Exam 2 Example - 54/5 Exam#2 Stars and Galaxies...

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Unformatted text preview: 54/5; Exam #2 Stars and Galaxies Introduction to Astronomy course Fall 2012 . This exam has few short answers, multiple questions, which are each worth 1 point, problems, which are worth 3 points each, and two ~ essay questions (that are NOT mandatory — just extra credit if you answers are correct). Take your time to read carefully each question. For the math problems show your work in order to receive points. z 1. You locate the constellation Cygnus into the hi ht sky. You identify that the l L brighter star is Deneb (which is al called Al'ig —using Bayer system). 2 points - 2. Cygnus is crowded with stars and ' luminous gas clouds along the plane of our Milky Way Galaxy. Define the main characteristics of this part of our galaxy-4 points- "??? Omar $AV’“ s 3- Deneb 1s a white class A supergiant. What IS the main characteristic of the spectrum that we would have from a star with this spectral classification?- ( 4 points-) a flu, Marx simmer??? ' l "33$ng 5 l‘ Wig 9“ Gail Ceramic :5 “ . “ ’" (1de ti iii $363146} “ xig ,i 1: ,1 f; 4. Deneb, the brightest star in Cygnus has a luminosity 3 2X10 =3 and a surface temperature of 9500K. The apparent Visual magnitude of Deneb IS m=+1. 25 and thigabsolute magnitude 1s — 8. 75. Calculate how big 1S Deneb’ s radius in comparison with our Sun and its distance from us. What type of radiation the star tilts“; emitting ( What 1s the wavelength)?( 6 points) i; 3531. J 33% T e , .3 l 53 51363 M... _ % :3‘9330} We“; ‘/ g <. 5. FIGURE 1 is a spectrum of a galaxy at rest. (3 p01‘ we“ WWWW“ ”i Figure 1 Intensity 8000 4000 Wavelength (A) 7; { ‘7 Draw the spectrum of a NEARBY galaxy that is coming towards you. Intensity 3000 4000 Wavelength {all} 1 . . 54y >5;ij ‘5“ 6. Proxima Centauri isma small red dwarf star that radiates most strongly at a wavelength of about 35 00mm. How hot is the surface of the star? Its luminosity is 1/ l 0000 the Sun’s luminosity. Calculate the radius of this star.( 6 points) Answer w 15 -0.5 0.0 0.5 1.0 1.5 B Vim] 2.0 7. Define What a H— R diagram is and how is helping us to understand star’s stages evolution ( 6 points) :25 3.15 A Anamw $52525 and nae; a 5mg 5::quch 4W JKW fiffifl‘LUVé \ifi i‘i’é WAmW‘xOS N . Vwfl l5§€jl(\4\fi:fij CL"? 5““ f i 5 A i! a {3 ii i: :4 5} if 55%;”; r? by}; g 51“» U»! Qifii )“R‘gg” C a r Ce“ 5% V 5 ~ «5 ,5 hm “v05 55”; 515 W A: SAC. 55% 54 A A max Sigma”; AE‘giAF‘" “i'i/if. was??? figgjé “Swag iii"? '3'? gm $1an Emir ii? «7' indict? § 53% Use the following table for the next uestions: fie ~ f — A- uarent Magnitude Absolute Magnitude —__ 0 2 ‘ 5 4 8. Which star appear brighter from Earth: Star C, Star D or neither? Explain.(2 points) :35; if: MEN“ Wm} 33% ifiliiié 5 _ Sflewm {WEE his: @1343.) 0 Z M»? if} “maxi- tvi‘tg if)” GE?" 5.}; 51695???“ ii; 5 i’ 3%}? D . fin {h E k x \ k' A“ . . “ififivijy i" a? e‘i‘fii‘é’g §Wiiv§ Wifiifi‘idéég. 9. Which object is more luminous? Explain your answer.( 2 points) gSTifi 13:,QCHQ EWQQU‘Q bang SQERMQ ix? iiwi‘fxfifiii’w‘ kw“ Wwfi K" ‘x " i ‘ s v, .3 , . '3, ~,»_ if , i , ' ', ““333, ,, 1!: q/i V {ifiaéowwwi iiixstiifiimiri {ii 0'9 are (1:ng any! , «fiigifii f” iii-"$6 Line.- “ ”5:32“ i 4%! m“ ‘- , , i 1" __ , ‘7 \ Multi le uestions ‘ fwg’ffia {girl-(”(3 {R¥‘¢§Q.V\:¥ Cal" 139% iii H3 {viii irifliiii i/I/Dgeiiiflfifl if 1. You photograph a reglon of the night sky in March, in September, and again the following March. The two March photos look the same, but the September photo shows three stars in different locations. The star whose position shifts the most must be a) farthest away. closest. c receding from Earth most rapidly. (1) just passing through the Galaxy 2. The luminosity of a star is : . Another name for its color or surface temperature b ts total energy output into all space, over all wavelengths 0 .Its brightness as seen by people on Earth d).Its brightness if it were to be at a distance of 10 parsecs from Earth 3. A star with a continuous spectrum shines through a cool interstellar cloud composed primarily of hydrogen. The cloud is falling inward toward the star (and away from Earth). Which best describes the spectrum seen by an earthbound observer? blueshifted hydrogen emission lines b blueshifted hydrogen absorption lines o) redshifted hydrogen emission lines d) redshifted hydrogen absorption lines e) a redshifted hydrogen continuum 4. The chemical composition of the Sun 3 billion years ago was different from what it is now in that it had Qmore hydrogen. - more helium. c) more nitrogen. d) molecular hydrogen. 5. The energy of a photon emitted by thermonuclear processes in the core of the Sun takes thousands or even millions of years to emerge from the surface because a) it is circling in the gravitational field of the Sun. b) it loses energy due to convection, conduction, and radiation. c) of the Sun's enormous radius. @it is absorbed and re-emitted countless times along the way. 6. Two stars have the same chemical composition, spectral type, and luminosity class, but one is 10 light years from the Earth and the other is 1000 light years from the Earth. The farther star appears to be a) 10 times fainter. b) 100 times fainter. @10,000 times fainter. d) 100,000,000 times fainter. e) the same brightness since the stars are identical. 7. Long—exposure color photographs of the night sky often show regions which glow red, such as the Eagle Nebula. This distinctive red color is caused by a, scattering of incoming starlight by dust grains in the nebula @he emission of red and infrared light by warm dust grains c. the ionization and recombination of hydrogen atoms d. the collective glow of many red giant stars in the region 8. Star A has a radius R and temperature T. At the same distance from Earth, star B has a radius 4R and temperature T/2. Which star appears to be brighter? s {b . ”‘53“ Both stars appear to have the same brightness. (1) Cannot tell from information given. 9. After the Sun's core hydrogen is depleted by nuclear fusion the core will consist primarily of a. carbon. b. deuterium. @elium. (1. oxygen. 10. The spectral-luminosity class of the star ocArae is B2 V and that 7: Herculis is K3 11. Using only this information, and not looking anything up in tables or diagrams, we know for sure: @ Only that ocArae is hotter than nHerculis b. Only that ocArae is cooler than querculis c. That oLArae has a lower luminosity than IrHerculis 11. If an interstellar cloud contracts to become a star, it is due to which force? a) electromagnetic b) nuclear @gravitational d) centrifugal 12. The solar corona has temperatures roughly the same as temperatures in the Sun's core, w ere nuclear fusion takes place. Fusion doesn't occur in the corona because '6) the density in the corona is too low. b) the corona has too many free electrons. c) atoms in the corona are mostly ionized. d) the corona has more heavy atoms than the core. e) Two of the above. 13. Consider two stars in constellation Pasta: Alpha Tortellini - bright in UV, dim in IR Beta Ziti - dim in UV, bright in IR There is little or no dust along the line of sight to Pasta. Which star is hotter? @Alpha Tortellini b) Beta Ziti c) Both are the same temperature. 14. The spectral curve on the graph below illustrates the energy output versus wavelength for an unknown star. Which of the absorption line spectra (a — (1) belongs to this unknown star? Wamleugth 15.When a star becomes a red giant it becomes much brighter because it is a) moving closer to us. b) losing its outer envelope. 0) fusing iron in its core. @increasing in size. 16. What is nuclear fusion? , a the process of turning matter into pure energy b. the process of splitting nuclei to produce energy the process of combining lightweight nuclei to make heavier nuclei d. a process that only occurs in bombs 17. Giant stars are more rare than main sequence stars because a) they do not form as often as main sequence stars. ) giant stars are unstable $the giant stage is very short compared to the main sequence stage. d) elements heavier than helium are relatively rare. 18. Suppose you measure the parallax of each star in the constellation Taurus (or any other cons llation you might choose). Which of the following is the most likely? a The stars all have the same parallax since we see them together in the same Constellation. b) The stars all have nearly the same parallax since they are moving together through space. 0) None of them has a measurable parallax since they are mostly within our own Solar System. (1) They may have significantly different parallaxes. e) We cannot measure their parallaxes since they are all moving toward our Sun. 19. A tuning fork diagram is shown to the right. Which of the labeled figures represents , 5 4 . we 0—.- 3 - {@[email protected]_Q3J 4 an Sa galaxy? a. l b. 2 939‘ .0 5 C2%. At which phase of its evolutionary life is a white dwarf star? a. just at main sequence phase b. early phases, soon after formation “\\ (yew late for small mass star, in dying phase post-supernova phase, the remnant of the explosion 21. Consider the information given below about the lifetime of three main sequence stars A, B, and C. a. Star A will be a main sequence star for 45,000 million years. b. Star B will be a main sequence star for 70 million years. 0. Star C will be a main sequence star for 2 million years. Which of the following is a true statement about these stars? a. Star A has the greatest mass. Lb} Star C has the greatest mass. c. Stars A, B and C all have approximately the same mass. (1. None of the above 22. How long will the Sun have to spent as a main sequence star when it finally begins to evolve toward the red giant phase? a. 1 million years b. 1010 years c. 1 billion years @45 million years 23 .An astronomer studying a galaxy finds that its spectrum shows only old, low mass, population stars, and photographs show little or no interstellar dust or gas. What kind of galaxy is this astronomer studying? A. an irregular galaxy B. a barred spiral galaxy C. an elliptical galaxy 24. Harlow Shapley first located the center of our galaxy in 1917 by: A. Redshift measurements on stars in the galactic plane and disk B. Measuring the positions of supernova explosions © Observing the distribution of globular clusters in the galactic halo. 25. Variable stars, such as Cepheid variables and RR Lyre, are used in what important measurement in astronomy? CEQSurface temperature measurement b. he keeping of accurate time c. Rotation speed of galaxies d. Distance measurement 26. Which of the following statements is not true for sunspots? Kggthey occur in regions of lower than average magnetic fields b. they increase and decrease in number, relatively regularly c. they are cooler than the surrounding photosphere of Sun 27. In which constellation in our sky is the center of our Milky Way galaxy located? a Ursa Major b. Hercules c. Sagittarius d. Lyra 28.Which of the following spectral classification of stars is in correct order of decreasing temperature? a. ABFGKMO b. KMGFABO C. OBAFGKM d. MKGFABO 29. Which of the following statements about an open cluster is true? @ All stars in the cluster are approximately the same age. b. All stars in the cluster are approximately the same color. 0. All stars in the cluster have approximately the same mass. d. All stars in the cluster will evolve similarly. c. There is an approximately equal number of all types of stars in the cluster. 30. The most basic difference between elliptical galaxies and spiral galaxies is that a. elliptical galaxies lack anything resembling the halo of a spiral galaxy. b. elliptical galaxies have a spheroidal component (of stars distributed ; spherically about the galactic center), and spiral galaxies do not. (Z) elliptical galaxies lack anything resembling the disk of a spiral galaxy. d. elliptical galaxies are very old and spiral galaxies are very young. Essay. Select two topics and answer with short, clear, correct statement. Points are assigned to each question. 1. Briefly describe how stars are classified according to their spectral characteristics. (temperature, chemical composition) 2. Describe briefly what method the scientists are using to calculate distance to the stars (hint: remember there are different distances, closer and farther away) 3. If the interior pressure of the sun were to become greater than the “ weight” of the outer regions, what would happen to the Sun? Explain. 4Draw a diagram showing the internal layers of the Sun and describe them briefly. 5 Sketch a drawing of Milky Way, first edge on and than as seen from above and describe the main characteristics each time. 6. Briefly summarize the stages of life for a high-mass star. 7. Where in the galaxy would you expect to find the following? Hot blue stars Massive star supernovae White dwarf supernovae Emission (ionization) nebulae 9.057s» I a 35;" ’5 “Ii 5 :“g'x it f: w M gag gag m1 P m “Ni 1 “i” if {I H r; ,3 {4; 2,1,535‘3‘5. l’ifiwaECAk “ta '3: " x): Khé, "ii/£353“ . 2.5“in m kiwi? 2 is: ' Mégigxgg " NW: 440% HA3 “HQ V2”; i419“ Cm: WMW ?a*v€~ (W (M 5’ Sflw “ifi‘éfii‘q *si W“ 4&5" 5:: « «3;; ENE: :bi‘fiéjr» i a r a: w , jib fifié‘; Bkfiflxfig ARM Phi? law ca law» a: . @fiitfifitfi a: gust! % i x a \ M? M“. in: 3 3 $VJ\G‘“%QI i VF in ‘ ‘ W 52 5:5) {I {9 (Rik ‘53:“ wt E’Vfi W {a 5R @ice‘l} ‘ Mg \ » Dian; with“ 5%? 5.3% On svw.mwa 53“ 929A “0‘. $3? P 3: i? {a Ev EQQM ”mama a {mfg jig“ i »_ FORMULA AND CONSTANT SHEET {DO NOT WRITE ON THIS SHEEZZ 1. d [m] = v [mlsec] x t [ sec] 2. Circumference = 27: r 3. Area of Circie = n r2 4. D = on d ‘ 206,265 P2 = a 3 Kepler’s law F = ma Newton 1“ law .991 7. F= Gm1m .1274 9-. Rp=a(1-e) ;'Ra= a(1+e) GM '10. Orbital speed v: T ZGM 11. Escape velocity 12:. R 12. E = mc:2 13.}. = c [Km/s] V 14. T = 2.9X1O.5an men’s Law Armax CONSTANTS C = 3x105 Kmlsee (speed of light) G = 6.67 x 10'11 m3 lkg set:2 gravitational 'const. 1Km= 1x103 meter ' 1AU =1. 5x108 km 1[ly]= 9. 46 x 10 ‘2 km= 6. 32 x 104AU 1pc= 3.261y=3.09x1013 km 1m= 109nm =101°A 1 Kg =2.2 lb . ‘1 lb = 0.454 kg Sun-Mercury= 0.4AU Saturn = 1OAU Venus= 0.7AU Uranus: ZOAU Mars: 1.5 AU Neptune: BOAU Jupiter: 5AU M em, = 5.97 x1024 kg M Sun = 1.98 x1030 kg R S... = 6.96 x10? km R MilkyWay =’50,000 ly 15. Temperature: 16. p ( density) = Mass / Volume F=9/5C+32° C=5l9 (F-32°) V: 4 n R3 K=C+273° 3 17. B1. /Bz-= (dz/d1)2 (Standard Candle. Method) 18. 8= L/ 47: R2 (brightness-flux) 19. d= -1/p parallax 20. R/Ro= (rorr)2 (L/Lo) / 21. m-M=5‘iogd-5 where To-Temp of Sun and L0 is Luminosity of Sun ...
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