Introduction to Astronomy and Cosmology

Transcription

1 Introduction to Astronomy and Cosmology Ian Morison University of Manchester, UK A John Wiley and Sons, Ltd., Publication

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3 Introduction to Astronomy and Cosmology

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5 Introduction to Astronomy and Cosmology Ian Morison University of Manchester, UK A John Wiley and Sons, Ltd., Publication

6 This edition first published John Wiley & Sons Registered office John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of fitness for a particular purpose. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for every situation. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of experimental reagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising herefrom. Library of Congress Cataloging-in-Publication Data Morison, Ian, 1943 Introduction to astronomy and cosmology / Ian Morison. p. cm. Includes bibliographical references and index. ISBN (cloth) ISBN (pbk. : alk.paper) 1. Astronomy Textbooks. 2. Cosmology Textbooks. I. Title. QB43.3.M dc A catalogue record for this book is available from the British Library. Set in 8/10 pt Photina by Integra Software Services Pvt. Ltd. Pondicherry, India. Printed and bound in Spain by Grafos SA, Barcelona

7 To the memory of my father, Archibald, who inspired my love of astronomy, to Bernard Lovell who made it possible for me to pursue that love and to my wife, Judy, with love.

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9 Contents Preface Biography xv xvii Chapter 1: Astronomy, an Observational Science Introduction Galileo Galilei s proof of the Copernican theory of the solar system The celestial sphere and stellar magnitudes The constellations Stellar magnitudes Apparent magnitudes Magnitude calculations The celestial coordinate system Precession Time Local solar time Greenwich mean time The equation of time Universal time Sidereal time An absolute time standard cosmic time A second major observational triumph: the laws of planetary motion Tycho Brahe s observations of the heavens Johannes Kepler joins Tycho Brahe The laws of planetary motion Measuring the astronomical unit Isaac Newton and his Universal Law of Gravity Derivation of Kepler s third law Experimental measurements of G, the Universal constant of gravitation Gravity today: Einstein s special and general theories of relativity Conclusion Questions 36 vii

10 viii Contents Chapter 2: Our Solar System 1 The Sun The formation of the solar system The Sun Overall properties of the Sun The Sun s total energy output Black body radiation and the sun s surface temperature The Fraunhofer lines in the solar spectrum and the composition of the sun Nuclear fusion The proton proton cycle The solar neutrino problem The solar neutrino problem is solved The solar atmosphere: photosphere, chromosphere and corona Coronium The solar wind The sun s magnetic field and the sunspot cycle Sunspots The sunspot cycle Prominences, flares and the interaction of the solar wind with the earth s atmosphere The aurora Solar eclipses Two significant solar eclipses The Shapiro delay Questions 72 Chapter 3: Our Solar System 2 The Planets What is a planet? Planetary orbits Orbital inclination Planetary properties Planetary masses Planetary densities Rotation periods Planetary temperatures Global warming Albedo 83

11 Contents ix 3.4 Planetary atmospheres Secondary atmospheres The evolution of the earth s atmosphere The planets of the solar system Mercury Venus The Earth The moon Mars Ceres and the minor planets Jupiter Saturn Uranus Neptune Pluto Eris Comets Halley s comet Cometary nuclei Questions 132 Chapter 4: Extra-solar Planets The radial velocity (Doppler wobble) method of planetary detection Pulsar planets The discovery of the first planet around a sun-like star Planetary transits Gravitational microlensing Astrometry Discovery space Selection effects and the likelihood of finding solar systems like ours Questions 151 Chapter 5: Observing the Universe Thinking about optics in terms of waves rather than rays The parabolic mirror Imaging with a thin lens The achromatic doublet 159

12 x Contents 5.2 The human eye The use of a telescope or pair of binoculars to see fainter objects Using a telescope to see more detail in an image An interesting worked example of the effects of diffraction The effect of diffraction on the resolution of a telescope The magnification of a telescope Image contrast The classic Newtonian telescope The Cassegrain telescope Catadioptric telescopes The Schmidt camera The Schmidt Cassegrain telescope The Maksutov Cassegrain telescope Active and adaptive optics Active optics Adaptive optics Some significant optical telescopes Gemini North and South telescopes The Keck telescopes The South Africa Large Telescope (SALT) The Very Large Telescope (VLT) The Hubble Space Telescope (HST) The future of optical astronomy Radio telescopes The feed and low noise amplifier system Radio receivers Telescope designs Large fixed dishes Telescope arrays Very Long Baseline Interferometry (VLBI) The future of radio astronomy Observing in other wavebands Infrared Submillimetre wavelengths The Spitzer space telescope Ultraviolet, X-ray and gamma-ray observatories 195

13 Contents xi 5.14 Observing the universe without using electromagnetic radiation Cosmic rays Gravitational waves Questions 202 Chapter 6: The Properties of Stars Stellar luminosity Stellar distances The parsec Proper motion Hipparcos and GAIA The absolute magnitude scale The standard formula to derive absolute magnitudes Colour and surface temperature Stellar photometry Stellar spectra The hydrogen spectrum Spectral types Spectroscopic parallax The Hertzsprung Russell Diagram The main sequence The giant region The white dwarf region Pressure broadening The size of stars Direct measurement Using binary star systems to calculate stellar sizes Using the Stephan Boltzman law to estimate stellar sizes The masses and densities of stars The stellar mass luminosity relationship Stellar lifetimes Questions 230

14 xii Contents Chapter 7: Stellar Evolution The Life and Death of Stars Low mass stars: solar masses Mid mass stars: solar masses Moving up the main sequence The triple alpha process The helium flash Variable stars Planetary nebula White dwarfs The discovery of white dwarfs The future of white dwarfs Black dwarfs The evolution of a sun-like star Evolution in close binary systems the Algol paradox High mass stars in the range 8 solar masses Type II supernova The Crab Nebula Supernova 1987A Neutron stars and black holes The discovery of pulsars What can pulsars tell us about the universe? Pulsars as tests for general relativity Black holes The detection of stellar mass black holes Black holes are not entirely black Questions 262 Chapter 8: Galaxies and the Large Scale Structure of the Universe The Milky Way Open star clusters Globular clusters The interstellar medium and emission nebulae Size, shape and structure of the Milky Way Observations of the hydrogen line A super-massive black hole at the heart of our galaxy 275

15 Contents xiii 8.2 Other galaxies Elliptical galaxies Spiral galaxies Evidence for an unseen component in spiral galaxies dark matter Weighing a galaxy Irregular galaxies The Hubble classification of galaxies The universe The cosmic distance scale Using Supernova 1987A to measure the distance of the Large Magellanic Cloud The Cepheid variable distance scale Starburst galaxies Active galaxies Groups and clusters of galaxies Superclusters The structure of the universe Questions 298 Chapter 9: Cosmology the Origin and Evolution of the Universe Einstein s blunder? Big Bang models of the universe The blueshifts and redshifts observed in the spectra of galaxies The expansion of the universe A problem with age The steady state model of the universe Big Bang or Steady State? The cosmic microwave background The discovery of the cosmic microwave background Inflation The Big Bang and the formation of the primeval elements The ripples in the Cosmic Microwave Background How dark matter affects the cosmic microwave background The hidden universe: dark matter and dark energy Evidence for dark matter How much non-baryonic dark matter is there? What is dark matter? 319