin, gaseous atmosphere B) A thick, gaseous atmosphere over a thin mantle of liquid hydrogen and a rocky core C) A large, rocky core with a very thin mantle of liquid hydrogen and a thin, gaseous atmosphere D) A large, liquid hydrogen core overlain by a thin, gaseous atmosphere 24. How was Neptune discovered? A) By accident, by an astronomer who was conducting a sky survey B) By a careful search in the 1930s by an astronomer who was convinced it must be there C) By an astronomer studying old photographs of the sky, several years after they were taken D) By careful application of Newton's laws to the motion of other planets 25. Seasonal variations at a particular point on Uranus during a Uranian year would be A) Not present at any point on the planet, because dense clouds shield it from climate changes B) Nonexistent, because such variations at any point on the planet will be smoothed out during its long "year" by the planet's rapid rotation C) Almost nonexistent, because Uranus moves in an almost perfectly circular orbit and its distance from the Sun remains constant D) Extreme, because its spin axis is nearly in its orbital plane 26. The atmospheres of Uranus and Neptune consist of A) Mostly hydrogen and helium, with significant amounts of methane, ammonia and water vapor B) Mostly methane, with small quantities of hydrogen and helium C) Mostly carbon dioxide, with a small amount of nitrogen D) Mostly hydrogen and helium, with significant amounts of methane and water vapor but very little ammonia 27. The ring system around Uranus was originally discovered by what observing technique? A) Occultation of light from a star as Uranus (and the rings) passed in front of it B) Radar reflection from the particles in the rings C) Infrared observation from the IRAS spacecraft in Earth orbit D) Observation by the cameras on board the Voyager 1 spacecraft 28. Triton, the giant moon of Neptune, differs from all other major moons of planets in that A) It orbits in a retrograde way, opposite to the planet's rotation. B) Its orbit takes it over the planet's poles. C) Its orbit is very elliptical. D) Its orbit lies inside that of the rings of Neptune. 29. Bode's law for the planets in the solar system provides the sequence of A) Sidereal periods of the planets as they orbit the Sun B) The semimajor axes, or mean orbital radii, of the orbits of the planets around the Sun C) Synodic periods of the planets as observed from the Earth D) Physical radii of the planets, from smallest to largest 30. How would a typical asteroid appear on a time exposure photograph of the sky as it orbited the Sun, if the camera were tracking the background stars? A) It would look like any other star, a small extra dot not shown on star charts of this area of the sky. B) It would look like a small, diffuse patch against the sharp images of stars because of the dust and gas surrounding it. C) It would produce a short trail as it moved slowly against the background stars. D) It would produce a flash of light as it crossed the field of view of the camera. 31. What is the relationship between the Kirkwood gaps in the asteroid belt and the Cassini and Enke divisions in the rings of Saturn? A) Both were discovered by observers from the same group; Kirkwood and Enke worked at the Cassini Observatory. B) Both are caused by selective melting of material at these specific locations from the central radiating body, the Sun and Saturn respectively. C) Both are caused by disruptions of orbits of small objects by a larger object whose orbital period is a simple ratio of that of the small objects. D) Both are caused by large objects passing through swarms of smaller objects, sweeping out gaps in the swarms. 32. Which of the following types of meteoroids is expected to be most common in the solar system? A) Carbonaceous chondrites B) Irons C) Stones D) Stony-irons 33. Most comet nuclei are believed to be A) Chunks of water and methane ice ejected from the surface of the icy satellites of the outer planets by asteroid impacts B) Chunks of dusty ice left over from the formation of the solar system C) Large carbon chondrite meteoroids that have been set on fire by the Sun and are trailing long smoke trails D) Chucks of rock or iron chipped from asteroids by impacts 34. A meteor shower, the appearance of greater than average numbers of "shooting stars" at a particular time in the year from a specific sky direction, is related to which astronomical phenomenon? A) The Earth's passage through part of the asteroid belt B) The passage of Earth through intense streams of solar material, including dust particles, during regular solar activity C) The passage of Earth through the remnants of an old comet D) The Earth's passage through different parts of the spiral arms of the Galaxy 35. What causes the granular appearance of the surface of the Sun? A) Thermonuclear fusion in its interior B) Convective motion under the solar surface C) The regular impact of meteoroids and comets onto the solar surface D) Differential rotation of the surface layers 36. The center of the disk of the visible Sun appears brighter than the edges because A) Cooler sunspots are more visible at the Sun's edge than they are at the center of the disk. B) We see into deeper and cooler layers at the center of the solar disk. C) We see a greater contribution from the corona of the Sun at the center of the disk. D) We see into deeper and hotter layers at the center of the disk. 37. The visible corona of the Sun is most effectively photographed A) During lunar eclipses, when the sky is darker B) In spring and fall, because of the tilt of the spin axis of the Sun C) At solar maximum periods, over a period of a few years D) During solar eclipses 38. The solar wind is A) A gentle outflow of solar material, mostly protons and electrons that is always moving outward from the Sun B) The inflow of matter onto the Sun under gravitational attraction C) The name for the electromagnetic radiation coming from the Sun D) A violent explosive expansion of specific regions of the Sun's atmosphere at certain times 39. The numbers of sunspots on the Sun vary with time in what manner? A) They increase and decrease regularly in number, at exactly 11-year intervals. B) They vary irregularly, with no periodicity. C) They increase and decrease every year as Earth revolves around the Sun. D) They vary relatively regularly, with a period of about 11 years. 40. Which of the following particles or types of radiation will provide the most direct information on the processes of nuclear fusion that are occurring in the solar core? A) Protons in the solar wind and from solar flares B) X rays from the solar corona C) Visible light from the photosphere D) Neutrinos 41. Suppose that two identical stars (having the same total light output or luminosity) are located such that star A is at a distance of 5 pc and star B is at a distance of 25 pc. How will star B appear, compared to star A? A) Star B will be 1/20 as bright as star A B) Star B will be 1/5 as bright as star A C) Star B will be 1/2.2 as bright as star A D) Star B will be 1/25 as bright as star A 42. Measurements of the brightness of a distant star through the three appropriate filters indicate that the star is brightest in U, less bright in B, and faintest in V. What conclusion can be drawn from this information, assuming no absorption of light between the star and Earth? A) The star has a very high surface temperature. B) The star has a very low surface temperature. C) This information is insufficient to allow a conclusion to be drawn about star surface temperature. D) The star has an intermediate temperature, close to that of the Sun. 43. From which feature of the light from a nearby star is the surface temperature determined most precisely? A) Relative strengths of emission lines in its spectrum B) The relative distribution of the continuum light in the spectrum C) The relative strengths of absorption lines from different atoms (for example, H, Ca) and molecules (for example, TiO) D) The Doppler shift of its spectral lines 44. The spectral class of the Sun is G2 and that of the star Enif is K2. From this information, we know with certainty that Enif is A) Hotter than the Sun B) Intrinsically fainter than the Sun C) Intrinsically brighter than the Sun D) Cooler than the Sun 45. The Hertzsprung-Russell diagram is a statistical plot of which of the following two stellar parameters? A) Luminosity and surface temperature B) Radius and mass C) Mass and surface temperature D) Luminosity and mass 46. What proportion of visible stars in the nighttime sky are multiple-star systems, such as binary stars? A) About 25 percent, or 1/4 B) Less than 1 percent C) Nearly 100 percent D) About 50 percent, or 1/2 47. If two stars of unequal mass orbit each other under mutual attraction in circular orbits, what will be the location of the center of these orbits? (See Figure 19-20) A) At a point between the stars, closest to the least massive star B) At the center of the most massive star C) At a point halfway between the star centers D) At a point between the two stars, closest to the most massive star 48. The relationship between mass and luminosity of stars on the main sequence is that A) The luminosity of stars rises to a peak at around 1 solar mass and decreases as mass increases beyond this limit. B) The greater the stellar mass, the larger the luminosity. C) Luminosity is independent of the stellar mass. D) The greater the stellar mass, the smaller the luminosity. 49. The spectrum of a very distant star shows spectral absorption lines of ionized helium, He II, and molecular absorption bands from titanium oxide, TiO. What would be your conclusion about this star? A) There must be cool, interstellar gas containing TiO between the star and Earth. B) It is obviously the spectrum of a binary system, two stars close together, a hot star and a cooler companion, unresolved as separate stars from our distance but contributing separate spectra. C) The star must have a thick, cool atmosphere overlying a hot stellar atmosphere. D) There must be a very hot atmosphere containing helium gas, overlying a much cooler stellar surface. 50. An eclipsing binary system is A) Two stars that are clearly seen as separate but associated in the sky B) Two stars whose combined light output when measured from Earth appears to vary periodically as the two stars move in front of one another C) Two stars, in which spectral lines move back and forth, indicating relative motion D) A star that is periodically eclipsed by the Moon 51. Long-exposure color photographs of the night sky often show regions that glow red, such as the Eagle Nebula. This distinctive red color is caused by A) The collective glow of many red giant stars in the region B) The emission of red and infrared light by warm dust grains C) Scattering of incoming starlight by dust grains in the nebula D) The ionization and recombination of hydrogen atoms 52. The effect of interstellar dust on starlight is A) Almost nothing, because light does not interact with dust B) To dim and redden distant stars by preferentially scattering their blue light C) To scatter the red light from stars preferentially, making them appear bluer than expected D) To make stars appear less bright than expected, by absorbing light about equally at all wavelengths 53. Protostars are A) Objects with masses less than about 0.08 solar mass, that do not have enough mass to become true stars B) Stars made almost entirely out of protons C) Very young objects, still contracting before becoming true stars D) Old stars, contracting after using up all of their available hydrogen fuel 54. At what point in its evolution will a protostar stop shrinking and stabilize into a star? A) When it has spun off enough of its matter and is spinning fast enough that centrifugal force opposes the gravitational contraction B) When the nuclear furnace ceases to work and stops attracting matter inward C) When gravitational contraction has heated up the gas to the point where radiation pressure opposes gravity for the first time D) When nuclear processes generate enough energy and internal pressure to resist gravitational contraction 55. A T Tauri star is A) A low-mass protostar near the end of its pre-main-sequence lifetime B) A young, massive O or B star C) A low-mass protostar embedded in a cocoon of dust clouds D) A high-mass protostar surrounded by a rotationally flattened disk of gas and dust Answer Key -- a3mid2 1. B 2. A 3. D 4. A 5. A 6. D 7. D 8. B 9. C 10. B 11. D 12. D 13. C 14. B 15. D 16. A 17. D 18. A 19. D 20. B 21. D 22. B 23. A 24. D 25. D 26. D 27. A 28. A 29. B 30. C 31. C 32. C 33. B 34. C 35. B 36. D 37. D 38. A 39. D 40. D 41. D 42. A 43. C 44. D 45. A 46. D 47. D 48. B 49. B 50. B 51. D 52. B 53. C 54. D 55. A