Stars in Constellations - Physics and Astronomy - Past Exam, Exams of Physics

Download Stars in Constellations - Physics and Astronomy - Past Exam and more Exams Physics in PDF only on Docsity! 93/09(a) Semester 2, 2009 Page 1 of 11 ______________________________________________________________________________________________________________ _ THE UNIVERSITY OF SYDNEY SCHOOL OF PHYSICS PHYSICS 1500 - ASTRONOMY NOVEMBER 2009 Time allowed: TWO Hours TOTAL: 100 marks Section A Please use the answer sheet provided for this section. 20 multiple choice questions (1 mark each) Question 1 Why were the brighter planets not labelled as stars in the constellations, despite being known since antiquity? (a) The planets are brighter than the brightest stars in the constellations. (b) The planets move between constellations from one night to the next. (c) The planets move between constellations over weeks or months. (d) The planets are always moving faster than the stars across the sky. (e) Unlike the constellations, the planets return to the same parts of the sky from year to year. Question 2 Why don’t we see a solar eclipse every month? (a) The orbit of the Moon is tilted relative to the orbit of the Earth. (b) The Earth’s rotation axis is tilted relative to the orbit of the Moon. (c) The Moon takes slightly longer than a month to go around the Earth. (d) The orbit of the Moon is elliptical. (e) The orbit of the Earth is elliptical. 93/09(a) Semester 2, 2009 Page 2 of 11 ______________________________________________________________________________________________________________ _ Question 3 How are magnetic fields generated in the solar system? (a) Energetic particles colliding with an atmosphere (b) Deeply buried bar magnets (c) Convection within an iron-rich liquid (d) Currents in hydrogen under extreme pressure (e) Both (c) and (d) Question 4 Which one of the following objects is most like the planetesimals that formed in the proto-solar nebula? (a) Asteroid (b) Earth (c) Saturn (d) Venus (e) Sun Question 5 What is the name given to the disc-shaped cloud of icy bodies believed to extend from about 30 AU out to 50 AU or more. It is believed that short-period comets originate from this region. (a) Oort cloud (b) Widmanstätten cloud (c) Apollo-Amors (d) Kirkwood region (e) Kuiper belt Question 6 Where does our best information about the density of other planets come from? (a) Missions that have returned samples to Earth (b) The gravitational forces measured by orbiting spacecraft (c) Experiments carried out by astronauts (d) Observations by sensitive radio telescopes (e) Careful measurements of transits across the face of the Sun 93/09(a) Semester 2, 2009 Page 5 of 11 ______________________________________________________________________________________________________________ _ Question 15 Some properties of different stars in our Galaxy are listed below: I Metallicity roughly equal to the Sun’s II Typical location in the Galactic halo III Orbit lying close to the plane of the Milky Way IV Surrounded by gas and dust V Formation early in the history of the Galaxy Which of these properties are characteristic of Population II stars? (a) I and V (b) III, IV, and V (c) I, II, and IV (d) II and V (e) I and III Question 16 How do we know that the disc of the Milky Way is rotating? (a) There is a massive black hole at the Galactic Centre. (b) Much of the mass in the Milky Way is dark matter. (c) We see opposite Doppler shifts from gas clouds on either side of the Galactic Centre. (d) Nearby young star clusters and HII regions are located in a spiral arm pattern. (e) We can see Cepheids on the far side of the disc. Question 17 What is the origin of the hot spots in double-lobed radio galaxies? (a) Nuclear fusion of hydrogen (b) The interaction of high speed particles from the jets with the intergalactic medium (c) Location closest to the galaxy producing the lobes (d) Gravitational lensing of a single quasar (e) Light emitted direct from the accretion disk around a super-massive black hole 93/09(a) Semester 2, 2009 Page 6 of 11 ______________________________________________________________________________________________________________ _ Question 18 According to the current standard model for cosmology, large galaxies are formed by the merger of small systems. In this picture, the dwarf spheroidal galaxies (dSphs) are potentially a major building block of the Milky Way's halo. There is, however, a problem with this scenario. Why? (a) The amount of dark matter in the dSphs would significantly alter the structure of the Milky Way. (b) The chemical abundance of the dSphs differs from that of the Milky Way halo. (c) The dSphs mainly contain main sequence dwarf stars, which is not true for the Milky Way halo. (d) The process of galaxy merging has not been observed elsewhere in the universe. (e) There are no dSphs in the vicinity of the Milky Way. Question 19 What of the following is the main piece of evidence that the universe is expanding? (a) Redshifts are greater for more distant galaxies. (b) Light from distant quasars is sometimes bent by gravitational lensing. (c) The microwave background radiation has a blackbody spectrum. (d) There is not enough visible matter in clusters of galaxies to account for their hot x-ray gas (e) All the galaxies in our Local Group are all moving away from us. Question 20 In the early history of the universe, recombination refers to the time when the universe became transparent to photons. Which of the following correctly describes events at recombination? (a) Matter and antimatter annihilated to create a slight excess of matter (b) Protons and neutrons combined to produce deuterium and helium nuclei (c) Nuclei and electrons combined to produce neutral atoms (d) The first galaxies formed within clusters (e) The first stars formed within galaxies ------ This is the end of Section A. ------ 93/09(a) Semester 2, 2009 Page 7 of 11 ______________________________________________________________________________________________________________ _ Section B Please use the booklet provided for this section. THIS SECTION HAS EIGHT (8) QUESTIONS ANSWER ALL QUESTIONS (10 marks each) Question 1 Briefly describe ONE OBSERVATION supporting each of the following statements (two or three lines each): (a) Tidal forces are heating Io, the innermost Galilean satellite of Jupiter. (b) The surface of Mars was once warmer than it is today. (c) Most long period comets come from the Oort Cloud rather than the Kuiper Belt. (d) Neutrinos are produced by nuclear reactions in the core of the Sun. (e) Surface temperature of a star is related to the core temperature. (10 marks) Question 2 Briefly describe ONE OBSERVATION supporting each of the following statements (two or three lines each): (a) The interstellar medium is permeated by dust particles with a size roughly comparable to the wavelength of visible light. (b) Recent star formation occurs in the spiral arms of galaxies. (c) There is a massive black hole at the centre of the Milky Way. (d) Quasars are relatively small objects, much smaller than their host galaxy. (e) Dark matter cannot be baryonic. (10 marks) 93/09(a) Semester 2, 2009 Page 10 of 11 ______________________________________________________________________________________________________________ _ Question 7 The graph below shows a plot of the relative abundance of elements found in the solar system (note the logarithimic vertical scale). (a) Why are Hydrogen and Helium by far the most abundant elements in the solar system? (b) Why is Iron (Fe) far more abundant than all the heavier elements, and even more abundant than many of the lighter elements? (c) Much of the diagram exhibits an up-down zigzag pattern with alternate atomic number. What is the origin of this pattern? (d) The three most important nuclear reactions in stars are: i) proton-proton chain ii) CNO cycle iii) triple-alpha process For each reaction, describe the types of stars in which it is the dominant reaction. (e) Briefly describe why, in general, heavier elements require higher core temperatures to sustain fusion reactions. (10 marks) 93/09(a) Semester 2, 2009 Page 11 of 11 ______________________________________________________________________________________________________________ _ Question 8 (a) Briefly outline three key observations supporting the Big Bang model of the universe. (b) In a few lines, explain what occurred in the Inflationary Era in the evolution of the universe. (c) Inflation explains two key problems in the Big Bang model. Outline these problems and explain how inflation solves them. (d) Briefly describe each of the significant components of the energy density of the universe as it is understood today, including their approximate percentage contributions. (10 marks) ------ This is the end of your questions. ------