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Astronomy A105 Midterm 2 Spring 2007 ______________________________________ Name Multiple Choice (3 points each): Please circle your answers as they will be your only record of the answers you have given on the test. Please then mark the answer in the appropriate bubble on the scan sheet. Be sure to include your name. Use only a #2 pencil. If your pencil breaks, or you do not have one, a pencil will be provided at the front of the room. There are 25 multiple choice questions. 1) When we examine the rotation curve (shown above) for our galaxy we notice that the orbital velocities increase as you go to the outmost parts of our galaxy. From that fact, we know that 90% of our galaxy’s mass is in what form? • A) Hydrogen • B) stars • C) dust • D) dark matter 2) How long does it take our sun to orbit our galaxy? • A) 25 million years • B) 250 million years • C) 2.5 billion years • D) our sun does not orbit our galaxy 3) What type of galaxy do we live in? • A) unbarred spiral • B) barred spiral • C) elliptical • D) irregular 4) What is a bubble? • A) a region of space with less gas • B) a region of space with more gas • C) another term for a star forming region • D) a region that is completely empty 5) If a bubble breaks through the disc of our galaxy what happens? • A) the bubble stops expanding • B) a pressure blow out • C) the bubble becomes a star forming region • D) the bubble forms a spiral arm 6) What determines the volume of space that a hot phase region can expand into? • A) velocity of the hot phase • B) temperature of the hot phase • C) pressure of the hot phase • D) Trick! The hot phase contracts. 7) The B-V value of the sun is 0.68 as viewed from earth. What is the B-V value for the sun from Jupiter (5 times further away from the sun than the earth)? • A) 0.68 • B) 3.4 • C) 5.68 • D) 17 8) The B-V value of the sun is 0.68 as viewed from earth. What would the V value for the sun be if it were in the Pleiades cluster as diagramed above? • A) V = 5 • B) V = 8 • C) V = 11 • D) V = 16 9) What determines the resolution of a telescope? • A) diameter • B) light collected • C) magnification • D) all of these 10) If a neutron star accretes matter from a companion star, how does the spin change? • A) spins faster • B) spins slower • C) spin unchanged • D) stops spinning 11) What are pulsars? • A) rapidly spinning neutron stars • B) rapidly spinning black holes • C) stars that change temperature rapidly • D) stars that change size rapidly 12) Where does the energy that pulsars emit come from? • A) heat • B) fusion • C) gravity • D) spin 13) If we know a star’s apparent and absolute brightnesses (or magnitudes) then what value can we calculate? • A) age of the star • B) distance to the star • C) temperature of the star • D) we can calculate all of these 14) Absolute Magnitude is a measure of: • A) a star’s brightness as viewed from the earth • B) a star’s brightness as viewed from 93 million miles away • C) a star’s brightness as viewed from 10 parsecs away • D) the temperature of a star 15) Apparent Magnitude is a measure of: • A) a star’s brightness as viewed from the earth • B) a star’s brightness as viewed from 93 million miles away • C) a star’s brightness as viewed from 10 parsecs away • D) the temperature of a star 16) Which of the following does NOT affect how much energy an object radiates? • A) radius of the object • B) temperature of the object • C) distance to the object • D) all of these affect how much energy the object radiates 17) What is NOT true of stars in a cluster? • A) they are about the same distance away • B) they are about the same age • C) they are about the same mass • D) all of these are true 18) How do we find the distance to a cluster? • A) by finding the color of the turn off point • B) by finding the brightness of the turn off point • C) by finding the color of the sun if it were in the cluster and comparing that to its actual color • D) by finding the brightness of the sun if it were in the cluster and comparing that to its actual brightness 19) What is the best way to find the age of a cluster? • A) by finding the color of the turn off point • B) by finding the brightness of the turn off point • C) by finding the color of the sun if it were in the cluster and comparing that to its actual color • D) by finding the brightness of the sun if it were in the cluster and comparing that to its actual brightness The diagram above will be used for questions 20 and 21. 20) For the HR diagram shown, if stars A and B are the same distance from earth which has a higher temperature (ignore absorption)? • A) A • B) B • C) they have the same temperature • D) you cannot tell from this diagram 21) For the HR diagram shown, if stars A and B are the same distance from earth which is brighter (ignore absorption)? • A) A • B) B • C) they have the same brightness • D) you cannot tell from this diagram 22) Where do you normally find spiral galaxies? • A) in the cores of giant galaxy clusters • B) on their own with a few satellite galaxies • C) in orbit around a larger galaxy • D) everywhere 23) Where are you most likely to find giant elliptical galaxies? • A) in the cores of giant galaxy clusters • B) on their own with a few satellite galaxies • C) in orbit around a larger galaxy • D) everywhere 24) What type of galaxy do the smallest galaxies fall under? • A) spiral galaxies • B) elliptical galaxies • C) irregular galaxies • D) all galaxy types are the same size 25) What type of galaxy do the largest galaxies fall under? • A) spiral galaxies • B) elliptical galaxies • C) irregular galaxies • D) all galaxy types are the same size 26 Please mark A A) mark A B) mark A C) mark A D) mark A SHORT ANSWER QUESTIONS: Each question is worth 15 points. Be sure to answer all parts of all questions fully (I can’t give points if you don’t answer). Please note that there are 5 short answer questions! Please do all 5. 1) What are the 3 components of our galaxy? Which parts of our galaxy do you find Population I stars? Which parts do you find Population II stars? What are the differences between Population I and Population II stars? 2) What are the 3 phases of the Interstellar Medium (ISM)? Rank the phases by temperature and by density (specify which are highest and lowest). How does each phase play a role in the “circle of life”? 3) Why is it difficult to observe the center of our galaxy in the optical? What type of light is the best type of light to use to observe the center of our galaxy? Why is this type of light the best? 4) For the above image circle the globular cluster. How did you know that was the globular cluster (even if you guess why did you guess that – what about it said to you that it might be the globular cluster)? What are the dark spots on the image? 5) For the image above circle the 3 star groups. For each cluster label them as either globular cluster, open cluster, or galaxy. If it is a galaxy, what type of galaxy is it? What do the colors of the star groups tell you about each group (name 2 things – but they sort of relate to each other – i.e. what does the first thing also tell you?)? BONUS: What are the names of the star groups (i.e. if galaxy – name of galaxy, if star cluster, name of star cluster)?