ASTRONOMY 1 EXAM 3 a Name Identify Terms - Matching (20 @ 1 point each = 20 pts.) Multiple Choice (25 @ 2 points each = 50 pts.) Essays (choose 3 of 4 @ 10 points each = 30 pt 1.Luminosity D 8.White dwarf I 15.Spectral class E 2.Proton-proton chain G 9.coulomb barrier O 16.Energy transport J 3.Neutrino L 10.Parsec Q 17.Conservation of R 4.Chandrasekhar Limit B 11.Nuclear fission energy 18.Interstellar medium CorP 5.Binary star N 12.Nuclear fusion AorM 19.Light curve H 6. Zero-age main sequence S 13.Absolute visual D 20.Nebula CorP 7.Spectroscopic binary K magnitude 14.Stellar parallax F A. Nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy. B. Approximately 1.4 times the mass of the sun; any white dwarf with less than this mass will stay a white dwarf forever, while a star that exceeds this mass is destined to end its life in that most violent of explosions: a supernova C. Interstellar cloud of dust, hydrogen, helium and other ionized gases. D. The intrinsic brightness of a celestial object (as distinct from its apparent brightness diminished by distance). E. A classification of stars. In order of decreasing temperature, O, B, A, F, G, K, and M. F. The apparent shift of position of any nearby star (or other object) against the background of distant objects G. One of the two (known) sets of fusion reactions by which stars convert hydrogen to helium. H. A graph of light intensity of a celestial object or region, as a function of time. I. A small very dense star that is typically the size of a planet J. A mix of Radiation & Convection transports energy from the core to the surface of a star. K. A binary star whose components are identified by periodic Doppler shifts of the system's spectral lines as the orbital motion along the line of sight alternates toward and away from Earth. L. A neutral subatomic particle with a mass close to zero and half-integral spin, rarely reacting with normal matter. M. A nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy. N. A system of two stars in which one star revolves around the other or both revolve around a common center. O. The energy barrier due to electrostatic interaction that two nuclei need to overcome so they can get close enough to undergo a nuclear reaction. P. The matter and radiation that exists in the space between the star systems in a galaxy. Q. A unit of distance used in astronomy, equal to about 3.26 light years (3.086 10 13 kilometers) R. A principle stating that energy cannot be created or destroyed, but can be altered from one form to another. S. The time when a star first joins the main sequence on the Hertzsprung-Russell diagram (HR diagram) by burning hydrogen in its core through fusion reactions.
Note: There is a HR diagram at the end of the Multiple choice questions which may be helpful in answering some questions. 1. What type of star is our Sun? a) A white dwarf b) A pulsar c) A main sequence star d) A red giant 2. The energy source for the sun is a) combustion of hydrocarbons b) solar flares c) nuclear fission, the splitting of two hydrogen atoms d) nuclear fusion, the joining of two hydrogen atoms e) combustion of hydrogen 3. The average star spends of its lifetime on the main sequence. a) 1% b) 2% c) 10% d) 20% e) 90% 4. What causes the outward gas pressure that balances the inward pull of gravity in a main sequence star? a) The rapid outward flow of gas. b) The rapid inward flow of the gas. c) The high temperature of the gas. d) The high density of the gas. e) c and d 5. What is the lifetime of a 15 solar mass star on the main sequence? Estimate using table 9-2 a) 8 10 ⁹ yrs b) 11 million years c) 1 million years d) 3 10 ⁹ yrs 6. Interstellar gas clouds may collapse to form stars if they a. have very high temperatures b. encounter a shock wave. c. rotate rapidly d. are located near main sequence spectral type K and M stars. 7. Why do higher mass stars live shorter lives on the main sequence than lower mass stars? a. Higher mass stars burn through their nuclear fuel faster. b. Lower mass stars don't get their energy from that same nuclear fusion source as higher mass stars. c. Higher mass stars have less hydrogen fuel to burn. d. Lower mass stars spend a longer time evolving to the main-sequence. e. All of the above are false.
8. The condition of means that the force due to gravity pushing down on a layer is exactly equal to the pressure pushing outward on that layer. a. balance b. Hydrostatic equilibrium c. Coulomb barrier d. Bipolar Flow 9.The lowest-mass stars cannot become giants because a. they do not contain helium b. they rotate too slowly c. they cannot heat their centers hot enough. d. they contain strong magnetic fields. e. they never use up their hydrogen. 10.How does the Sun produce the energy that heats our planet? a. The gases inside the Sun are burning and producing large amounts of energy. b. Gas inside the Sun heats up when compressed, giving off large amounts of energy. c. Heat trapped by magnetic fields in the Sun is released as energy. d. Hydrogen is combined into helium, giving off large amounts of energy. e. The core of the Sun has radioactive atoms that give off energy as they decay. Goofy Star has an absolute magnitude of +8.0 and belongs to spectral type K. Daffy Star has an absolute magnitude of -2.0 and belongs to spectral type K. Use this information to answer the following two questions. 11. Which of the following is true about the color of the two stars? a. Goofy Star would appear blue. b. Daffy Star would appear blue. c. They would both appear the same color. d. There is not enough information to determine this. 12. Which star has the largest surface area? a. Goofy Star b. Daffy Star c. They have the same surface area. d. There is not enough information to determine this. 13. A star's luminosity depends only on the star's a. distance and diameter. b. temperature and distance. c. distance. d. temperature and diameter. e. apparent magnitude 14. In an H-R Diagram, stars with the smallest radius are found in the of the diagram. a. center b. upper left corner c. upper right corner d. lower left corner e. lower right corner
15. In a binary system, the more massive star a. is at the center of mass. b. is farthest from the center of mass. c. is nearest the center of mass. d. follows the largest orbit. e. shows a larger Doppler shift in its spectral lines. 16.If two stars are emitting the same amount of light, the star that is farther will appear a. brighter. b. dimmer. c. redder. d. bluer. e. They will have the same brightness as seen from Earth. 17. A star with a luminosity of 10 4 has approximately a. 1 solar mass b. 5 solar masses c. 20 solar masses d. 5 solar masses 18. The star Krok has an apparent magnitude of +0.03 and an absolute magnitude of +3.0. If it were moved 10 times farther from Earth as it is now, which one of the following would occur? a. absolute magnitude number would decrease (gets smaller) b. apparent magnitude number would decrease (gets smaller) c. apparent magnitude number would stay the same d. absolute magnitude number would increase (gets bigger) e. apparent magnitude number would increase (gets bigger) 19. Which of the following statements is always true of any two stars (including Red Giants and White Dwarfs) that have the same absolute magnitude? a. They have the same temperature. b. They have the same luminosity. c. They have the same spectral type. d. They have the same surface area. e. They have the same mass. 20. During the beginning of star formation, the force that dominates the collapse of a cloud of gas and dust is a. electrostatic b. gravity c. magnetic d. friction
21.According to the diagram, the life cycle path followed by a star is determined by the star s initial a. mass and size b. temperature and origin c. luminosity and color d. luminosity and structure 22. Stars like Earth s Sun most likely formed Directly from a a. nebula b. red giant c. supernova d. black dwarf 23.According to the diagram, a star like Earth s Sun will eventually a. explode in a supernova b. become a black hole c. change into a white dwarf d. become a neutron star 24.Which statement describes the general relationship between the temperature and the luminosity of main sequence stars? a. As temperature decreases, luminosity increases. b. As temperature decreases, luminosity remains the same. c. As temperature increases, luminosity increases. d.as temperature increases, luminosity remains the same 25.Which star color indicates the hottest star surface temperature? a. blue b. yellow c. white d. red
Essays Choose 3 of the 4 topics to write a short essay 1. How can we find the distance to a star that is too distant to have a measurable parallax? Astronomers have to use a technique called 'spectroscopic parallax' to determine distance to stars too far away for simple parallax measurements. The spectrum of such a distant star and its luminosity will reveal its classification (O,B,A,F,G,K,M,N). The next step is to find where the subject star lies on the HR diagram. The HR diagram will reveal the apparent magnitude of the star along with its absolute magnitude, and from that its distance can be computed. 2. Why are Balmer lines strong in the spectra of medium-temperature stars and weak in the spectra of hot and cool stars? First, Balmer lines are primarily in the visual region of the absorption line spectrum of stars. They are created by jumps to less bound levels from level number 2. Electrons have to be in level number 2 for the absorption lines to be created. The number of electrons in different levels depends on the temperature of the star. Lower temperature stars have most electrons in level 1, medium in level 2, and high temperature in level 3. Therefore only medium-temperature stars have lots of electrons in level 2 needed to create Balmer absorption lines. 3. Step-by-step, explain how energy flows from the center of the sun to Earth. Energy in the form of heat, light and other radiation begins in the core of the sun, where hydrogen atoms are being smashed together to form helium. This releases a great deal of energy which moves through the sun's radiation zone up through it's convection zone, where some of the energy and gases cool a bit and sink, only to be reheated to rise again. Eventually, much of this energy (photons of light, heat and solar radiation called "solar wind") reaches the upper layer of the sun's surface, called the photosphere. Radiation from the photosphere then radiates out through the troposphere to the corona. From the corona, photons of light, heat energy and other solar radiation leaves and most of it diffuses into space, but a small percentage reaches Earth about 8 minutes after it left the sun. 4. Explain the sequence of events between a star the size of our sun joining the main sequence and becoming a white dwarf. A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form helium. The helium core then starts to contract further and reactions begin to occur in a shell around the core. The core is then hot enough for the helium to fuse to form carbon. The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant. The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula. The remaining core (thats 80% of the original star) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims. When it stops shining, the now dead star is called a Black Dwarf.