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Astronomy 12 Astronomer: KEY Final Exam Review Part I- Multiple choice: Answer each question by shading the most appropriate bubble. 01. Astronomy is the study of a. the stars and planets and their movements as well as their affects on the lives and behavior of human beings. b. the weather and of atmospheric processes. c. the structure and evolution of the earth's crust. d. everything in the universe that lies above Earth's atmosphere. 02. Which of the following terms would not be associated with astronomy? a. horoscope b. telescope c. astrolabe d. celestial sphere 03. A planet is an object which a. occurs only in our solar system. b. is too faint to see. c. orbits a star. d. does not generate its own energy from nuclear reactions 04. In astronomical terms, one brief description of a star is a. a small point of light seen only at night. b. a radiant body at least 3 million times as massive as the Earth. c. a bright object with a five-pointed shape. d. a body which shines from its own internal source of energy. 05. A galaxy is a. a large cloud of gas. b. an exploding star. c. the object from which all other objects in the universe were formed. d. a collection of a large number of stars bound by gravity. 06. A(n) _____ is the totality of all space, time, matter, and energy. a. universe b. galaxy c. planet d. star 07. Which of the following is arranged from the smallest to the largest in size? a. planet, star, universe, galaxy b. star, planet, galaxy, universe c. planet, star, galaxy, universe d. universe, galaxy, star, planet 08. What are constellations? a. galaxies of stars b. configurations of bright stars patterned by humans c. areas of the sky, each 15 x 15 degrees d. physical groupings of stars all at the same distance from Earth 09. The picture below shows Orion’s Belt. a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d Orion’s Belt Orion’s Belt is an example of a(n) a. constellation. b. asterism. c. star cluster. d. galaxy. 10. Which of the following terms is correct? a. The Big Dipper is an asterism in the constellation Ursa Major. b. Ursa Major is an asterism in the constellation of the Big Dipper. c. Both the Big Dipper and Ursa Major are constellations. d. Both the Big Dipper and Ursa Major are asterisms. 11. A band of the celestial sphere extending on either side of the ecliptic that represents the path of the different celestial bodies (i.e. Moon, Sun, planets) and contains constellations like Gemini and Aquarius is called the a. North Celestial Pole. b. South Celestial Pole. c. Celestial Equator. d. Zodiac. Astronomy 12 Test – Final Exam Review KEY Page 1 of 14 12. An imaginary sphere of infinite extent with Earth at its center on which the stars, planets, and other heavenly bodies appear to be located is known as the a. Zodiac. b. celestial sphere. c. atmosphere. d. Valhalla. 13. Which one of the following statements is true about the celestial coordinates known as "right ascension" and "declination"? a. They change from one day to the next due to the Earth's rotation. b. They are measured with respect to the observer's local zenith and horizon. c. They are fixed in space with respect to Earth's axis and the Sun's direction at the vernal equinox. d. They were used by the ancient Greeks to determine the size of the Sun. 14. FILL IN THE BLANKS: Declination is analogous to geographical ______________. Right ascension is analogous to geographical ______________. a. latitude; longitude b. longitude; latitude c. north pole; south pole d. south pole; north pole 15. The time needed for a star on the celestial sphere to make one complete rotation in the sky is referred to as a a. sidereal month. b. solar year. c. sidereal day. d. solar day. 16. The period of time between the instant when the Sun is directly overhead to the next time it is directly overhead is referred to as a a. sidereal month. b. solar year. c. sidereal day. d. solar day. 17. Relative to the stars on the celestial sphere, over the course of a year, the ecliptic is the apparent path of what celestial body? a. Moon b. Sun c. Alpha Centauri d. Earth 18. The Sun rises in the east and sets in the west because a. the Earth rotates on its axis. b. the Earth revolves around the Sun. c. the Moon revolves around the Earth. d. the Earth ‘wobbles’ on its axis. 19. The point on the ecliptic where the Sun is at its northernmost point above the celestial equator, occurring on or near June 21, is known as a. winter solstice. b. vernal equinox. c. summer solstice. d. autumnal equinox. 20. The point on the ecliptic where the Sun is at its southernmost point below the celestial equator, occurring on or near December 21, is known as a. winter solstice. b. vernal equinox. c. summer solstice. d. autumnal equinox. 21. The date on which the Sun crosses the celestial equator moving southward, occurring on or near September 22 is known as a. winter solstice. b. vernal equinox. c. summer solstice. d. autumnal equinox. 22. The date on which the Sun crosses the celestial equator moving northward, occurring on or near March 21. a. winter solstice. b. vernal equinox. c. summer solstice. d. autumnal equinox. 23. The time required for the constellations to complete once cycle around the sky and return to their starting points, as seen from a given point on Earth, is referred to as a a. synodic month. b. sidereal month. c. tropical year. d. sidereal year. 24. The time interval between one vernal equinox and the next is referred to as a a. synodic month. b. sidereal month. c. tropical year. d. sidereal year. Astronomy 12 Test – Final Exam Review KEY Page 2 of 14 a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d 25. The slow but relatively uniform motion of the earth's rotational axis that causes changes in the coordinate systems used for mapping the sky is known as a. penumbra. b. parallax. c. precession. d. phase. 26. The appearance of the sunlit face of the Moon at different points along its orbit, as seen from Earth, is referred to as a a. parallax. b. phase. c. lunar eclipse. d. solar eclipse. 27. A _____ eclipse occurs whenever the Moon passes through some portion of the Earth's shadow. a. solar b. lunar c. total d. partial 28. A _____ eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring Earth's view of the Sun. a. solar b. lunar c. total d. partial 29. The darkest part of the shadow is called the a. penumbra. b. umbra. c. baseline. d. dark zone. 30. The part of a shadow where the light source is only partially blocked is called the a. penumbra. b. umbra. c. baseline. d. light zone. 31. The difference in position of a star as seen from the Earth at different locations around the orbit of the Sun is known as a. triangulation. b. transit. c. stellar parallax. d. precession. 32. During its orbital period, as a planet moves closer to the Sun, the orbital velocity of the planet ___. (a) increases (b) decreases (c) remains the same 33. According to Newton’s law of universal gravitation, the force of attraction between any two masses is directly related to the ___. (a) distance between the masses (b) product of the two masses (c) velocity of the two masses (d) sum of the two masses 34. According to Kepler, planetary orbits are _________ in shape. a. elliptical b. circular c. spiral d. wavy 35. What are the four Terrestrial Planets? (a) Charon, Earth, Uranus, Mars (b) Mars, Venus, Mercury, Earth (c) Venus, Pluto, Mercury, Jupiter (d) Neptune, Uranus, Sol, Jupiter 35. What are the four Jovian Planets? (a) Saturn, Neptune, Jupiter, Uranus (b) Mars, Ceres, Mercury, Saturn (c) Uranus, Mercury, Mars, Neptune (d) Charon, Neptune, Uranus, Mars 36. What is another name for an interstellar gas cloud? (a) Nebula (b) Coma (c) Corona (d) Solar wind 37. What solar system object revolves around the Sun, has enough gravity to form a nearly round shape, and have no other objects of similar size in it’s orbit? (a) Planet (b) Comet (c) Meteoroid (d) Asteroid 38. Which of the following set of conditions are most likely to result in a magnetic field in a planet? (a) Liquid and electrically-conducting material in its interior and rapid rotation. (b) Closeness to Sun. (c) Iron core and slow rotation. (d) Solid surface containing iron and slow rotation. Astronomy 12 Test – Final Exam Review KEY Page 3 of 14 a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c a b c d a b c d a b c d a b c d a b c d a b c d a b c d 39. The age of the solar system has been measured by radioactive dating. Which of the following objects gives the most precise value for this age? (a) the oldest rocks from the Moon (b) the oldest rocks on the Earth (c) the oldest meteorites (d) the rocks in Mr. Jennings’ head 40. What method has been used in the successful search for planets around stars other than the Sun? (a) Hubble Space Telescope photography of faint, nearby companions of stars (b) detection of the spectral signature of methane gas near the star, since this gas is known to be a major constituent of the atmospheres of major planets (c) measurement of the "wobble" of a star, caused by the orbital motion of the planet, detected either by accurate positional measurement of the star or by spectral Doppler shifts in the stars spectrum (d) detection of the bending of light due to strong gravitational fields between Earth and the star system. 41. What happens when an object gains more matter through its gravitational pull. (a) Accumulation (b) Accretion (c) Evaporation (d) Outgassing 42. What is the outward flow of charged particles from the sun called? (a) Out gassing (b) Nova (c) Evaporation (d) Solar wind 43. What is a planet that revolves around a star, other than our sun? (a) protoplanet (b) planetesimal (c) extrasolar planet (d) exotroid 44. Using Bode’s Law for planetary orbital radii, what is the next number in the sequence of numbers: 0.4, 0.7, 1.0, 1.6, 2.8, ____ (a) 10.0 (b) 5.2 (c) 4.8 (d) 4.4 45. Light has a particle nature, and these particles are called photons. Which region of the electromagnetic spectrum has the highest energy photons? (a) gamma ray (b) ultraviolet (c) visible (d) infrared 46. A source of light moves toward you. According to the Doppler effect (a) the frequency of the light will increase. (b) the frequency of the light will decrease. (c) the wavelength of the light will increase. (d) the velocity of the light will increase. 47. The spectral classification of a star is closely related to the star’s (a) brightness. (b) luminosity. (c) surface temperature. (d) distance. 48. How does the H-R diagram help astronomers identify stars? (a) It plots a star’s mass and core temperature, which allows astronomers determine the colour and region of where star is formed. (b) It plots a star’s luminosity and spectrum, which allows astronomers determine the size of the star. (c) It plots a star’s luminosity and surface temperature, which allows astronomers determine the type of star, size of star, and the star’s stage of evolution. (d) It plots a star’s size and surface temperature, which allows astronomers determine its region of origin. 49. What is the Main Sequence? (a) The evolutionary path, as seen on the H-R diagram, that a star follows throughout its life. (b) The region on the H-R diagram where, once they are formed. new stars rest for most of their lives. (c) The sequence of events a star follows from its formation to supernova. (d) The region on the H-R diagram where protostars first appear. 50. Define hydrogen burning. (a) The formation of a hydrogen gas cloud, also known as a nebula. (b) The chemical combustion of hydrogen. (c) the separation of the hydrogen envelope to form a planetary nebula. (d) The formation of helium by fusing hydrogen together. 51. When a star’s gravitational force pulling inwards and its internal pressure pushing outward are balanced, it is considered to be in what? (a) Hydrostatic equilibrium (b) Supernova (c) Structural Balance (d) Proton-proton fusion 52. What is a helium flash? (a) The rapid fusion of helium in a red giant’s core. (b) An explosion that creates a planetary nebula. (c) A type of solar flares that occurs on the surface of sun-type stars. (d) A flash of white light that occurs when a star collapses into a white dwarf. 53. What is a planetary nebula? (a) The destroyed remains of a planetary solar system when a sun-type star expands to a red giant. (b) The ejected envelope of a red giant that was formed from a sun-type star. (c) The disk of material around a protostar that will eventually form planetary system. (d) The initial massive gas cloud that stars and planets are formed from. Astronomy 12 Test – Final Exam Review KEY Page 4 of 14 a b c d a b c d either C or D a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d a b c d 54. A white dwarf found in a binary system suddenly brightens, settles back down in a few months, and has the possibility to repeat. What is this called? (a) Red Giant (b) Carbon-detonation supernova (Type One) (c) Planetary nebula (d) Core collapsing supernova (Type Two) 55. High-mass protostars evolve into main-sequence stars (a) more quickly than low-mass protostars because their stronger gravity speeds up their collapse. (b) more quickly than low-mass protostars because their higher core temperature speeds up their collapse. (c) more slowly than low-mass protostars because their stronger gravity slows their collapse. (d)s more slowly than low-mass protostars because their higher core temperature slows their collapse. 56. In which of the following types of galaxies would you be least likely to find a newly-formed star? a) Elliptical b) Spiral c) Irregular Use the diagram below to answer the next 3 questions: 57. Region #1 is referred to as the galactic _____. a) halo b) disk c) bulge d) cluster 58. Region #2 is referred to as the galactic _____. a) halo b) disk c) bulge d) cluster 59. Region #3 is referred to as the galactic _____. a) halo b) disk c) bulge d) cluster 60. What does Hubble’s law tell us about how galaxies are moving? a) All galaxies are moving away from us at the same velocity. b) Galaxies close to us are receding from us slowly, and galaxies farther from us are receding more rapidly. c) Galaxies close to us are receding from us rapidly, and galaxies farther from us are receding more slowly. d) Galaxies have random distribution of velocities—there is no pattern. 61. The cosmic microwave background radiation is a) all of the radiation currently existing in the universe produced by all possible sources. b) all of the radiation emitted by stars since the first stars were born. c) leftover radiation from the original Big Bang that has been tremendously redshifted by the expansion of the universe. d) radio emission from various radioactive galaxies. Astronomy 12 Test – Final Exam Review KEY Page 5 of 14 a b c d a b c d a b c a b c d a b c d a b c d a b c d a b c d Part II- Short Answer: Answer each question on the test paper in the space provided. 49. Label the various parts of the celestial sphere below: A Celestial Equator B Ecliptic C North Celestial Pole D South Celestial Pole E Earth 50. Explain how right ascension and declination are used to locate objects in the sky. -start at the vernal equinox -move eastward through 0 to 24 hours (analogous to moving through different geographical longitude lines) -move north (+) or south (-) through 0 to 90 degrees to the object’s location (analogous to moving through different geographical latitude lines) 51. The solar day is 3.9 minutes longer than the sidereal day. Why is this so? -solar day takes into account the Earth’s revolution around the Sun during its rotation on its axis and is therefore longer. 52. Why does Earth experience seasons? Be sure to mention Earth’s rotational axis and the Sun’s energy in your answer. Astronomy 12 Test – Final Exam Review KEY Page 6 of 14 As seen in the diagram above, during the winter season, the Northern Hemisphere is tilted away from the Sun and receives less direct sunlight. This means that the atmospheric temperature does not rise as much as in summer. During the summer season, the Northern Hemisphere is tilted towards the Sun and receives more direct sunlight. This means that the atmospheric temperature rises more than in the winter. 53. The sidereal year is about 20 minutes longer than the tropical year. a. Why is this so? The sidereal year is the time for the Earth to revolve around the Sun relative to the stars, while the tropical year is the time for the Earth to revolve around the Sun relative to the vernal equinox. These two years are slightly different because precession causes the vernal equinox to move relative to the stars. b. If modern calendars were based on the sidereal year, what would be the effect on timekeeping? The calendar is based on the tropical year so that the first day of spring occurs approximately on the same date each year. If the calendar was based on the sidereal year, eventually important dates like Easter and Christmas would be at different dates throughout the year. 54. Label the phases of the Moon. Indicate phase name below its image. New Moon Waxing Crescent 1st Quarter Waxing Gibbous Full Moon Waning Gibbous 3rd Quarter Waning Crescent 55. One sidereal month is 27.3 days. One synodic month is 29.5 days. Explain this difference. The sidereal month is the time that the Moon takes to go around the Earth once relative to the stars. The synodic month is the time that the Moon takes to go around the Earth relative to the Sun. The synodic month is longer by about 2.3 days. During the sidereal month the Sun appears to move about 27 o due to the Earth’s orbital motion. It takes the extra 2.3 days for the Moon to catch up to the Sun. 56. Draw a diagram that would illustrate a lunar eclipse. Astronomy 12 Test – Final Exam Review KEY Page 7 of 14 57. Draw a diagram that would illustrate a solar eclipse. Indicate the regions on Earth’s surface where total and partial eclipses would be seen. 58. Explain how astronomers use triangulation to find stellar distances. You can use the astronomical unit calculation activity as an example. This is stellar parallax. Parallax involves measuring the distances to nearby stars, whose display an apparent shift in position against background stars observed as Earth moves along its orbit. 59. How does the Earth’s axial tilt of 23.5o determine why is it hotter in the summer and colder in the winter in the Northern Hemisphere? {see answer to #52} 60. Recall the night-time observation assignment that required you to locate the approximate location of the North Celestial Pole in the sky. If you were a student in Astronomy 12 in the year 15 000 C.E., how would this task be different? The task would be different due to precession, which shifts the NCP from Polaris to Vega in 12 000 years (i.e. 2012 C.E. + 12 000 years = 15 000 C.E.). 61. Tides are periodic rises and falls of large bodies of water. Tides are caused by the gravitational interaction between the Earth and the Moon; the Sun also exerts a gravitational attraction on the Earth but to a lesser degree. The gravitational attraction causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side). Since the earth is rotating while this is happening, two tides occur each day. Spring tides are especially strong tides (they do not have anything to do with the season Spring). Neap tides are especially weak tides. Given all these points, draw diagrams of that illustrate the difference between spring and neap tides. Astronomy 12 Test – Final Exam Review KEY Page 8 of 14 62. Construct a Venn Diagram comparing and contrasting the geocentric and heliocentric models of the universe. Geocentric Universe -Earth-centered with Sun, Moon, planets revolving around Earth -required deferent for main orbital path and epicycle to account for retrograde motion -could not explain stellar parallax Heliocentric Universe -both described geometry of Solar System -both attempted to explain retrograde motion -Sun-centered with Earth, Moon, planets revolving around Sun -no epicycle required (i.e. retrograde motion explained by planets revolving at various speeds) -could explain stellar parallax 63. Draw a label a diagram that illustrates the geocentric model of the solar system. Be sure to include the following parts: deferent, epicycle, planet, Earth, Sun. 64. Define perihelion and aphelion. Perihelion is the point on the orbital path of a planet closest to the Sun; aphelion is the point on the orbital path of a planet farthest from the Sun. 65. State Kepler’s 3 Laws of Planetary Motion. 1st: the orbit of a planet about the Sun is an ellipse with the Sun at one focus 2nd: a line joining a planet and Sun sweeps out equal areas in equal time intervals (i.e. a planet travels fastest at the perihelion and slowest at aphelion) 3rd: the period of a planet’s orbit squared (in years) is equal to the orbital radius of the planet cubed (in AU) (i.e. P2 = a3) 66. State Newton’s Law of Universal Gravitation. The gravitational attractive force between two objects (i.e. a planet and the Sun) is directly related to the product of the mass of the two objects and inversely related to the square of the distance between them. 67. State Newton’s three laws of motion. First law: The velocity of a body remains constant unless the body is acted upon by an external force. Second law: The acceleration a of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = m x a. Third law: For every action, there is a reaction force, equal in magnitude (i.e. size) but opposite in direction 68. The orbital distance from Saturn to the Sun is approximately 10.0 A.U. Using Kepler’s 3 rd Law of Planetary Motion (P2 = a3), what is the period of Saturn (or the time it takes Saturn to revolve around the Sun)? P2 = a3 P = √(10.0 AU)2 = 31.6 years Astronomy 12 Test – Final Exam Review KEY Page 9 of 14 69. It takes Mars 688 days to revolve around the Sun. What is its orbital distance from the Sun? Convert 688 days to years….688/365 = 1.88 years P2 = a3 a = cube root [(1.88 years)2] = 1.52 AU 70. State Newton’s revisions to Kepler’s Laws of Planetary Motion. 1st law: Newton agreed with Kepler but said that orbits could be elliptical if bound and the planet would continue to orbit regularly. Orbits could be parabolic or hyperbolic if unbound (i.e. planet passes Sun once and leaves Solar System) 2nd law: Newton said that the change in velocity or acceleration of a planet around the Sun is due to gravity 3rd law: Newton agreed that P2/a3 ratio was true for all planets in Solar System but was able to use gravity to determine the mass of Sun 71. State Bode’s Law. Compare its usefulness and accuracy to Kepler’s 3rd Law of Planetary Motion. Bode’s law is a pattern of numbers that predict the orbital distances (in AU) from the Sun to all the planets with reasonable accuracy: 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0, 19.6, 19.6, 38.8 It is useful for approximate distances but only useful for planets and not other Solar System objects. Kepler’s 3 rd law can be used to find orbital distances of any Solar System object. 72. Use Bode’s Law to predict the orbital radius of the Asteroid Belt. At 2.8 AU in the Bode’s law pattern, a planet was predicted to exist. After careful searching, astronomers determined that at this distance, the Asteroid Belt resides and not a planet. 73. Using Newton’s law of gravitation, if the distance between a planet and the Sun increases by a factor of 4, how does the force of gravity between the planet and Sun change? The force of gravity would decrease by a factor of 16 (i.e. 42 = 16). 74. List Newton’s laws of motion and an example for each. {see answer to #67; examples will vary} 75. List the major types of structures in the solar system, from the largest to the smallest mass. Sun, planets, moons, asteroids, comets 76. Why is Pluto no longer considered a planet? It has a highly eccentric orbit (eccentricity = 0.25). It is a very rocky object. Numerous trans-Neptunian objects the size of Pluto have been discovered. 77. Explain how the planets in our solar system were formed. 6 Steps to Form a Solar System THE NEBULAR HYPOTHESIS 1. Solar Nebula Forms A huge cloud of cold gas and dust. Many times larger than our present solar system. Probably spinning very slowly. 2. Formation of the Protosun Under the influence of gravity, the solar nebula condensed into a dense central region (the protosun) and a diffuse outer region (the protoplanetary disk). Began to spin faster, flattened out, and central region heated up. 3. Rings and Planetesimals Instabilities in the rotating disk caused regions within it to condense into rings under the influence of gravity. Gradually, planetismals formed in these rings. 4. Terrestrial or Rocky Planets The planetismals attracted each other by gravity and collided to build planets. Closest to the protosun, only rocky material and metals could withstand the heat, and so the planets in this region are made mainly of these materials. Astronomy 12 Test – Final Exam Review KEY Page 10 of 14 5. Jovian or Gas Giants In the outer part of the disk, the bodies formed from planetesimals made of rock and ice. They became big enough to attract large amounts of gas around them. Soon after these gas planets formed the protosun became a full-fledged star. 6. Remaining Debris Radiation from the Sun blew away most of the remaining gas and other material in the planetary solar system. Some of the leftover planetismals in the outer part of the disk formed the Kuiper Belt and Oort cloud of comets. 78. Describe the difference between how terrestrial and jovian planets were formed. Use diagrams, if needed. For jovian planets, initially core formed by accretion of solid materials and then, gas accreted onto solid core to form gas giant (i.e. core accretion model). Alternatively, gases rapidly accrete and condense to form Jovian planets without a solid core due to denser areas in the protoplanetary disk (i.e. disk instability model). 79. A star is has a parallax of 0.02 arcseconds. How far away is this star? SHOW ALL WORK & CALCULATIONS Use d = 1/p d = 1/(0.02’’) = 50 parsecs 80. Describe the methods by which extrasolar planets are detected. Transit Method If a planet crosses (or transits) in front of its parent star's disk, then the observed visual brightness of the star drops a small amount. The amount the star dims depends on the relative sizes of the star and the planet. Astrometry This method consists of precisely measuring a star's position in the sky and observing how that position changes over time. If the star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit. If the star is large enough, a ‘wobble’ will be detected. Doppler Shift (Radial Velocity) A star with a planet will move in its own small orbit in response to the planet's gravity. The goal now is to measure variations in the speed with which the star moves toward or away from Earth. In other words, the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star's spectral lines (think ROYGBIV) due to the Doppler effect. Pulsar Timing A pulsar is a neutron star: the small, ultra-dense remnant of a star that has exploded as a supernova. Pulsars emit radio waves extremely regularly as they rotate. Because the rotation of a pulsar is so regular, slight changes in the timing of its observed radio pulses can be used to track the pulsar's motion. Like an ordinary star, a pulsar will move in its own small orbit if it Astronomy 12 Test – Final Exam Review KEY Page 11 of 14 has a planet. Calculations based on pulse-timing observations can then reveal the geometry of that orbit Gravitational Microlensing The gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned. If the foreground lensing star has a planet, then that planet's own gravitational field can make a detectable contribution to the lensing effect. Direct Imaging Planets are extremely faint light sources compared to stars and what little light comes from them tends to be lost in the glare from their parent star. It is very difficult to detect them directly. In certain cases, however, current telescopes may be capable of directly imaging planets. 81. A star has a surface temperature of 10 000 K. What is the peak wavelength (in meters) of light emitted from the surface? SHOW ALL WORK & CALCULATIONS Use Wein’s Law max = (0.0029 Km)/T = (0.0029)/(10000 K) = 0.00000029 m = 290 nm (blue light) 82. Describe at least three properties of a star that an astronomer can deduce from its spectrum. (1) chemical composition, from the presence of the characteristic spectral lines of certain elements; (2) temperature, from spectral type; (3) star’s speed toward or away from us, from Doppler shift of the lines; (4) density, axial rotation, and surface magnetic fields, from line shape and width. 83. If a red star and a blue star have the same radius and brightness, which one is farther from Earth? Explain why. Because the stars have the same radius, the lower-temperature red star (using Wein’s law) must be nearer (using Stefan-Boltzmann law) in order to have the same apparent brightness as the higher-temperature blue star. 84. If a red star and a blue star have both appear equally bright and both are the same distance from Earth, which one has the larger radius? Explain why. Because the stars are the same brightness and distance from Earth, the lower-temperature star (using Wein’s law) red star must be larger (using Stefan-Boltzmann law) in order to have the same brightness as the highertemperature blue star. 85. Complete tree diagram below: describe the two types of supernovas. Supernova Type I – Carbon Detonation -lack H lines in spectra -can be formed from WD in binary system or supergiants with H/He removed -found everywhere in Galaxy -produced from old, low-mass stars -fixed maximum brightness Type II – Core Collapsing -have H lines in spectra -formed from young, massive stars -observed in arms of spiral galaxies -end result: NS or BH -stay brighter longer, with variable maximum brightness brightness decreases rapidly Astronomy 12 Test – Final Exam Review KEY Page 12 of 14 77. Complete table below: For each STAGE, write the letter of its STAGE DESCRIPTION in the corresponding blank. See #7 as an example. H-R Diagram Stage (7 to 14) Stage Description 7. ___F___ A. B. C. D. 8. ___I___ 9. ___C___ 10. ___D___ 11. ___L___ 12. ___B___ E. F. G. H. I. 13. ___M___ 14. ___A___ J. K. L. M. Black Dwarf Planetary Nebula Helium Flash Carbon core expands and star returns to a balance state. Supernova New Star Oxygen fusion Carbon burning Forms a helium core as it leaves the main sequence Protostar Fragmentation Carbon core contracts and star climbs Giant branch again. White dwarf 78. Explain the general formation of a sun-type star (i.e. Steps 1-6). Stage 1: Fragmentation of Nebula with sufficient mass, nebula fragments repeatedly under gravity Stage 2: Fragmentation Stops lower-mass fragments form until internal gas pressure greater than gravity and fragmentation stops; thin fragment with hot center Stage 3: Formation of a Protostar protostar and protoplanetary disk form; heat and light from gravitational energy at the core produce YSO (no fusion) Stage 4: Can be Seen on H-R diagram no fusion but gravitational collapse produces sufficient surface temperature and luminosity to be measured on H-R diagram Stage 5: Violent Surface Activity due to increasing core pressure from gravity, core traps heat that is released from time to time, causing violent surface activity Stage 6: Helium Core is Formed core temperature sufficient to produce proton-proton fusion and helium deposited in core 79. Complete the Venn diagram to the right in order to compare the history of high mass stars with low mass stars (Hint: think the formation, evolution and death of the different stars). 80. A star has a mass of 8.5 solar masses. Predict what will happen to this star when it leaves the Main Sequence on the HR Diagram. When this star leaves Main Sequence, because of its high mass, it will become a blue supergiant, undergoing heavy element burning. This produces iron in the stellar core. Once all fusion processes cease, the star core contracts rapidly producing a supernova explosion. The core remnant from this event is a neutron star, a densely-packed core of neutrons (produced from compacted protons and electrons), with a strong magnetic field. Astronomy 12 Test – Final Exam Review KEY Page 13 of 14 (note: if the original star were about 10 solar masses or greater, the supernova remnant would have been a black hole). 81. Using the Hubble Classification of Galaxies below, classify the four galaxies. Sb Irr E5 (or S0) SBb 82. Explain why Hubble’s Classification System cannot be used as an evolutionary path of galaxies. If Hubble’s classification system could be used as an evolutionary path of galaxies, then elliptical galaxies would eventually form into spiral galaxies. This means that spiral galaxies should only contain very old stars Since spiral galaxies contain both young and old stars, they cannot have formed from elliptical galaxies 83. Describe the dark-matter problem. How is dark matter detected in the Universe? The dark matter problem is the mystery that most of the matter in the Universe seems not to emit radiation of any kind and is detectable by gravity alone. Dark matter is indirectly detected by its gravitational effects on ‘regular matter’, including galaxy rotation and gravitational lensing. 84. How is the formation of spiral and elliptical galaxies related to the initial rate of star formation in the protogalactic nebulae from which they were formed? The initial rate of star formation in elliptical galaxies is thought to be much greater than that of spiral galaxies The increased amount of time for initial star formation allowed spiral galaxies to form as they did 85. The Universe is considered to be both homogenous and isotropic. Explain the difference between these terms. On large scales, the Universe is homogenous, which means that there are similar properties in every region. “Isotropic” means that the Universe is the same in all directions (i.e. there is no preferred location in the Universe in which to measure the Universe). 86. Using Hubble’s Law (v = H0 x d), find the velocity of a galaxy that is 100 Mpc from the Milky Way Galaxy. (Note: H0 = 74.3 km/s/Mpc) v = H0 x d = (74.3 km/s/Mpc)(100 Mpc) = 7430 km/s therefore, galaxies that are 100 Mpc away in any direction are moving away from the Milky Way at 7430 km/s 87. Describe four pieces of evidence that suggest that the Big Bang is the best model for describing the formation of the universe. Redshift of light from distant galaxies Hubble law of expansion The presence and temperature of cosmic microwave background radiation (CMBR) Evolved structures, e.g. galactic clusters, galaxies, stars Abundance of lighter elements, e.g. H and He, in the Universe (1st elements to be produced after initial Big Bang) 88. Contrast three possible fates of the Universe in the future. Relate each fate to the Universe’s critical density. Which fate do cosmologists feel is most likely to occur? Open: Universe expands at an accelerating rate; density is less than critical density (Big Rip) Closed: Universe’s expansion slows and halts and collapses under gravity; density is greater than critical density (Big Crunch) Flat: Universe expands at a constant rate of acceleration, without ripping apart or crunching; density is equal to critical density Cosmologists feel that the Universe is flat and will expand forever. They think this due to data collected from COBE and WMAP missions. Astronomy 12 Test – Final Exam Review KEY Page 14 of 14