Table Of ContentAstronomy Explained
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Astronomy
Explained
Gerald North
With 161 Figures
Springer
Gerald North BSc
9 Camperdown Street, Sidley, Bexhill-on-Sea,
East Sussex TN39 5BE, UK
Cover illustrations: Front cover image of Jupiter was taken with the Hubble Space
Telescope's Planetary Camera and shows eight impact sites from the disintegrated
comet Shoemaker-Levy 9 in July 1994 (courtesy Hubble Space Telescope Comet Team
and NASA). Back cover photograph of Villafranca (courtesy ESA).
ISBN-13: 978-3-540-76136-5 e-ISBN-13: 978-1-4471-0901-3
DOl: 10.1007/978-1-4471-0901-3
British Library Cataloguing in Publication Data
North, Gerald
Astronomy explained
l.Astronomy 2.Space sciences 3.Astronomy - Problems,
exercises, etc. 4.Space sciences - Problems, exercises, etc.
I.Title
520
ISBN 3540761365
Library of Congress Cataloging-in-Publication Data
North, Gerald, 1958-
Astronomy explained 1 Gerald North.
p. cm.
Includes index.
1. Astronomy. I. Title.
QB45.N69 1997 97-3761
520-DC21 CIP
Apart from any fair dealing for the purposes of research or private study, or criticism
or review, as permitted under the Copyright, Designs and Patents Act 1988, this publi
cation may only be reproduced, stored or transmitted, in any form or by any means,
with the prior permission in writing of the publishers, or in the case of reprographic
reproduction in accordance with the terms of licences issued by the Copyright
Licensing Agency. Enquiries concerning reproduction outside those terms should be
sent to the publishers.
© Springer-Verlag London Limited 1997
Softcover reprint of the hardcover 18t edition 1997
The use of registered names, trademarks, etc. in this publication does not imply, even
in the absence of a specific statement, that such names are exempt from the relevant
laws and regulations and therefore free for general use.
The publisher makes no representation, express or implied, with regard to the accuracy
of the information contained in this book and cannot accept any legal responsibility or
liability for any errors or omissions that may be made.
Typeset by EXPO Holdings, Malaysia
58/3830-543210 Printed on acid-free paper
Preface
Every year large numbers of people take up the study of astronomy,
mostly at the amateur level. There are plenty of elementary books on
the market, full of colourful photographs but lacking in proper expla
nations of how and why things are as they are. Many people eventu
ally wish to go beyond the coffee-table book stage and study this
fascinating subject in greater depth. This book is written for them.
In addition, many people sit for public examinations in this subject
each year. This book is also intended to be of use to them. I have been
careful to cover all the topics in the syllabus of the GCSE astronomy
course and to provide a selection of sample questions at the end of
each chapter. Although these questions are intended for prospective
examination candidates, the more casual reader might wish to try
some of them just for fun! Astronomy is also a component part of
many college and schools subjects - ranging from general studies
options to whole sections of physics and geology courses.
Much material is available at both the elementary and advanced
(university) levels in this subject but little bridging the gap.
Nevertheless, today's amateur astronomers are becoming very much
more sophisticated in their approach than was the case just a few
years ago. In this book I have tried to give a comprehensive treatment
of the subject but in more depth than is usually found in elementary
works. Some mathematics is included, though it is only at a basic
level. Much of Chapter 1 covers material specified in the GCSE exam
ination syllabus and can be glossed over by the casual reader. The
same is true for the parts of Chapter 2 that are concerned with calcu
lations on time. I hope that you find this book interesting. If you are
sitting for an examination in, or involving, astronomy I wish you the
very best ofluck and I hope that this book will help you.
Gerald North
1997
v
AcknoYlledgernents
I would like to thank the Director and staff of the Royal Observ
atories, Cambridge (formerly the Royal Greenwich Observatory,
Herstmonceux), and the Jet Propulsion Laboratory, Pasadena, for
permission to use the photographs included in this book.
In addition, my friends Martin Mobberley and Eric Strach have
very kindly let me use some of their most excellent photographs.
I would also like extend my thanks to Mr John Winckler and his
staff at Macmillan Press Ltd., for their sterling work in the publishing
of the first edition of this book and to Mr John Watson and his staff at
Springer-Verlag for their excellent work in the publication of this new
and enlarged edition.
I am most grateful to all of the above.
G.N.
vii
Contents
List of Figures . . . . . . xvii
1 The Celestial Sphere
1.1 The Concept of the Celestial Sphere 1
1.2 Latitude and Longitude ..... . 2
1.3 Declination and Right Ascension . 3
1.4 The Altitude of the Celestial Equator and Poles 7
1.5 The Starry Vault . . . . . . . . . . . . . . . 10
1.6 A Better Definition of Right Ascension ... 11
1.7 To Calculate the Maximum Altitude of a Star 12
1.8 Circumpolar Stars . . 14
1.9 Stars that Never Rise 15
1.10 Azimuth ..... 15
1.11 The Earth in Space . . 16
1.12 The Seasons ..... 19
1.13 The Moon and the Celestial Sphere 19
1.14 The Solar System and the Celestial Sphere 20
1.15 Stellar Motions 20
1.16 Precession 21
Questions ...... . 21
2 The Earth and Time
2.1 The Shape and Size ofthe Earth 24
2.2 The Earth in the Solar System . 25
2.3 The Structure of the Earth . . . 26
2.4 The Surface Conditions on the Earth 28
2.5 The Atmosphere of the Earth . 29
2.6 The Ionosphere ....... . 30
2.7 The Terrestrial Magnetosphere 31
2.8 The Van Allen Radiation Zones 32
2.9 The Aurorae . . . . . . . . . . 33
2.10 The Need for Time Measurement 34
2.11 Calendars............ 35
ix
x Contents
2.12 The Solar Day . 35
2.13 Universal Time 36
2.14 Time Zones 37
2.15 Hour Angle 37
2.16 The Sidereal Day 38
2.17 A Fundamental Equation 38
2.18 The Measurement of Time 40
Questions 41
3 The Telescope
3.1 Chromatic Aberration . . . . . . 44
3.2 The Achromatic Objective . . . . 46
3.3 Light Grasp and Resolving power 47
3.4 Eyepieces and Magnification 49
3.5 The Effects of Magnification on the Image 50
3.6 The Limitations Caused by the Earth's Atmosphere 51
3.7 The Reflecting Telescope 52
3.8 Spherical Aberration ..... . 55
3.9 The Development of the Reflector 56
3.10 Telescope Mountings 58
3.11 The Schmidt Camera 61
Questions 62
4 Modern Developments in Instrumentation
4.1 The Photographic Plate 64
4.2 The Photomultiplier . . . 64
4.3 Electronic Imaging 65
4.4 Getting More Resolution 67
4.5 The Latest Generation of Optical Telescopes 69
4.6 The Radio Telescope ..... . 72
4.7 Astronomy at Other Wavelengths 74
4.8 Astronomy Above the Ground 74
Questions ............. . 75
5 Gravitation
5.1 Kepler's Laws of Planetary Motion 77
5.2 Newton's Law of Gravitation 79
5.3 Circular Motion . . . . . . . . . . 80
5.4 Mathematical Derivation of Kepler's Third law 82
5.5 Two-Body Orbiting Systems ........ . 83
5.6 The Tides ................. . 83
5.7 The Measurement ofthe Astronomical Unit 84
5.8 The Earth's Gravitational Field . 86
5.9 The Acceleration Due to Gravity 87
5.10 Rockets and Satellites 88
Questions 91
Contents xi
6 TheMoon
6.1 The Nature and Origin of the Moon 92
6.2 The Orbit and Phases of the Moon 93
6.3 Lunar Eclipses 94
6.4 The Saros ............ . 96
6.5 Libration . . . . . . . . . . . . . . 96
6.6 The Measurement of the Moon's Distance 98
6.7 The Selenographers ........ . 99
6.8 Lunar Probes and Man on the Moon 100
6.9 The Moon's Appearance . . . . . . . 102
6.10 Surface Conditions ........ . 106
6.11 The Structure and Evolution of the Moon 107
6.12 Transient Lunar Phenomena 108
Questions ................... . 109
7 The Inferior Planets
7.1 Stellar and Planetary Brightnesses 110
7.2 The Orbit and Phases of Mercury 111
7.3 Mercury's Telescopic Appearance 111
7.4 The Rotation Rate of Mercury .. 113
7.5 Mariner 10 ........... . 115
7.6 Comparison Between Mercury and the Moon 116
7.7 The Caloris Basin ......... . 117
7.8 The Surface Conditions on Mercury 117
7.9 The Orbit and Phases of Venus 117
7.10 Venus's Telescopic Appearance 118
7.11 The Size and Nature of Venus 119
7.12 Spacecraft to Venus ..... . 119
7.13 Venus - a Volcanic Planet? 121
7.14 Magellan and Yet More Mysteries 121
7.15 The Earth and Venus - Worlds Apart 122
7.16 The Greenhouse Effect - a Difference in Evolution 123
Questions 124
8 The Planet Mars
8.1 Oppositions ................ . 125
8.2 The Path of Mars Across the Celestial Sphere 126
8.3 The Telescopic Appearance of Mars 127
8.4 The Martian Atmosphere . 130
8.5 The Canals of Mars 131
8.6 Early Space Probes to Mars 132
8.7 Later Space Probes to Mars 133
8.8 Vikings to Mars .. 134
8.9 Life on Mars? 136
8.10 Phobos and Deimos 138
Questions 138
xii Contents
9 The Planet Jupiter
9.1 The Telescopic Appearance ofJupiter 140
9.2 Transient Features . .. ..... . 141
9.3 The Great Red Spot ..... . 142
904 Pioneers 10 and 11 ... .............. . 143
9.5 The Voyager Missions. . .... . 144
9.6 Collision with a Comet ..... . 145
9.7 Galileo Enters the Jovian Atmosphere 146
9.8 The Structure ofJupiter 147
9.9 Jupiter's Magnetosphere 147
9.10 Radiation Belts 148
9.11 Radio Emissions 148
9.12 The Satellites 148
9.13 10 149
9.14 Europa .. 151
9.15 Ganymede 151
9.16 Callisto 151
9.17 The Rings ofJupiter 152
Questions ..... . 152
10 The Planet Saturn
10.1 The Telescopic Appearance of Saturn 153
10.2 Spacecraft to Saturn .... 155
10.3 The Atmosphere of Saturn 156
lOA The Structure of Saturn 157
10.5 Saturn's Magnetosphere .. 157
10.6 The Rings of Saturn .... 158
10.7 Voyager - a Detailed Look at the Rings 159
10.8 The Formation of Planetary Rings 161
10.9 The Satellites of Saturn 162
10.10 Titan 164
Questions 165
11 The Twilight Zone of the Solar System
11.1 The Planet Uranus .. . 166
11.2 Voyager to Uranus .. . 168
11.3 The Satellites of Uranus 170
1104 The Planet Neptune .. 171
11.5 Voyager at Neptune .. 172
11.6 Neptune's Rings and Satellites 174
11.7 The Planet Pluto 174
Questions 176
12 The Debris of the Solar System
12.1 The Formation of the Solar System 177
12.2 Planetary Cratering 179
12.3 Bode's Law ..... 180
1204 The Celestial Police 180
