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 clicker Spring 2018 ASTR 1200-001 General Astronomy: Stars & Galaxies: Clicker Questions

    Wed 2018 Jan 17 (not graded):

  1. I know you all want an A in this class, and will work hard to make it so, but realistically what grade do you think you will get?
    A. A;
    B. B;
    C. C;
    D. D;
    E. F.

    Fri 2018 Jan 19 (not graded):

  2. On the scale of the Model Solar System that starts with the Sun just outside the Fiske Planetarium and extends to Pluto near the Engineering building, about how far away is the nearest star?
    A. Folsom Stadium (1 km);
    B. 3500 19th St, North Boulder (3 km);
    C. Denver (30 km);
    D. Aspen (300 km);
    E. New York (3,000 km).

  3. If you made a model of our Milky Way galaxy that was about as big as the Model Solar System, about how far away would be the nearest star on that scale?
    A. Pin (0.3 mm);
    B. Straw (3 mm);
    C. Finger (3 cm);
    D. Person (3 m);
    E. Room (30 m).

  4. Roughly how many galaxies are in this Hubble Ultra Deep Field image?
    A. 102;  
    B. 103;
    C. 104;
    D. 105;
    E. 106.
    Hubble Ultra Deep Field

    Wed 2018 Jan 24:

  5. Which is nearest to us on Earth?
    Sun
    A.
    Jupiter
    B.
    Star-forming region in the sword of Orion
    C.
    Whirlpool galaxy
    D.
    Cosmic Microwave Background
    E.
  6. Which is farthest from us on Earth?

  7. Which of the following is not a form of light:
    A. Radio waves;
    B. Microwaves;
    C. Electrons;
    D. X-rays;
    E. Gamma-rays?

    Fri 2018 Jan 26:

  8. The higher the photon energy:
    A. the longer its wavelength;
    B. the shorter its wavelength;
    C. energy is independent of wavelength.

  9. In what ways is an electron orbiting the nucleus of an atom like a planet orbiting the Sun?
    A. Both are held in orbit by a force.
    B. The smallest orbits are the most tightly held.
    C. If you give an electron or a planet more energy, it will move to a bigger orbit.
    D. If you give an electron or a planet enough energy, it can break free.
    E. All of the above.

  10. In what ways is an electron orbiting the nucleus of an atom different from a planet orbiting the Sun?
    A. The central force is the electromagnetic force, not gravity.
    B. Not all orbits are allowed (they are quantized).
    C. An electron can jump or make a transition from one orbital to another.
    D. All of the above.

  11. If you looked at an extremely hot star (surface temperature of say 30,000 Kelvin) what color would it appear to be? (You are wearing neutral filter dark glasses so the light does not blind you).
    A. Reddish;
    B. Bluish;
    C. Violet;
    D. White;
    E. Black — the star emits its light in ultraviolet and x-rays, not in visible light.

    Mon 2018 Jan 29:

  12. Why don't you glow in the dark?
    A. People do not emit any light;
    B. People only emit light that is invisible to our eyes;
    C. People are too small to emit enough light for us to see;
    D. People do not contain enough radioactive material.

  13. An Astronomical Unit (au) (the distance between the Earth and the Sun) was first measured reliably by Cassini in 1672:
    A. From a measurement of the distance to the Moon;
    B. Using radar bouncing off the surface of the Sun;
    C. Using a measurement of the parallax of Mars;
    D. From the orbital periods of the Galilean moons of Jupiter;
    E. From the temperature and power output (luminosity) of the Sun.

  14. The distance between the Earth and Sun is one of the ingredients needed to measure directly the Sun's mass. Which is the other ingredient?
    A. The Sun's surface temperature;
    B. The Sun's luminosity;
    C. The Sun's rotation period;
    D. The Earth's rotation period;
    E. The Earth's orbital period.

  15. The core of the Sun is undergoing the same process of nuclear fusion that occurs when a hydrogen bomb explodes. Why does the Sun not explode?
    A. Because it is an ionized plasma of electrons and nuclei;
    B. If its temperature increases, the core expands, causing its temperature to decrease;
    C. Neutrinos carry energy away from the core, cooling it;
    D. It is exploding, but gravity contains the explosion;
    E. The core is constantly undergoing mini-explosions, which reveal themselves through seismic oscillations of the Sun surface.

    Wed 2018 Jan 31:

  16. What profound new idea did Arthur Eddington have that revolutionized our concept of the Sun?
    A. That the Sun is the center of the Solar System;
    B. That mass and energy are equivalent;
    C. That the interior of the Sun is an ionized plasma, which is compressible like a gas;
    D. That the Sun is made of hydrogen;
    E. That the Sun is a star.

  17. How did Eddington estimate the temperature at the center of the Sun?
    A. From the wavelength of the peak of the visible light spectrum of the Sun;
    B. From the equivalence of energy and mass (\(E = m c^2\));
    C. By estimating the temperature needed to ionize hydrogen;
    D. By estimating the temperature needed to start fusing hydrogen;
    E. By equating the particle velocity to gravitational escape velocity.

    Dopplergram of the Sun

  18. This dopplergram of the Sun seems to be brighter on one side than the other. Why?
    A. The Sun is intrinsically hotter on one side than the other;
    B. The Sun is moving sideways;
    C. The Sun is rotating about its axis;
    D. The Earth is rotating about the Sun;
    E. The Earth is rotating about its axis.

  19. Solar granulation, coronal loops, coronal heating, and coronal mass ejections are all powered by:
    A. Nuclear fission (radioactivity);
    B. Nuclear fusion;
    C. The conversion of mass to energy;
    D. Gravity;
    E. Convection.

    Mon 2018 Feb 5:

    levels of H atom, showing Ha, Hb, Hg absorption transitions

  20. When should H\(\alpha\), H\(\beta\), H\(\gamma\), ... absorption in a star be strong?
    A. When the \(n = 1\) (ground) level is most populated;
    B. When the \(n = 2\) level is most populated;
    C. When the \(n = 3, 4, 5, ...\) levels are most populated;
    D. When H is mostly ionized.

  21. When is the \(n = 2\) level of H most populated?
    A. Low temperature;
    B. Intermediate temperature;
    C. High temperature.

    How light emitted by a star spreads out with distance (Fig 16.2 of Cosmic Perspective)

  22. The figure illustrates how light emitted by a star spreads out with distance d from the star. It follows from the figure that the apparent brightness of a star varies with distance d as:
    A. \(1 / d^2\) because the light spreads in proportion to area;
    B. \(1 / d\) because the light spreads out in proportion to distance;
    C. it does not vary with distance, because the total light is the same even if it spreads out;
    D. \(d\) because the light spreads out in proportion to distance;
    E. \(d^2\) because the light spreads out in proportion to area.

  23. Why can parallax be used to measure the distances only of nearby stars?
    A. The parallaxes of distant stars are too small to measure;
    B. Distant stars are too faint to measure;
    C. The light travel time to distant stars is too long;
    D. Distant stars are so numerous that they become confused with other stars;
    E. Distances of distant stars increase rapidly as the Universe expands.

    Wed 2018 Feb 7:

  24. Discussion question (no right answer):
    A. Leave Mars alone.
    B. Send robots to Mars to search for life.
    C. Send people to visit Mars.
    D. Send people to colonize Mars.
    E. Colonize Mars and Save Humanity.

  25. Annie Jump Cannon rearranged the spectral types of stars into the sequence OBAFGKM. Cecilia Payne-Gaposchkin subsequently showed that this sequence represented a sequence of:
    A. Mass;
    B. Radius;
    C. Surface Temperature;
    D. Age;
    E. Composition.

  26. The bright blue stars in the Pleiades are located in the HR diagram:
    A. Top left;
    B. Top right;
    C. Center;
    D. Bottom left;
    E. Bottom right.

  27. The radius of a star at a given position in the HR diagram can be deduced from:
    A. Its parallax;
    B. Its spectral type;
    C. Its luminosity;
    D. The Stefan-Boltzmann law \(L = 4 \pi R^2 \sigma T^4\);
    E. The position of a star in the HR diagram is not enough to deduce its radius.

    Fri 2018 Feb 9:

  28. Flying above the blurring effect of the atmosphere, the ESA Gaia satellite is obtaining parallaxes down to about 10–5 arcsec. Gaia will be able to measure distances of stars out to about:
    A. 10–5 parsecs;
    B. 1/300 of a parsec;
    C. 300 parsecs;
    D. 105 parsecs;
    E. 1010 parsecs.

  29. Some star clusters are too far away for their distances to measured by parallax. The distance to such a star cluster can be measured from:
    A. The apparent brightness of the main sequence on its HR diagram;
    B. The average distance between the stars;
    C. The average redshift (Doppler shift) of the stars;
    D. The average temperature of the stars;
    E. It's position in the Milky Way.

  30. In HW 2 you found that at its current rate of energy generation, about 4 million tons per second, the Sun fusing H to He (rest mass conversion efficiency 0.007) could last for 1011 years, whereas a more detailed calculation shows that the Sun's main sequence lifetime is only 1010 years. Why the discrepancy?
    A. We made a dumb error in HW 2;
    B. After burning 10% of its core to He, the Sun starts burning He, beginning its journey to red gianthood;
    C. The Sun's composition is only 10% H, the remainder being heavy elements;
    D. 90% of the energy goes into plasma pressure;
    E. 90% of the energy escapes in neutrinos.

  31. The main sequence lifetime of the Sun burning hydrogen is 1010 years. What is the main sequence lifetime of star of 10 solar masses, which has luminosity 104 times the luminosity of the Sun?
    A. 107 years;
    B. 108 years;
    C. 109 years;
    D. 1011 years;
    E. 1013 years.

    Wed 2018 Feb 14:

  32. Which of the following is false? The stars in a star cluster have almost the same:
    A. Position on the sky;
    B. Distance;
    C. Age;
    D. Initial composition;
    E. Mass.

  33. At its core, the Sun is fusing hydrogen to helium, something that can only happen at high temperature, about \(10^7 \, \textrm{K}\). The source of energy that allowed the Sun to heat up enough to begin fusing nuclei was:
    A. The Big Bang;
    B. Electric currents generated by magnetic fields;
    C. Chemical energy;
    D. Nuclear fission;
    E. Gravitational contraction.

    Orion nebula (HST) Orion nebula (Ryan Steinberg and Family/Adam Block/NOAO/AURA/NSF)

  34. We know that the Orion nebula is a star-forming region (a region containing stars that are much younger than the 14 billion year age of the Universe) because:
    A. It contains hot, luminous main sequence stars;
    B. It contains glowing, ionized Hydrogen gas;
    C. It is adjacent to a molecular cloud;
    D. It is in a spiral arm;
    E. It contains lots of stars close together.

  35. The Sun will end its life as:
    A. A red giant;
    B. A supergiant;
    C. A white dwarf;
    D. A neutron star;
    E. A black hole.

    Mon 2018 Feb 19:

  36. What is a planetary nebula?
    A. A system of planets forming around a star;
    B. A region of gas and dust where stars are forming;
    C. A red giant blows off its envelope in a powerful wind, leaving behind its core, a future white dwarf;
    D. A globular cluster;
    E. A galaxy.

  37. How do astronomers conclude that certain stars in a star cluster are white dwarfs?
    A. From their spectral types and luminosities;
    B. From their ages;
    C. From their masses;
    D. From their compositions;
    E. From their parallaxes.

  38. Sirius A is a main sequence star of mass 2 solar masses, while Sirius B is a white dwarf of mass 1 solar mass. Which star was more massive when the binary system formed?
    A. Sirius A;
    B. Sirius B.

  39. You fire a rocket from Earth. Which rocket wins the orbital race (which rocket returns first to the starting point)?
    A. The rocket that stays on Earth;
    B. The rocket that fires forwards;
    C. The rocket that fires outwards;
    D. The rocket that fires backwards;
    E. The rocket that fires inwards.

    Rocket fired from Earth              Resulting orbits

  40. Which electrons contribute the greatest degeneracy pressure?
    A. Electrons with the shortest wavelengths;
    B. Electrons with the longest wavelengths;
    C. All electrons contribute equally to the pressure.

    Wed 2018 Feb 21:

  41. What kind of pressure holds up a white dwarf star against its own gravity?
    A. The pressure of a liquid or solid of atoms.
    B. The pressure of a gas of atoms.
    C. The pressure of a hot gas of nuclei and electrons (a plasma).
    D. Electron degeneracy pressure.
    E. Neutron degeneracy pressure.

  42. Suppose you confine an electron in a box (which effectively is what a white dwarf does to the electrons in its interior). If you remove as much energy as possible from the electron, then the electron will:
    A. Come to a halt, with zero energy;
    B. Keep moving, because the box keeps the wavelength to a certain minimum size, forcing the electron to have some energy.

  43. Astronomers ruled out intelligent life as an explanation for pulsars because pulsars were found to emit over a wide range of radio frequencies. The argument is that:
    A. Intelligent life would probably emit optical signals, not radio signals;
    B. Intelligent life would probably vary the frequency, so that it would encode an intelligible signal;
    C. Intelligent life would probably emit signals at a single narrow frequency, to make the most efficient use of energy.

    Fri 2018 Feb 23:

  44. What kind of supernova is this?
    A. Core-collapse;
    B. Thermonuclear.

    Drop a superball on top of a basketball

  45. You drop a basketball and a superball together, the superball on top of the basketball. How high does the superball bounce?
    A. Lower than the height from which it was dropped;
    B. To roughly the same height as from which it was dropped;
    C. Higher than the height from which it was dropped?

  46. Repeat the experiment with a smaller superball. Does the smaller superball bounce lower or higher than the larger superball?
    A. Lower;
    B. Roughly the same;
    C. Higher.

  47. Both types of supernova (core collapse and thermonuclear) are initiated by the collapse of an electron-degenerate core that reaches the Chandrasekhar limit of 1.4 solar masses. What causes the difference in outcomes?
    A. The composition of the core, iron versus carbon-oxygen;
    B. A difference in the mass of the envelope surrounding the core;
    C. The gravity of the core;
    D. Magnetic fields;
    E. Chance.

    Mon 2018 Feb 26:

  48. LIGO measures the distance between freely-hanging mirrors 4 kilometers apart to a precision of:
    A. 10–3 times the size of a proton nucleus;
    B. The size of a proton nucleus;
    C. The size of an atom;
    D. The wavelength of visible light;
    E. The wavelength of a gravitational wave.

  49. What was the approximate wavelength of the gravitational waves detected?
    A. About 10–3 times the size of a proton nucleus;
    B. About the size of a proton nucleus;
    C. About the size of an atom;
    D. About the wavelength of visible light;
    E. About the size of the merging black hole system (few 1000 km).

  50. Why does the detection of a burst of gamma rays 2 seconds after the gravitational wave signal in GW170817 imply that the speed of gravitational waves is the speed of light?
    A. Because gamma-rays are a kind of gravitational wave;
    B. Because general relativity predicts that gravitational waves move at the speed of light;
    C. Because the signal travelled the same distance, 130 million lightyears, in the same time;
    D. Because extremely energetic particles must move at the speed of light;
    E. Actually, the fact that the gamma-ray signal was delayed by 2 seconds implies that gravity moves slightly faster than light.

  51. Which merger produces an electromagnetic signal that astronomers can detect?
    A. The merger of two black holes;
    B. The merger of two neutron stars;
    C. Both types of merger.

  52. Discussion question: If a gravitional wave is a wave of spacetime that changes distances between things, including the lengths of rulers that measure distances, how can gravitational waves be measured?

    Wed 2018 Mar 7:

  53. If you want to find a black hole on the sky, the best kind of light to look in is:
    A. Radio;
    B. Infrared;
    C. Visible;
    D. Ultraviolet;
    E. X-ray.

  54. According to Special Relativity, if a car moves at almost the speed of light relative to a person, and the car emits a beam of light in the direction it is moving, then the person will measure the speed of the light emitted by the car to be:
    A. Almost twice the speed of light;
    B. Exactly the speed of light;
    C. Less than the speed of light.

  55. From Einstein's assertion that the speed of light is the same for all observers, it follows that, if light is emitted from a point where an observer is, then the observer will always find self at the center of the expanding sphere of light, irrespective of the observer's motion.
    A. True;
    B. False.

  56. Are the boxes the same?
    A. Yes;
    B. No.
    two boxes

    Fri 2018 Mar 9:

  57. A fundamental postulate of special relativity is that the speed of light is a universal constant, the same in any inertial frame. What does “speed” mean?

  58. What does “inertial frame” mean?

  59. On your way out to Alpha Cen, you appear to me, watching you through a telescope on Earth, to move at what speed?
    A. 0;
    B. ½ c;
    C. Near c;
    D. 2 c;
    E. Near infinite speed.

  60. On your way back from Alpha Cen, you appear to me, watching you through a telescope on Earth, to move at what speed?
    A. 0;
    B. ½ c;
    C. Near c;
    D. 2 c;
    E. Near infinite speed.

  61. If the round-trip time is 8 years from my (Earth) perspective, then the round-trip time from your (traveler's) perspective is:
    A. less than 8 years;
    B. 8 years;
    C. more than 8 years.

    Mon 2018 Mar 12:

  62. Why does the rotating box (whose edges are moving at near light speed) appear to flex?
    A. Because the speed of light is constant;
    B. Because of Lorentz contraction and time dilation;
    C. Because of gravitational tidal forces;
    D. Because space and time in relativity are curved;
    E. Because it takes light time to travel through the box, so we see the far side as it used to be compared to the near side.

  63. Will the probe fall into the black hole?
    A. Yes;
    B. No.

  64. The horizon radius R of a black hole is proportional to its mass M, while the tidal force at goes M/R3. Therefore the tidal force tearing you apart at the horizon of a black hole is:
    A. Bigger for a more massive black hole;
    B. The same regardless of the mass of the black hole;
    C. Smaller for a more massive black hole.

    Wed 2018 Mar 14:

  65. At the moment you fall through the event horizon of a black hole:
    A. Nothing special happens;
    B. Time appears to freeze, from your point of view;
    C. You get tidally torn apart;
    D. You get incinerated by a burst of intense radiation;
    E. Space and time as you know them come to an end.

  66. According to the waterfall model of black holes, an outside observer cannot see light emitted from inside the event horizon of a black hole because:
    A. Because the black hole curves space inside out;
    B. Space inside the black hole is falling faster than light;
    C. Because light circulates inside a black hole in circular orbits, never getting out;
    D. Because the black hole destroys light, ripping it apart;
    E. Inside a black hole there is no light, just blackness.

  67. From a safe distance, we watch a spherical, pressureless star collapse to a black hole. What will we see?
    A. The star will appear to freeze when at the horizon radius, and never collapse.
    B. The star will appear to branch into a wormhole and white hole, before becoming a black hole.
    C. The star will appear to collapse to a singularity.

  68. When the mass of a black hole increases, its horizon expands. Does the horizon appear to engulf stuff that previously fell through the horizon?
    A. Yes, stuff that previously fell into the black hole disappears.
    B. No, stuff that previously fell into the black hole remains frozen at the horizon, appearing to expand with the horizon.

    Wed 2018 Mar 21

  69. This is a Hubble Space Telescope image of our Galaxy, the Milky Way.
    A. True;
    B. False;
    C. Possibly.
    A galaxy

  70. Near or inside a black hole, you perceive your own time (the time going on inside your brain, or on your wristwatch) to pass:
    A. Much slower than normal;
    B. Normally;
    C. Faster than normal;
    D. Either slower or faster, depending on how you are moving;
    E. The question is meaningless, because time does not exist inside a black hole.

  71. The “No Hair” theorem applies inside a black hole?
    A. Yes;
    B. No.

  72. Is the white hole gravitationally attractive or repulsive?
    A. Attractive;
    B. Repulsive.

    Fri 2018 Mar 23:

  73. The graph of enclosed mass as a function of distance from Sgr A* is flat out to about 1 parsec from the black hole, but then rises. The additional mass comes from:
    A. Uncertainties in the observations;
    B. The black hole;
    C. An accretion disk around the black hole;
    D. Many stars near the center of the Galaxy;
    E. It's a general relativistic effect.

  74. The “No Hair” theorem states that an isolated black hole is characterized by:
    A. Luminosity and Temperature;
    B. Mass and Chemical Composition;
    C. Mass, Electric Charge, and Spin;
    D. Radius and Circumference;
    E. The number and type of singularities.

  75. Which of the following statements about globular clusters is false?
    A. They are gravitationally bound clusters of stars containing typically 10,000 to a million stars;
    B. There about 200 of them distributed in the halo of the Milky Way;
    C. Our solar system is in a globular cluster;
    D. They contain the oldest stars known, about 14 billion years old, as measured from their HR diagrams;
    E. They are composed approximately 75% H, 25% He by mass, with very little heavier elements.

  76. What is dark matter?

  77. How do astronomers detect dark matter?
    A. From its gravitational effects;
    B. From its radio emission;
    C. From its nuclear effects;
    D. From experiments on Earth that attempt to detect weakly interacting particles;
    E. From black holes.

  78. How can the rotation curve of the Milky Way be measured?

    Mon 2018 Apr 2:

  79. What observation established that the “spiral nebulae” are “Island Universes” well outside the confines of the Milky Way?
    A. Kant's 1755 proposal that the spiral nebulae are Island Universes rotating according to Newton's laws;
    B. Henrietta Leavitt's 1907-1912 discovery of Cepheid variables in the Magellanic Clouds;
    C. Vesto Slipher's 1912-1914 discovery that most spiral nebulae are redshifted (not blueshifted);
    D. The 1920 “Island Universe” debate between Harlow Shapley and Heber Curtis;
    E. Edwin Hubble's 1923-1924 discovery of Cepheid variables in the Andromeda galaxy.

  80. What does redshift mean?
    A. A reddening of light by intervening clouds of dust and gas;
    B. A shift of observed spectral lines to longer wavelengths;
    C. An observed dimming of light;
    D. An observed slowing down of the velocity of light;
    E. A pink glow from Ha observed in star forming regions.

  81. Does the Universe have a center?
    A. Yes;
    B. No.

  82. What is the Universe expanding into?

  83. What lies beyond our cosmological horizon?
    A. More Universe, which we don't currently see.
    B. Nothing.

    Wed 2018 Apr 4:

  84. A “Hubble diagram” is a graph of:
    A. Brightness versus wavelength or frequency;
    B. Luminosity versus temperature;
    C. Mass versus radius;
    D. Size versus time;
    E. Distance versus velocity.

  85. Which of the following statements about electron degeneracy pressure is false?
    A. It's a quantum mechanical effect;
    B. Electrons cannot be crushed closer than their wavelengths;
    C. The shorter the wavelength, the higher the electron energy;
    D. Squashed electrons retain this quantum zero-point energy even at zero absolute temperature;
    E. It's what holds up main sequence stars like the Sun against the force of gravity.

  86. Why is thermonuclear burning of electron degenerate matter explosive?
    A. Because when energy is removed from a gravitating system, it heats up;
    B. Because thermonuclear burning is always explosive;
    C. When electron degenerate matter ignites, the temperature increases rapidly without changing the pressure;
    D. Because degenerate electrons get squeezed into protons, forming neutrons and neutrinos;
    E. Because electron degenerate matter is made of iron, which contains no thermonuclear energy.

  87. Thermonuclear supernovae are good “standard candles” — they all have approximately the same brightness. Why?

    Fri 2018 Apr 6:

  88. What is the principal observational evidence that the age of the Universe is about 14 billion years?
    A. The oldest rocks (carbonaceous chondrites) in the solar system indicate an age of 14 billion years;
    B. Radioactive decay of heavy elements created in the Big Bang indicates an age of 14 billion years;
    C. The main sequence turn-off point in the HR diagrams of globular clusters indicates ages of up to 14 billion years;
    D. Light from the most distant galaxies appears to be about 14 billion years old;
    E. The reciprocal of Hubble's constant gives an estimate of the age of the Universe.

  89. How is it that the Hubble diagram of objects at high redshift tell us about the history of the expansion of the Universe?

  90. Why did the 1998 discovery that the Universe is accelerating surprise astronomers?
    A. Because ordinary matter is gravitationally attractive, so should cause the Universe to decelerate;
    B. Because the Universe should expand at a constant rate;
    C. Because clocks on objects at higher redshift appear to us on Earth to run more slowly;
    D. Because thermonuclear supernovae in the young Universe were probably different from those in today's Universe;
    E. Because friction should slow down the expansion.

  91. Which of the following has a spectrum closest to a thermal (blackbody, or Planck) spectrum?
    A. The Sun;
    B. The Orion nebula, a star-forming region;
    C. The Crab nebula, the remnant of the Supernova of 1054;
    D. Cyg X-1, an x-ray binary thought to contain a black hole;
    E. The Cosmic Microwave Background radiation.

    Wed 2018 Apr 11:

  92. What is probably the most important observed feature of galaxies?
    A. A galaxy is a system containing billions of stars;
    B. Galaxies come in a variety of shapes and sizes;
    C. Galaxies are beautiful;
    D. Galaxies are flying away from us with velocity proportional to distance, indicating that there was a Big Bang;
    E. Galaxies collide, but when they do so, the stars do not collide, allowing life in the Universe to continue.

  93. If wavelengths of light stretch with the expansion of the Universe, then the temperature of a thermal (blackbody) spectrum of radiation that expands with the Universe will:
    A. Decrease;
    B. Remain the same;
    C. Increase.

  94. The Local Group of galaxies does not share in the general Hubble expansion of the Universe. Why not?
    A. Because the Local Group contains more matter than average, and its gravity has caused it to start to collapse;
    B. Because the Local Group contains the Milky Way, which is the largest structure in the Universe.
    C. Because the Local Group is in a special place at the center of the Universe;
    D. Because the Local Group is older than more distant galaxies;
    E. Because Hubble's law does not apply to the Local Group.

  95. Which of the following is not a common consequence of a collision or near collision between galaxies?
    A. Individual stars collide;
    B. Bursts of star formation;
    C. Spiral density waves may be excited;
    D. Tidal tails;
    E. Spiral galaxies may lose their disks and become Ellipticals.

    Mon 2018 Apr 16:

  96. Which of the following statements about the Cosmic Microwave Background (CMB) is false?
    A. It has a thermal (or blackbody, or Planck) spectrum to exquisite accuracy;
    B. After correcting for our motion through it, the CMB is isotropic to a few  10-5;
    C. The CMB comes to us from the epoch of Recombination, when the temperature cooled through the temperature 3,000 K at which Hydrogen becomes neutral;
    D. The temperature of the CMB today is comparable to the temperature at the center of the Sun, about 107 Kelvin;
    E. It is one of the main evidences in favor of the hot Big Bang.

  97. An astronomer observes a galaxy at redshift \(z = 1\). The Universe at the observed galaxy was:
    A. Half its current size;
    B. Twice its current size;
    C. Half its current age;
    D. Twice its current age;
    E. Expanding at twice its current rate.

  98. Which of these universes is spatially flat?

    A. \(\Omega_{\rm m} = 0.3\), \(\Omega_\Lambda = 0.7\) (red, top curve);
    B. \(\Omega_{\rm m} = 0.3\), \(\Omega_\Lambda = 0.0\) (blue, 2nd curve);
    C. \(\Omega_{\rm m} = 1.0\), \(\Omega_\Lambda = 0.0\) (green, 3rd curve);
    D. \(\Omega_{\rm m} = 5.0\), \(\Omega_\Lambda = 0.0\) (orange, bottom curve);
    E. Both A and C.
    Cosmic scale factor versus time for various models

  99. Why is it puzzling that the temperature of the CMB on opposite sides of the sky today is the same?

    Wed 2018 Apr 18:

  100. Planck image of CMB In the Planck satellite image of the CMB at right, the 1° size of the blobs is roughly the size of:
    A. a star-forming region;
    B. a galaxy;
    C. a supercluster of galaxies;
    D. the horizon at Recombination;
    E. the current horizon distance.

  101. What was the size of the horizon at Recombination, when the age of the Universe was about 400,000 years old?
    A. About 400 lightyears;
    B. About 400,000 lightyears;
    C. About 4 billion lightyears;
    D. About 14 billion lightyears;
    E. About 140 billion lightyears.

  102. What is the size of the horizon today?
    A. About 400 lightyears;
    B. About 400,000 lightyears;
    C. About 4 billion lightyears;
    D. About 14 billion lightyears;
    E. About 140 billion lightyears.

  103. Planck + WMAP + ACT + SPT power spectrum What observational evidence suggests that the Universe is flat?
    A. The expansion of the Universe;
    B. The acceleration of the Universe, indicating that there is gravitationally repulsive Dark Energy;
    C. The astonishing uniformity of the Cosmic Microwave Background;
    D. The near thermal (blackbody, Planck) spectrum of the CMB;
    E. The position (harmonic number) of the first peak in the power spectrum of fluctuations in the CMB.

    Wed 2018 Apr 25:

  104. One piece of observational evidence that the Universe shortly after the Big Bang was much simpler than it is today is the astonishing uniformity of the Cosmic Microwave Background. What other piece of observational evidence suggests that the Universe used to be much simpler than it is today?
    A. The expansion of the Universe;
    B. The acceleration of the Universe, indicating that there is gravitationally repulsive Dark Energy;
    C. The abundance of elements in the Universe (mostly 75% H, 25% He by mass);
    D. The near thermal (blackbody, Planck) spectrum of the CMB;
    E. The position (harmonic number) of the first peak in the power spectrum of fluctuations in the CMB.

  105. The Cosmic Scale Factor is:
    A. About 15 gigalightyears;
    B. The ratio of the actual density of the Universe to the critical density;
    C. Another name for the Hubble constant;
    D. A measure of the size of the Universe, which expands with the Universe;
    E. The distance to the horizon of the Universe.

  106. Is the vacuum energy posited by Inflation the same as the Dark Energy measured in the Universe today?
    A. Yes;
    B. No;
    C. Possibly.

  107. Planck image of CMB What is the horizon problem?
    A. Does our observable Universe have a horizon?
    B. How far away is the horizon?
    C. What lies beyond the horizon?
    D. We cannot see the horizon, because the Cosmic Microwave Background gets in the way.
    E. How can regions of the CMB more than 1 degree apart, which were causally disconnected at the time of Recombination, know to have the same temperature today?

  108. Which of the following is not one of the four forces that appears to govern all the interactions between particles in nature today:
    A. Gravity;
    B. Electromagnetism;
    C. The light force;
    D. The weak force;
    E. The strong (or nuclear, or color) force.

    Fri 2018 Apr 27:

  109. Which of the following is not explained by the theory of Inflation?
    A. Why the Universe is expanding;
    B. Why the Universe is almost spatially flat (within 0.5%, according to observations of the CMB by the Planck satellite, 2015);
    C. The horizon problem (How can regions of the Cosmic Microwave Background more than 1 degree apart, which were causally disconnected at the time of Recombination, know to have the same temperature today?);
    D. Where the matter and radiation in today's Universe came from;
    E. What determines the laws of physics.

  110. The leading candidate for gravitationally attractive Dark Matter is:
    A. Stars and gas;
    B. Planets;
    C. Black holes;
    D. Aliens;
    E. Non-baryonic dark matter so far undetected in the lab.

  111. The matter causing gravitational lensing in rich cluster of galaxies is mostly:
    A. Stars and gas;
    B. Supermassive black holes;
    C. Mysterious dark matter;
    D. Dark energy;
    E. Cosmic microwave background.

  112. Which of the following does not contain substantial amounts of "Dark Matter"?
    A. The Solar System;
    B. The Milky Way;
    C. The Local Group;
    D. The Local Supercluster;
    E. The Universe.

    Mon 2018 Apr 30:

  113. Would you vote in favor of making a baby Universe?
      3 A. I think that it is immoral to attempt to make a baby Universe. I vote no.
      4 B. If this is the only way that our Universe can reproduce, then I think society has a moral duty to make it happen. I vote yes.
      9 C. I don't think society should waste resources attempting to make a baby Universe. I vote no.
    14 D. I don't have a strong moral opinion, but I support the notion that society should attempt to make a baby Universe. I vote yes.
      2 E. I don't really care either way. I probably won't bother to vote.

  114. If society were presented with the one-time opportunity to make a baby Universe, what do you think the eventual outcome would be?
      8 A. All out war between the yes and no factions.
      4 B. Fierce political discussion, resolved by the democractic process.
    18 C. Fierce political discussion, leading to deadlock.
      2 D. Nothing. Society would not care, and would just go about its business.

  115. You are the leader of the “No-baby-Universe” faction. You believe deeply that your cause is right. You strive for right. But your faction has lost the vote. What do you do?
    10 A. Continue to argue non-violently for your cause.
    12 B. Fight for right. Start a guerilla war.
      7 C. Spread disinformation about your opponents and their theory of making baby Universes.
      3 D. Something else.

  116. How should the movie end?
    A. As the science says: the people outside the black hole never know whether a baby Universe was made, or what might be the nature of that baby Universe.
    B. The baby Universe should expand out into the old Universe, destroying it, and starting afresh.
    C. Somehow there is an unexpected line of communication from inside the black hole to outside, that allows people outside the black hole to discover what happened.
    D. Postpone the conclusion to a sequel.
    E. Something else.

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