Astronomy Hour Exam 2 March 10, 2011 QUESTION 1: The half-life of Ra 226 (radium) is 1600 years. If you started with a sample of 100 Ra 226

Transcription

1 Astronomy Hour Exam 2 March 10, 2011 QUESTION 1: The half-life of Ra 226 (radium) is 1600 years. If you started with a sample of 100 Ra 226 atoms, approximately how many Ra 226 atoms would be left 3200 years later? a) 200. b) 100. c) 50. d) 25. e) 0. QUESTION 2: Olber s Paradox is related to: a) How can the Universe expand when there is nothing to expand into? b) How could the Universe have once fit into a single point? c) How can the speed of light not depend on the velocity of the source? d) Why does light bend in a gravitational field? e) Why is (most of) the sky dark? QUESTION 3: The most common element in the Universe is: a) Hydrogen. b) Helium. c) Carbon. d) Iron. e) Silicon. QUESTION 4: An isotropic universe is one which: a) Is expanding equally in all directions. b) Is the same everywhere. c) Started from a single point. d) Looks the same at all distances. e) Looks the same in all directions. QUESTION 5: Penzias and Wilson were studying microwave radiation from space because: a) They had a telescope that could do that and they wanted to use it. b) They were looking for the cosmic microwave background radiation. c) They were studying the effect of pigeon poop on antennae. d) They were studying the noise to be encountered when communicating with microwaves. e) They had nothing to do with studying microwave radiation from space. QUESTION 6: Properties of the cosmic microwave background radiation include: a) It follows a black body spectrum and it is nearly the same in all directions. b) It follows a black body spectrum and depends strongly on direction. c) It is nearly the same in all directions and it shows hydrogen emission lines. d) It shows hydrogen emission lines and it is nearly the same in all directions. e) It is isotropic random noise. QUESTION 7: Approximately when do scientists believe the universe began? a) 4047 BC. b) One billion years ago. c) 14 billion years ago. d) 62 billion years ago. e) It had no beginning. QUESTION 8: According to the Equivalence Principle, gravity is equivalent to: a) Curvature. b) Net force. c) Electric force. d) Acceleration. e) The state of free-fall. 1

2 2 QUESTION 9: In a curved space: a) The sum of the interior angles of a triangle = 180. b) The shortest distance between two points is a straight line. c) Two parallel lines never meet. d) All of the above. e) None of the above. QUESTION 10: Airlines take great circle routes for long-distance travel because: a) It is the shortest route. b) It is the route that keeps the direction of travel constant. c) It minimizes the amount of time over water. d) It takes maximum advantage of the jet stream. e) Airlines do not take great circle routes. QUESTION 11: You are drugged and then awake in a closed room. You do not know where you are. You drop your flashlight and notice that it falls straight downward with an acceleration of 9.8 m/s 2. This shows that you are: a) Stationary in a gravitational field. b) Stationary or moving with a constant velocity in a gravitational field. c) Accelerating upward at 9.8 m/s 2. d) Accelerating downward at 9.8 m/s 2. e) You could be accelerating upward or in a gravitational field or a combination of both. QUESTION 12: The Equivalence Principle is: a) Known to be true because it is a principle. b) Taken as true because Einstein proposed it. c) Just a scientific theory, capable of being proven wrong. d) Not a scientific theory because it involves thought experiments. e) Capable of being proven true. QUESTION 13: Hubble developed his famous law, using what information about galaxies? a) Distances and redshifts. b) Diameters and redshifts. c) Luminosities and redshifts. d) Shapes and redshifts. e) Velocities and redshifts. QUESTION 14: The distance to quasars are measured by: a) Observing Cepheid variable stars in them. b) Determining their redshifts. c) The Tully-Fisher relation. d) Parallax. e) Observing supernovae in them. QUESTION 15: If you measure the redshift of two distant galaxies and find that galaxy A is moving away from us at 15,000 km/s and galaxy B is moving away at 60,000 km/s, then you can conclude that: a) Galaxy A is twice as far away as galaxy B. b) Galaxy B is twice as far away as galaxy A. c) Galaxy A is four times farther away than galaxy B. d) Galaxy B is four times farther away than galaxy A. e) Galaxy A is less bright than galaxy B. QUESTION 16: Which of the following statements is true about virtually all galaxies compared to the Milky Way galaxy: a) They are older. b) They are larger. c) They are smaller. d) They are moving away from the Milky Way. e) They rotate slower.

3 3 QUESTION 17: What keeps light from escaping a black hole? a) A photon sphere that reflects all light. b) The event horizon, which is an opaque sphere. c) Gravity. d) An ultrastrong magnetic field. e) Nothing light can escape from a black hole along the field lines. QUESTION 18: How can we detect a black hole? a) Gamma rays, being the most energetic type of electromagnetic radiation, will escape and can be detected. b) Observing the effects of the strong gravitational force on nearby objects. c) The gravitational force is equal to and opposite to the centrifugal force. d) It emits a black body spectrum. e) The gravitational force is equal to and opposite to the outward pressure. QUESTION 19: Because almost all galaxies are redshifted, we know that: a) We are near the center of the universe. b) There was no beginning of time. c) There is dark matter in the universe. d) There is dark energy and dark matter in the universe. e) The universe is expanding. QUESTION 20: Gravity waves: a) Are not believed to exist. b) Have been detected. c) Are so weak they can never be detected. d) Are very difficult to observe but are searches for them are underway. e) Are detected during earthquakes. QUESTION 21: How can the age of the universe be estimated from Hubble s Law? a) From the velocity and distance to galaxies, we can estimate the time it took them to reach their present positions after the Big Bang. b) By seeing the most faraway galaxies, the distance in light-years tells us how old the universe is. c) From the distance and velocity of distant galaxies, we can estimate how much time was needed to accelerate them to their present velocities. d) By measuring how long it took the light to get to us from the edge of the universe. e) There is no way to do this. QUESTION 22: Which of the following is Hubble s Law? a) The faster a galaxy spins, the larger it is. b) The greater the distance to a galaxy, the fainter it is. c) The greater the distance to a galaxy, the faster it is receding from us. d) The more distant a galaxy is from us, the younger it looks. e) The younger a galaxy appears, the higher its luminosity. QUESTION 23: Vesto Slipher found that the spectrum from the Andromeda nebula is blue-shifted. This means that: a) Andromeda is rotating rapidly. b) Andromeda is an active galaxy. c) Andromeda contains many young stars. d) Andromeda is moving away from us. e) Andromeda is moving towards us. QUESTION 24: Why do virtually all galaxies in the universe appear to be moving away from us? a) We are located near where the Big Bang occurred. b) We are located near the center of the universe. c) Observers in all galaxies see the same thing because of the expansion of the universe d) They aren t moving away from us, we are moving away from them e) The statement is false: most galaxies do not appear to be moving away from us.

4 4 QUESTION 25: What is the origin of the Cosmic Microwave Background: a) Electromagnetic radiation remaining from the Big Bang. b) Dirt in microwave antennae. c) Quasars. d) Pulsars. e) Blackbody radiation from distant galaxy superclusters. QUESTION 26: The spectral shape of the cosmic microwave background radiation is: a) The sum of spectra for hydrogen and helium. b) The same as the spectrum of the Sun. c) A black body spectrum with a temperature of 2.7K. d) A flat spectrum. e) An absorption spectrum. QUESTION 27: How do gravitational lenses occur? a) Gravity curves space and light follows this curvature. b) Interstellar gas bends light like glass does. c) Light can be scattered by intense radiation from quasars. d) The cosmic microwave background radiation causes light to curve. e) It doesn t occur, as gravitational lenses have not been observed. QUESTION 28: The existence of dark energy shows that: a) The Universe is expanding. b) There is unobserved mass in the Milky Way. c) Space is curved near a black hole. d) Gravitational waves exist. e) Hubble s Law is not correct at large distances. QUESTION 29: Edwin Hubble s discovery of a Cepheid variable in the Andromeda nebula showed that: a) The Andromeda nebula is not part of the Milky Way galaxy. b) The Andromeda nebula contains dark matter. c) The Andromeda nebula is red-shifted. d) The Andromeda nebula is moving towards us. e) The Universe is flat. QUESTION 30: A galaxy is at a distance of one billion light years. Which of the following is true? a) We see the galaxy the way it will be in one billion years b) We see the galaxy the way it was one billion years ago c) We see the galaxy the way it was when the universe was one billion years old d) We see what our galaxy will be like in one billion years e) We have no knowledge of anything at that distance QUESTION 31: Dark energy is: a) Unobserved matter that explains galactic rotation curves. b) The energy released when a mass falls into a black hole. c) The source of the enormous energies emitted by quasars. d) An unknown force that accelerates the expansion of the universe. e) What Darth Vader used to combat Luke Skywalker. QUESTION 32: We believe that the Milky Way galaxy has a supermassive black hole at its center. Evidence for this comes from: a) The study of the motion of stars near the Galactic center. b) The study of gamma rays coming from the Galactic center. c) The direct observation of the black hole. d) Observation of the black body radiation from the Galactic center. e) There is no evidence for a supermassive black hole at the center of the Galaxy.

5 5 QUESTION 33: The velocity an object would need to escape a black hole is: a) Not definable. b) Infinite. c) Equal to the velocity of light. d) Less that but almost equal to the velocity of light. e) Greater than or equal to the velocity of sound in the black hole. QUESTION 34: As light falls into a black hole, it will: a) Shift to longer wavelengths. b) Shift to shorter wavelengths. c) Speed up due to the curvature of the space. d) Continue to travel in a straight line. e) Pass through the black hole and emerge from the other side. QUESTION 35: In general relativity, gravity results in: a) Time warps. b) Curved space. c) Nuclear fusion. d) The strong nuclear force. e) The equivalence principle. QUESTION 36: The main energy source in a quasar is: a) Nuclear fusion. b) Nuclear fission. c) Mass falling in towards a supermassive black hole. d) Combustion of hydrogen. e) A quasar does not produce any energy. QUESTION 37: The most distant galaxies observed have redshifts that, when interpreted as Doppler shifts, indicate they are receding from us with velocities several times the speed of light. a) This is possible because we are observing the cosmological redshift. b) As this is forbidden by the theory of special relativity, that theory must be wrong. c) As this is forbidden by the theory of special relativity, the observations must be wrong. d) This is allowed for quasars as they contain a black hole. e) The statement is false there are no such observations. QUESTION 38: The observable universe is: a) Everything that isn t hidden by dust. b) Everything within a sphere centered on the Earth with a radius of 14 billion light-years. c) All objects that are bright enough to be seen. d) Everything that was within a sphere centered on the Earth with a radius of 14 billion light-years when it emitted light. e) Everything except dark matter. QUESTION 39: Why are quasars used to examine the validity of Hubble s Law at large distances? a) Because they are so bright. b) Because they are so far away. c) Both a) and b). d) Because they have a black hole at their center. e) Quasars are not used to examine the validity of Hubble s Law at large distances.

6 6 QUESTION 40: Sir Arthur Eddington confirmed a key prediction of general relativity by which observation? a) He observed the bending of light by a gravitational field during a solar eclipse. b) He observed the bending of light by a gravitational field by observing a gravitational lens. c) He detected a black hole by observing the orbits of nearby objects. d) He discovered the cosmological constant by studying the red shift of quasars. e) He discovered a black hole in Cygnus X-1. QUESTION 41: Homogeneity and isotropy, taken as assumptions regarding the structure and evolution of the universe, are known as: a) Olbers Paradox b) Hubble s Law c) The Friedmann equation d) The Cosmological Principle e) The Grand Unified Theory QUESTION 42: The cosmic microwave background is important mostly because: a) Its detection lead to the discovery of dark energy b) Its detection opened a new form of radiation to observation c) It confirmed a major prediction made by the Big Bang theory d) It showed that the universe is open e) It showed that the universe is closed QUESTION 43: The periodic table refers to: a) An arrangement of the chemical elements grouping elements with similar properties. b) A table telling how to relate luminosity and periods of Cepheid variables. c) The theory in which the Universe undergoes repeated expansions and contractions. d) A chart of the Earth s tides. e) A chart of the positions of the planets. QUESTION 44: The atomic number of an atom is equal to: a) The number of protons. b) The number of protons + the number of neutrons. c) The number of neutrons. d) The number of protons + the number of neutrons + the number of electrons. e) The number of atoms in a mole. QUESTION 45: The chemical properties of an element are determined by: a) The atomic weight. b) The arrangement of the protons in the nucleus. c) The number of neutrons. d) The particular isotope of the element. e) The atomic electrons. QUESTION 46: The Einstein equation of general relativity relates: a) The Doppler shift to the velocity of the light source. b) The equivalence of energy and mass. c) The cosmic microwave background spectrum to the temperature of the universe. d) The curvature of space-time to the distribution of matter and energy in space-time. e) There is no Einstein equation in general relativity. QUESTION 47: Nearly all of the space in an atom is taken up by: a) The nucleus. b) The electrons. c) The protons. d) Empty space. e) Electron bonds.

7 7 QUESTION 48: Hubble s constant measures: a) The density of galaxies in the universe. b) The luminosity of distant galaxies. c) The reddening of light from gravitational fields. d) The radial velocity of a galaxy. e) The rate of expansion of the universe. QUESTION 49: If the Sun were magically to turn into a black hole of the same mass: a) The Earth would start to spiral inward. b) The Earth would be quickly sucked into the black hole. c) The Earth s orbit would be unchanged. d) The Earth would fly off into space. e) The Earth would be torn apart by the black hole s gravitational field. QUESTION 50: The distribution of galaxies in the universe is: a) Completely uniform. b) Denser close to us compared with farther away. c) Denser far away from us compared with close by. d) Characterized by large-scale structures such a voids and walls. e) We can t tell because we can t see in all directions. QUESTION 51: What is the average temperature of the universe? a) It is not well defined: it depends on which direction you are looking. b) 300 K. c) 0 K d) 2.7 K e) 0 C QUESTION 52: Black holes can result from which phenomenon? a) Gravitational collapse of very large stars. b) Novae. c) An accretion disk. d) Core collapse of a 1 solar-mass star. e) Pulsar spin-up. QUESTION 53: Cygnus X-1 is a binary system consisting of an ordinary star and a black hole orbiting about each other. Matter from the star falling into the black hole forms: a) An accretion disk. b) A neutron star. c) A pulsar. d) A quasar. e) Cepheid variable. QUESTION 54: According to relativity, what can go faster than the speed of light? a) Nothing. b) Only energy. c) Gravitational waves. d) The expansion of space. e) The event horizon of a black hole. QUESTION 55: Properties of quasars include: a) They are very bright, compact, and very far away. b) They have small redshifts. c) They are very bright, very far away, and have unusual rotation curves. d) They are very bright and always form gravitational lenses. e) They are the rare objects that appear to be moving towards us. QUESTION 56: Why does light bend in a curved space? a) Light is attracted by a large mass. b) Light doesn t bend in a curved space; it travels in straight lines. c) Light has to bend around a large mass because it cannot pass through it. d) Light follows a geodesic, which is curved in a curved space. e) Photons are accelerated by the gravitational field.

8 8 QUESTION 57: Which of the following is the correct picture of the expansion of the universe? a) Galaxies are moving away from each other through empty space. b) All distance scales increase as the universe expands. c) The redshift of light from distant galaxies is a Doppler shift. d) As the universe expands, so do objects within the universe such as clusters of galaxies. e) The observed redshift from distant galaxies is due to the increase in the wavelength of light as the space through which it travels expands. QUESTION 58: The mass of an atom is almost entirely determined by: a) The atomic number. b) The number of electrons. c) The number of protons. d) The number of neutrons. e) The number of protons + the number of neutrons. QUESTION 59: In a black hole, the event horizon is: a) Smaller than the size of the black hole. b) Larger than the size of the black hole. c) Equal to the size of the black hole. d) Independent of the black hole mass. e) Equal to 0.1 AU. QUESTION 60: In coming to the conclusion that light beams are bent by gravity, Einstein reasoned that: a) Because all observers experience the same laws of physics, Newton's theory of gravity must apply to light beams. b) Because light speed is the same for all observers, moving observers would observe that light beams bend. c) Fast-moving observers would find that light beams bend, so gravity must also bend light beams. d) Accelerated observers would find that light beams bend, so gravity must also bend light beams. e) Einstein did not believe that gravity bends light.