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Space And Astronomy An Illustrated Guide To Science Science Visual Resources Diagram Group

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Space And Astronomy An Illustrated Guide To Science Science Visual Resources Diagram Group
Space And Astronomy An Illustrated Guide To Science Science Visual Resources Diagram Group
SPACE AND ASTRONOMY SCIENCE VISUAL RESOURCES An Illustrated Guide to Science The Diagram Group
Space and Astronomy: An Illustrated Guide to Science Copyright © 2006 The Diagram Group Editorial: Tim Furniss, Gordon Lee, Jamie Stokes Design: Anthony Atherton, Richard Hummerstone, Lee Lawrence, Trevor Mason, Roger Pring, Phil Richardson Illustration: Trevor Mason, Peter Wilkinson Picture research: Neil McKenna Indexer: Martin Hargreaves All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Chelsea House An imprint of Infobase Publishing 132 West 31st Street New York NY 10001 For Library of Congress Cataloging-in-Publication data, please contact the publisher. ISBN 0-8160-6168-8 Chelsea House books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at 212/967-8800 or 800/322-8755. You can find Chelsea House on the World Wide Web at http://www.chelseahouse.com Printed in China CP Diagram 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper.
Introduction Space and Astronomy is one of eight volumes of the Science Visual Resources set. It contains eight sections, a comprehensive glossary, a Web site guide, and an index. Space and Astronomy is a learning tool for students and teachers. Full-color diagrams, graphs, charts, and maps on every page illustrate the essential elements of the subject, while parallel text provides key definitions and step-by-step explanations. The Universe provides an overview of the physical dimensions of space and current theories concerning its origin and eventual fate. This section also defines and illustrates the main classes of objects, from black holes to binary stars, that populate the known universe. The Sun’s Family examines our solar system and defines the various classes of celestial bodies that it includes. There are detailed comparisons of all nine planets as well as information about asteroids, meteoroids, planetary moons, and the Sun itself. Astronomy is concerned with the human effort to observe and understand objects beyond Earth from the earliest civilizations to the present day. It describes the different methods of astronomy that are used to examine the universe across the entire electromagnetic spectrum. Space Travel is an overview of the practical and theoretical challenges of getting into space and traveling through it. All aspects of space travel are covered, from the basics of celestial mechanics to the relative pros and cons of different types of propulsion. Uncrewed Exploration is a history of the exploration of space by uncrewed spacecraft. Crewed Exploration is a history of manned expeditions in space, from Yuri Gagarin to the contemporary crews of the International Space Station. The Space Shuttle and Using Space are concerned with the economic and scientific importance of space today. The many classes of satellite that provide the world with telecommunications and vital data are examined here.
Contents 8 Size and scale 9 Distances 10 Beginnings of the universe 11 Endings of the universe 12 Bright stars 13 Close stars 14 Star pairs 15 Variable stars 16 Exoplanets 17 Stellar evolution 18 Stellar beginnings 19 Stellar birth 20 Regular star death 21 Large star death 22 Giant star death 23 Neutron stars 24 Black holes 25 Quasars 26 The Milky Way 27 Galaxy types 28 Galaxy groups 29 Hubble’s law 1 THE UNIVERSE 30 Beginnings of the solar system 31 Sizes 32 Distances 33 Temperatures 34 Orbits 35 Moons 36 Gravities 37 Planet summaries 38 Sunspots and flares 39 Solar wind 40 Mercury 41 Venus 42 Earth 43 The Moon 44 Earth’s tides 45 Lunar phases 46 Solar eclipses 47 Lunar eclipses 48 Lunar features 49 Meteoroids 50 Mars 51 Jupiter 52 Jupiter’s moons 53 Asteroids 54 Near Earth Objects 55 Saturn 56 Saturn’s rings 57 Uranus 58 Neptune 59 Pluto 60 Comets 61 Trans-Neptunian objects 62 Kuiper belt objects 63 Oort cloud objects 2 THE SUN’S FAMILY
64 Sky watching 65 Early astronomy 66 First astronomers 67 Renaissance astronomers 68 Electromagnetic spectrum 69 First telescopes 70 18th-century telescopes 71 Radio astronomy 72 Modern telescopes 73 Infrared astronomy 74 Ultraviolet astronomy 75 X-ray astronomy 76 Gamma ray astronomy 77 Cosmic ray astronomy 78 Sky map 79 Constellations 3 ASTRONOMY 80 Getting into orbit 81 Changing orbits 82 Getting to planets 83 Orbital inclination 84 Common Earth orbits 85 Uncommon Earth orbits 86 How rockets work 87 Liquid rocket fuel 88 Solid rocket fuel 89 Rocket stages 90 Rocket steering 91 Ion engines 92 Meeting in space 93 Walking in space 94 Returning to Earth 95 Space junk 4 SPACE TRAVEL 96 Early rockets 97 First western rockets 98 First eastern rockets 99 First military rockets 100 Sputnik 1 101 Sputnik 2 and 3 102 Explorer 1 103 Vanguard program 104 Explorer program 105 Discoverer and Corona 106 Telstar 1 107 Exploring the Sun 108 Exploring Mercury 109 Exploring Venus 110 Landing on Venus 111 Exploring the Moon 5 UNCREWED EXPLORATION
112 Landing on the Moon 113 Mars: early exploration 114 Mars: recent exploration 115 Mars: first landings 116 Mars: recent landings 117 Jupiter: early exploration 118 Jupiter: recent exploration 119 Saturn: early exploration 120 Saturn: recent exploration 121 Exploring Uranus and Neptune 122 Exploring asteroids 123 Exploring comets 124 Vostok 125 Mercury 126 Gemini 127 Voskhod 128 Soyuz 129 Apollo: overview 130 Apollo: getting there 131 Apollo: landing 132 Apollo: getting back 133 Apollo: Command Module 134 Apollo: Service Module 135 Apollo: Lunar Module 136 Apollo: Lunar Roving Vehicle 137 Apollo: Saturn V 138 Apollo: launch site 139 Apollo: landing sites 140 Apollo: science 141 Salyut 1–5 142 Salyut 6 and 7 143 Skylab 144 Mir 145 Mir parts 146 Shuttle-Mir 147 International Space Station 148 International Space Station: U.S./Russia 149 International Space Station: other countries 150 Shenzhou 151 Space travelers 6 CREWED EXPLORATION
198 Key words 205 Internet resources 207 Index APPENDIXES 152 Space Shuttle 153 Orbiter 154 Launch engines 155 Fuel tank 156 Flight path 157 Emergencies 158 Crew quarters 159 Space walking 160 Maneuvering 161 Heat protection 162 Hygiene 163 Robotic arm 164 Cargo 165 Cockpit flight controls 166 Food 167 Living 168 Working 169 Launching satellites 170 Launch 171 Landing 7 THE SPACE SHUTTLE 172 Television satellites 173 Multimedia satellites 174 Mobile communications satellites 175 Navigation satellites 176 Earth-watching satellites 177 Weather satellites 178 Environmental satellites 179 Atmospheric satellites 180 Radiation satellites 181 Data satellites 182 Earth observation satellites 183 Optical spy satellites 184 Radar spy satellites 185 Radio spy satellites 186 Early-warning satellites 187 Research satellites 188 Sun-watching satellites 189 Microgravity satellites 190 Radio astronomy 191 Infrared astronomy 192 Ultraviolet astronomy 193 X-ray astronomy 194 Gamma ray astronomy 195 Cosmic Background Explorer 196 Hubble Space Telescope 197 Launch totals 8 USING SPACE
Size and scale ? 1,500,000 ly 150 million ly 15 billion ly 1,500 billion ly 0.015 ly 1.5 ly 150 ly 15,000 ly 3 4 7 8 5 6 1 2 THE UNIVERSE The universe ● The universe is the entirety of all matter, energy, and phenomena. ● The origins and ultimate fate of the universe are uncertain. Cubes of space ● Each cube has sides 100 times longer than the preceding cube. ● Each cube has a volume one million times greater than the preceding cube. 0.015 light years The solar system. 1.5 light years The Oort cloud. 150 light years The nearest stars to the Sun. 15,000 light years Part of a spiral arm of the Milky Way. 1,500,000 light years The Local Group of galaxies. 150 million light years The Local Supercluster of galaxies. 15 billion light years All known galaxies. 1,500 billion light years Unknown. galaxy galaxy group galaxy supercluster Local Group Local Supercluster Milky Way Oort cloud solar system star Key words 8 1 2 3 4 5 6 7 8 © Diagram Visual Information Ltd.
Defining a parsec ● Earth (a) orbits the Sun (b) at a distance of 1 au. ● Over a period of about three months, Earth moves from position 1 to position 2. ● A nearby star (c) will change position against the background of more distant stars when observed from Earth at position 1 and then position 2. ● This change in angular position (p) is known as parallax. ● When a star’s parallax is exactly 1 arc second (1/3600 of a degree) that star is exactly one parsec distant from Earth. ● The distance in parsecs of any star that is close enough to have an observable parallax can be calculated from this relationship. THE UNIVERSE Measuring distances ● Astronomical distances are too large to be usefully measured in miles or kilometers. ● Astronomers use much larger units of measurement. Astronomical unit (au) ● An astronomical unit (au) is the mean distance between Earth and the Sun. ● It is used to describe distances within solar systems. Light year (ly) ● A light year (ly) is the distance traveled by light in a vacuum in one year. ● It is used to describe the distances between stars or the dimensions of galaxies. ● Terms such as light second, light day, or light month are also used to denote distances traveled by light in other time spans. Parsec (pc) ● Parsec (pc) is an abbreviation of “parallax second.” ● This denotes the distance at which a baseline of 1 au subtends an angle of 1 arc second. ● It is used to describe distances between galaxies. ● The terms kiloparsec (kpc) and megaparsec (Mpc) are also used to denote distances of 1,000 parsecs and one million parsecs respectively. Distances Astronomical distances 1 au 93 million miles (149.6 million km) 1 ly 5,878 trillion miles (9,460 trillion km) 1 parsec 19,174 trillion miles (30,857 trillion km) astronomical unit (au) kiloparsec (kpc) light day light month light second light year (ly) megaparsec (Mpc) parallax parsec (pc) solar system Key words 9 2 a b 1 c p Journey Apollo to the Moon Furthest flight Apollo to Voyager across (Pioneer 10) Proxima Centauri our galaxy Distance 238,328 miles 7 billion miles 4.2 ly 100,000 ly 383,551.7 km 384,400 km 11 billion km Time 3 days 30 years 900,000 years 1,904,760,000 yrs Traveling distance © Diagram Visual Information Ltd. 2 a b 1 c p Journey Apollo to the Moon Furthest flight Apollo to Voyager across (Pioneer 10) Proxima Centauri our galaxy Distance 238,328 miles 7 billion miles 4.2 ly 100,000 ly 383,551.7 km 384,400 km 11 billion km Time 3 days 30 years 900,000 years 1,904,760,000 yrs Traveling distance
Big bang evidence THE UNIVERSE Big bang theory ● The view that the universe began at a single point in space and time at which all matter and energy came into existence is called the big bang theory. ● It arose in response to the discovery that the universe appears to be constantly expanding. ● A constantly expanding universe suggests that the expansion must have started at some point in the past. ● This point is referred to as the big bang. ● Hubble’s law allows astronomers to extrapolate backwards from the current size and rate of expansion of the universe to determine when the big bang must have occurred. ● The calculation can only be performed by determining a value for Hubble’s constant: the actual rate of expansion. ● Current estimates set the time of the big bang at about 13.7 billion years ago. Big bang concepts ● Matter did not expand out from the big bang into space over a period of time: space and time came into existence with the big bang and have been expanding ever since. ● The universe was very different in the past to what it is now, and will be very different in the future. ● The origins of the big bang itself are unknown. A theory of gravity on very small scales—quantum gravity—is needed to explain processes within the big bang. big bang cosmic microwave background radiation (CMB) element galaxy gravity Hubble’s constant Hubble’s law quantum gravity quasar Key words 10 Cosmic microwave background radiation ● In the early universe temperatures would have been so high that subatomic particles would have been too energetic to form atoms. This would have resulted in a universe opaque to light. ● Evidence for this period appears as cosmic microwave background radiation (CMB): a uniform background haze of radiation at about 2.725 kelvins. Abundance of elements ● The relative abundance of helium-4, helium-3, deuterium, and lithium-7 in the universe are very close to the levels predicted by the theory. ● No other theory attempts to explain why there should be, for example, more helium than deuterium. Quasars and galaxies ● The observable universe is more or less isotropic in space, but not in time. ● Objects at a great distance are seen as they were long ago in the past. Closer objects are seen as they were more recently. ● Different kinds of objects are more often seen at great distances than at close distances, suggesting that they evolved at various stages in the universe’s history when conditions were different. ● For example, no quasars have been observed close to Earth. Beyond a certain distance, many are seen. Beyond a greater distance, there are none. This suggests that quasars only evolved during a certain period. This in turn suggests that the universe is itself evolving. Expansion of space and time since the big bang Beginnings of the universe © Diagram Visual Information Ltd.
THE UNIVERSE Fate of an expanding universe ● If the universe began with the big bang and is currently expanding, there are three possible future scenarios: Closed universe ● The gravitational attraction of all the matter in the universe may be high enough to slow the expansion and eventually reverse it. ● The universe will reach a maximum extent and then contract back to a singularity (the big crunch). Open universe ● If there is insufficient matter in the universe for gravity to slow its expansion, the universe will go on expanding forever. ● Entropy will ensure that, eventually, all star formation will stop, all matter will decay into dispersed subatomic particles, and black holes will evaporate. ● This ultimate conclusion of entropy is known as the heat death of the universe. Static universe ● If there is just enough matter in the universe to slow and eventually stop its expansion, but not enough to cause it to collapse again, the universe will reach a maximum extent and become static. ● In this scenario the universe will also eventually undergo a heat death. Endings of the universe big bang big crunch black hole closed universe dark matter entropy galaxy galaxy cluster galaxy supercluster gravitational attraction heat death MACHO missing mass open universe WIMP Key words 11 Dark matter ● In order to predict the fate of the universe accurately, astronomers must know how much matter it contains. ● The structure of galaxies, galaxy clusters, and galaxy superclusters cannot be explained without assuming that a large proportion of the matter they contain cannot be observed (the missing mass problem). ● This matter is known as dark matter and is thought to make up 90–95 percent of the mass of the universe. ● There are two explanations for what dark matter consists of: ● Massive Compact Halo Objects (MACHOs) are large dense pieces of baryonic matter such as brown dwarfs. ● Weakly Interacting Massive Particles (WIMPs) are elementary particles other than electrons, protons, and neutrons that have mass but interact only very rarely with other matter. ● Current theories suggest that dark matter consists of both MACHOs and WIMPs. Closed universe Open universe Static universe © Diagram Visual Information Ltd.
Bright stars THE UNIVERSE Star magnitude ● Astronomers describe the brightness of a star as its magnitude. ● Apparent magnitude is a measure of how bright a star appears to be in the night sky. This does not distinguish between stars that appear bright because they are close and those that are intrinsically bright. ● Absolute magnitude is a measure of how bright a star would appear to be if it were ten parsecs (32.6 ly) away. This is a measure of a star’s intrinsic brightness. ● For example, Sirius is the brightest star in the sky and Canopus is the second-brightest. In fact Canopus is about 600 times more luminous than Sirius, but it is much farther away so it appears dimmer. ● Absolute magnitude is measured in two ways: if the distance to a star is known, its apparent magnitude can be scaled up or down to match a distance of ten parsecs. Alternatively a star’s luminosity can be estimated according to its spectral type. Magnitude scales ● Stars with lower magnitude measurements (apparent or absolute) are brighter than stars with higher magnitude measurements. ● A magnitude 1 star is brighter than a magnitude 2 star and a magnitude –1 star is brighter still. ● Both magnitude scales are logarithmic: each step in the scale represents a 2.512 multiple increase in brightness. This means that a star of magnitude 1 is 100 times brighter than a star of magnitude 5. absolute magnitude apparent magnitude constellation luminosity magnitude Northern Hemisphere spectral type star Key words 12 Northern Hemisphere sky Signpost to five of the brightest stars Constellation of Orion Betelgeuse Rigel Sirius Procyon Capella Apparent magnitude –1.44 –0.62 –0.01 –0.05 +0.03 +0.08 +0.18 +0.40 +0.45 +0.45 +0.61 +0.76 The 12 brightest stars in the sky Name Sirius Canopus Alpha Centauri Arcturus Vega Capella Rigel Procyon Betelgeuse Achernar Hadar Altair Constellation Canis major Carina Centaurus Boötes Lyra Auriga Orion Canis minor Orion Eridanus Centaurus Aquila Distance (light years) 8.6 313.0 4.39 37.0 25.0 42.0 773.0 11.4 427 144.0 525.0 16.8 Absolute magnitude +1.5 –5.5 +4.1 –0.3 +0.6 –0.5 –6.7 +2.7 –5.1 –2.8 –5.4 +2.2 e d b c f a a b c d e f © Diagram Visual Information Ltd.
THE UNIVERSE Closest stars ● The Milky Way galaxy contains about 200 billion stars. ● About 100 stars lie within 20 light years of the Sun. ● About 30 stars lie within 12 light years of the Sun. ● The closest star, Proxima Centauri, is 4.24 light years from the Sun. Alpha Centauri system ● Proxima Centauri is a member of a triple star system with Alpha Centauri A and Alpha Centauri B, both 4.34 light years from the Sun. ● Proxima Centauri is the dimmest star of the system and is not visible to the naked eye. ● Alpha Centauri A and B are separated by a distance of about 23 au and are not discernible as individual bodies to the naked eye. ● Alpha Centauri A, also known as Rigil Kentaurus, is very similar to the Sun and is the fourth brightest star in the sky. Local space ● The nature and distribution of the stars within 12 light years of Earth allows some conclusions to be made about local space. ● Stars are on average about eight light years apart. ● More than 50 percent of them belong to multiple star systems. ● Most are dimmer than the Sun. Close stars apparent magnitude binary star system constellation galaxy magnitude Milky Way multiple star system Northern Hemisphere star Key words 13 Name 1 Proxima Centauri 2 Alpha Centauri 3 Barnard’s Star 4 Wolf 358 5 Lalande 21185 6 Luyten 726.8 7 Sirius 8 Ross 154 9 Ross 248 10 Epsilon Eridani Of the ten stars closest to Earth only two can be seen with the naked eye from the Northern Hemisphere: Sirius in the constellation Canis Major; Epsilon Eridani in the constellation Eridanus. The ten nearest stars Constellation Centaurus Centaurus Ophiuchus Leo Ursa Major Cetus Canis Major Sagittarius Andromeda Eridanus Apparent magnitude +11.1 –0.01 +9.5 +13.6 +7.7 +12.3 –1.44 +10.5 +12.2 +3.7 Distance (light years) 4.24 4.39 6.0 7.8 8.2 8.5 8.6 9.6 10.3 10.6 Visibility of the nearest stars a b b a © Diagram Visual Information Ltd.
Binary stars ● A binary star system consists of two stars orbiting each other around a common center of mass. ● Three, four, or more stars may orbit each other in the same way. ● Astronomers estimate that about 50 percent of all stars are part of binary or multiple star systems. ● The closest star to the Sun, Proxima Centauri, is part of a triple star system. Binary star types ● Eclipsing binaries are binary systems in which, from the point of view of an observer, one star periodically passes in front of the other . ● Astrometric binaries are binary systems in which only one member of the system is bright enough to be observed. The existence of the other member is inferred by its gravitational effects. ● Contact binaries are binary systems in which both member stars fill their Roche lobes. Their upper atmospheres form a common envelope. ● Detached binaries are binary systems in which both member stars are within their Roche lobes and have no significant effect on each other’s evolution. ● Visual binaries are stars that appear to be members of a binary system from the point of view of an observer, but which are not actually gravitationally linked. ● X-ray binaries are binary systems that periodically emit powerful X-rays. This is thought to occur when one system member is a neutron star or a black hole with an accretion disc formed from material drawn from the other member. Star pairs THE UNIVERSE accretion disc astrometric binary binary star system black hole contact binary detached binary eclipsing binary Lagrange point multiple star system neutron star orbit Roche lobe star visual binary X-ray binary Key words 14 Roche lobe a b c d e Lagrange point The Mizar-Alcor multiple system Alcor (a) takes 10 million years to orbit Mizar (b). Mizar also has two, closer companions (c, d). Alcor also has a close companion (e). Binary system Visual binary Roche lobe © Diagram Visual Information Ltd. ● A Roche lobe is the region around a star in a binary system within which material is gravitationally bound to that star. ● The Roche lobes of two stars in a binary system are tear-shaped volumes of space with their apexes touching at the Lagrange point of the system. ● If a star expands so that some of its surface lies outside of its Roche lobe, that material may be drawn into the Roche lobe of its companion. ● The overflow of material from one Roche lobe into another is thought to be responsible for the formation of accretion discs.
THE UNIVERSE Variable star ● A star that undergoes a great change in luminosity over a relatively short time period is a variable star. ● For comparison, the Sun varies in luminosity by about 0.1 percent over an 11 year cycle but is not considered to be a variable star. ● Some variable stars have regular cycles of variation, others are irregular. Intrinsic variables ● Stars that vary in luminosity because of features intrinsic to those stars are intrinsic variables. ● Mira variables are old, giant red stars. Their luminosity varies because they expand and contract over periods of 100 days or more. ● Cepheid variables are giant yellow stars. Their luminosity varies because they periodically expand and contract. ● Semiregular variables are giant or supergiant stars that have variations in luminosity that are usually regular but can be irregular. ● Irregular variables are stars that vary in luminosity irregularly. Extrinsic variables ● Extrinsic variables are stars that appear to vary in luminosity because of extrinsic factors. ● The most common are eclipsing binary stars in which luminosity is affected by one star passing in front of another. ● Less common are binary systems in which the luminosity of the members is affected by accretion discs and other interactions. Variable stars a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 absolute magnitude accretion disc apparent magnitude Cepheid variable eclipsing binary extrinsic variable galaxy intrinsic variable irregular variable luminosity magnitude Mira variable parallax semiregular variable star variable star Key words 15 Cepheid variables Mira variable Cepheid variable Eclipsing binary ● Cepheid variables are a form of intrinsic variable star. ● They are very useful to astronomers because their period of luminosity variability closely correlates to their absolute luminosity. ● For example, a Cepheid variable with a luminosity period of three days has an absolute luminosity of about 800 Suns. A Cepheid variable with a luminosity period of 30 days has an absolute luminosity of 10,000 Suns. ● These correlations were initially calculated by observing relatively close Cepheid variables whose distances had already been calculated by other methods such as parallax observations. ● Understanding this correlation allows astronomers to determine the distance of a Cepheid variable based solely on its observed period of luminosity. This is done by calculating the distance that a star with a known absolute magnitude (determined by its period of luminosity) must be in order to have its apparent magnitude observed. ● Because Cepheid variables tend to be very bright stars, they are visible across great distances. By determining the distance to a Cepheid variable in another galaxy, astronomers are able to determine the approximate distance to that galaxy as a whole. © Diagram Visual Information Ltd.
Exoplanets THE UNIVERSE Exoplanet ● Exoplanet means “extra-solar planet.” ● An extra-solar planet is a planet in orbit around a star other than the Sun. Finding exoplanets ● More than 130 exoplanets have been confirmed to date. ● None can be observed directly with current technology: they are too dim and distant. ● The first exoplanets were discovered in 1992. Three planets were detected in orbit around the millisecond pulsar PSR B 1257+12 at a distance of about 2,630 light years from Earth. ● Pulsar timing is the detection of irregularities in the pulse periods of pulsars caused by the gravitation effects of planets orbiting them. The first exoplanets were found using this method. ● Astrometery is the measurement of irregularities in the proper motion of stars caused by orbiting planets. Current technologies are not sensitive enough to make this method reliable. ● Doppler method is the measurement of irregularities in a star’s spectral lines caused by orbiting planets. It is best at locating close-orbit planets. ● Gravitational lensing is the detection of the lensing effect of a star and its planets on light from a distant star in the background. It relies on the correct alignment of Earth with the target star and the distant star. ● Transit method is the detection of a planet’s shadow when it passes in front of a star. It also relies on the correct alignment of Earth, star, and planet. astrometry Doppler method exoplanet gas giant gravitational lensing main sequence millisecond pulsar neutron star orbit planet pulsar pulsar timing spectral line star transit method Key words 16 Exoplanet observations ● The oldest exoplanet so far discovered is thought to be about 13 billion years old. That is more than twice the age of Earth and only about one billion years younger than the universe. ● Its existence challenges accepted theories of planet formation. ● Most of the exoplanets discovered so far are gas giants like Jupiter, but have orbits much closer to their stars than Jupiter’s is to the Sun. ● This also undermines assumptions about solar system formation. ● The observed dissimilarity between other solar systems and our own may be due to the limitations of current methods of detection since planets smaller than gas giants cannot yet be reliably detected. © Diagram Visual Information Ltd. Comparison of solar systems Earth’s solar system: gas giants distant from the Sun Newly-discovered solar systems: gas giants much closer to their stars
Stellar evolution THE UNIVERSE Star color ● The variation in the observed color of stars is apparent even to the naked eye. ● Instruments are able to discern very small variations in color between stars. ● The color of a star is closely related to its temperature. Spectral types ● Stars are commonly classified according to their surface temperatures using the Morgan- Keenan spectral classification scheme. ● A mnemonic for the order of the spectral classes (O, B, A, F, G, K, M) is “Oh Be A Fine Girl, Kiss Me.” ● Within each class, stars are further classified with numbers from 0 to 9. For example, A0 denotes the hottest stars in the A class and A9 the coolest. Hertzsprung-Russell diagram ● Different versions of the H-R diagram can show the relationships between absolute magnitude, luminosity, star classification, and surface temperature. ● The majority of stars fall into a few regions of the graph. ● The main sequence is a diagonal spread of stars from the top left to the bottom right of the diagram. ● Stars appear at different points on the diagram at different stages of their life spans. Stellar evolution a b e c d Example Spica (a) Polaris (b) Capella (c) Aldebaran (d) Betelgeuse (e) Color of star Blue White Yellow Orange Red Temperature ºC 30,000–10,000 10,000–7,000 7,000–5,000 5,000–3,000 3,000 Spectral type O, B A, F G K M Luminosity 1,000,000 10,000 100 Sun = 1 0.01 0.0001 Temperature (°C) Sun white dwarfs supergiants giants main sequence Hertzsprung-Russell diagram blue white yellow orange red 20,000 10,000 7,000 6,000 5,000 3,000 absolute magnitude Hertzsprung- Russell diagram luminosity magnitude main sequence Morgan-Keenan classification protostar red giant spectral type star stellar evolution T-Tauri star white dwarf Key words 17 ● As a star evolves over time its position on a Hertzsprung-Russell diagram changes. ● A protostar is cool but very large, so it has a high luminosity. It appears in the top right corner of an H-R diagram. ● Once the star has evolved to become a T-Tauri star, it has contracted and become hotter. It appears very close to the main sequence. ● Once stability has been achieved by hydrogen burning, the star appears within the main sequence. ● Exactly where a star joins the main sequence will depend on its mass. ● More massive stars will be hotter and larger (and therefore more luminous) and will join the main sequence farther to the top left of an H-R diagram than less massive stars. The Sun is at this point in its life and appears near the middle of the main sequence. ● When hydrogen burning stops and helium burning begins, a star rapidly departs from the main sequence as it becomes larger (and therefore more luminous) but cooler. ● A star that reaches a new equilibrium as a red giant or red supergiant appears near the center top of an H-R diagram. ● When helium burning stops in a red giant, the star quickly shrinks in size (and therefore becomes less luminous) until it stabilizes as a white dwarf, which appears near the center bottom of the diagram. © Diagram Visual Information Ltd.
Stellar beginnings THE UNIVERSE Gas cloud ● Most of the empty space in a galaxy actually contains very low concentrations of gas and dust. ● In some regions this concentration is higher: these “clouds” or nebulae are the birthplaces of stars. ● Most clouds are in a state of equilibrium. ● The equilibrium of some clouds may be disrupted by supernova shock waves or the close approach of another cloud or massive object. ● These disruptions may cause changes in the density of parts of the cloud so that gravity overcomes kinetic energy. ● As particles clump together, larger and larger concentrations are formed, which in turn attract more matter. Protostar ● As a cloud contracts, it increases in temperature. Gravitational energy is converted into thermal kinetic energy. ● At first, most of the thermal energy escapes as infrared radiation. ● As the contracting cloud becomes denser, it becomes increasingly opaque to infrared radiation and the rate of heating rises. ● If enough mass is present to raise temperatures to 15,000,000 kelvins, a plasma forms. ● As contraction continues and temperatures rise further, the nuclear fusion of hydrogen may occur. Brown dwarf ● If not enough mass is present to generate the temperatures needed for nuclear fusion, a brown dwarf results. ● Brown dwarfs typically have masses between 13 and 75 times the mass of Jupiter. ● Some astronomers believe that brown dwarfs may be the most common objects in our galaxy. brown dwarf galaxy gravitational attraction infrared nebula nuclear fusion plasma protostar star supernova Key words 18 Gas cloud Protostar Contracting gas cloud © Diagram Visual Information Ltd.
THE UNIVERSE T-Tauri star ● If temperatures become high enough for the nuclear fusion of hydrogen nuclei to occur, a protostar becomes a T-Tauri star. ● T-Tauri stars are situated just above the main sequence on a Hertzsprung- Russell diagram. ● Their fusion processes are restricted to a small central core. ● The star is still contracting gravitationally and some material is still falling onto its surface from an accretion disc. ● Strong winds push some material away and the star may emit polar jets of energetic radiation. ● Equilibrium has not been achieved. Mature star ● Eventually, the outward pressure generated by nuclear fusion balances the inward pressure of gravitation and the star achieves a stable diameter. ● Equilibrium is achieved and the star is situated on the main sequence of an H-R diagram. Life span ● The stable phase of a star’s life is usually its longest. ● This is because the nuclear fusion of hydrogen into helium is the most efficient of the nuclear burning stages. ● The length of time that a star remains in the main sequence is closely related to its mass. ● More massive stars have shorter spans of stable maturity than less massive stars. Stellar birth accretion disc core Hertzsprung- Russell diagram main sequence mature star nuclear fusion polar jet protostar star T-Tauri star Key words 19 T-Tauri star Polar jets Mature star and disc of leftover material © Diagram Visual Information Ltd.
Regular star death THE UNIVERSE Red giant ● Once all the hydrogen in a star has undergone nuclear fusion into helium, fusion processes stop. ● Without the outward pressure generated by fusion, the star undergoes rapid gravitational contraction. ● This contraction raises the temperature and density of the core until the nuclear fusion of helium nuclei becomes possible. ● The pressure generated by helium fusion forces the star to expand again. ● A new equilibrium is reached, leaving the star with a diameter 100–200 times greater than it was during the hydrogen burning phase. ● The surface temperature and overall density are lower, but the density of the core is higher. White dwarf ● Once all the helium in a red giant has been fused into carbon, fusion processes stop again. ● The star undergoes rapid gravitational contraction again. ● If the star has a mass of less than about 3.4 times the mass of the Sun, this contraction will not produce enough heat to initiate the fusion of carbon nuclei. ● The star’s outer layers (about 80 percent of its mass) are ejected to form a planetary nebula. ● The remaining mass (about 20 percent of its original mass) contracts to form a white dwarf. ● It is thought that white dwarfs eventually cease shining, and become black dwarfs. black dwarf core nuclear fusion planetary nebula red giant white dwarf Key words 20 Mature star Red giant Planetary nebula White dwarf Black dwarf © Diagram Visual Information Ltd.
THE UNIVERSE Large star death 21 Red supergiant ● Massive stars evolve into stars burning helium in the same way as stars with masses similar to the mass of the Sun. ● They swell to sizes much greater than those achieved by Sun-like stars and are known as red supergiants. ● Their greater masses allow them to achieve temperatures at which carbon and other, heavier, elements undergo nuclear fusion. ● Helium is fused into carbon, carbon into oxygen, oxygen into silicon, and silicon into iron. ● Massive stars are likely to suffer a supernova explosion once sustained fusion can no longer take place. Chandrasekhar limit ● The Chandrasekhar limit describes the maximum sustainable mass of a white dwarf: about 1.44 times solar mass. ● This is the mass at which a body’s tendency to contract due to gravitation can no longer be balanced by degeneracy pressure. ● This limit defines whether the core of a star will collapse to become a white dwarf, a neutron star, or a black hole. ● It refers only to that portion of a star’s mass that undergoes gravitational collapse when fusion reactions stop. ● For example, a massive star may lose a large proportion of its mass in the form of a planetary nebula and the remaining mass may be below the Chandrasekhar limit. Type I and II supernovas ● Type II supernovas result from the gravitational collapse of massive stars. ● Type I supernovas result when a white dwarf in a binary star system acquires additional mass from another star in that system, which causes it to exceed its Chandrasekhar limit. ● Type I supernovas are many times more powerful than Type II supernovas. binary star system black hole core neutron star nuclear fusion red supergiant supernova white dwarf Key words Mature star Red supergiant Type II supernova Neutron star © Diagram Visual Information Ltd.
Giant star death THE UNIVERSE Giant stars ● The most massive stars undergo the same stages of evolution as large stars. ● No star is thought to be large enough to enable the sustained nuclear fusion of iron to occur in its core. ● Giant stars are eventually torn apart in supernova explosions. Supernova ● At the point where no more fusion reactions are possible the core of a red supergiant undergoes a very rapid gravitational collapse. ● The core collapses to a diameter of about six miles (10 km) in a fraction of a second. ● Material from the outer envelope collapses more slowly and is thought to rebound from the collapsed core. ● This rebound is incredibly energetic and causes the envelope to be ripped apart and ejected in a supernova. ● A supernova may release more energy in a second than the Sun will produce in its entire 10 billion-year life span. ● The surviving core may be a neutron star or, if it is more massive, may collapse further to become a black hole. Supernova seeding ● Only massive stars form relatively heavy elements such as oxygen, silicon, and iron through the fusion of lighter, more abundant elements. ● When a supernova occurs, these heavy elements are ejected into interstellar space at high speeds. ● Planets such as Earth, and the living things that exist on it, are partly made up of these heavy elements. ● Without red supergiant fusion and the subsequent seeding of its fusion products, rocky planets and life may not be possible. black hole core neutron star nuclear fusion red supergiant star supernova Key words 22 Mature star Red supergiant Type II supernova Black hole © Diagram Visual Information Ltd.
THE UNIVERSE Neutron star ● A neutron star is a small but extremely dense object composed almost entirely of neutrons. ● A neutron star may be only six miles (10 km) in diameter but have between 1.4 and three times the mass of the Sun. ● Neutron stars are thought to be the collapsed remnants of massive stars that have exploded in supernovas. Neutron star features ● Neutron stars rotate very rapidly. The most rapid have rotation periods of hundredths of a second and the slowest of 30 seconds. ● This rapid rotation is due to the conservation of angular momentum: the slow rotation of the original massive star speeds up as the object shrinks. ● Rotation periods very slowly become longer over time: younger neutron stars rotate more rapidly than older ones. Neutron star types ● Magnestars are neutron stars with magnetic fields that are at least 1,000 times more intense than Earth’s. Their magnetic fields become weaker over time. ● X-ray bursters are neutron stars that have accretion discs formed from material drawn from orbiting companion stars. Friction in the accretion disc results in the periodic emission of powerful X-ray bursts. Neutron stars accretion disc exoplanet gamma ray magnestar millisecond pulsar neutron star orbit pole pulsar supernova X-ray X-ray burster Key words 23 Pulsars ● Pulsars are neutron stars that emit a stream of X-rays and gamma rays from their poles. These are recorded as regular pulses whenever an observer is in line of sight of one of the poles. ● As with all neutron stars, a pulsar’s rate of rotation slows as time passes. As its rotation slows, the frequency of the pulses is also reduced. ● However, millisecond pulsars are very old pulsars (one billion years or more) with very high rotation rates (pulse periods of less than 25 milliseconds). ● Millisecond pulsars are thought to form when material from a companion star falls onto a pulsar, causing it to spin more and more rapidly. ● The first exoplanets to be discovered are in orbit around millisecond pulsars. Manhattan Island neutron star Size By comparing a neutron star with Manhattan Island on the same scale, the neutron star’s very small size can be visualized. A cubic centimeter of matter from a neutron star would weigh about as much as 3,500 fully-laden Saturn V rockets on Earth. Mass A neutron star is the result of the collapse of a giant star many millions of times larger in size. As a result of this compression, neutron stars are very dense. 12 Miles 6 0 © Diagram Visual Information Ltd.
Cygnus X-1 An X-ray source known as Cygnus X-1 may be related to the presence of a black hole in orbit around the star Eta Cygni. a blue giant star Eta Cygni b proposed orbiting black hole c material drawn from Eta Cygni by the black hole’s gravitation d heated material gives off X-rays as it accelerates toward the black hole c b d a Black holes THE UNIVERSE Black holes ● A black hole is a region of space with a gravity field so strong that nothing, including light, can escape from it: it has an escape velocity greater than the speed of light. ● A black hole is thought to result from the gravitational collapse of a massive star at the end of its life. ● Black holes may also be created in the centers of young galaxies. Black hole features ● No matter or information can flow from the inside of a black hole to the outside universe. ● The event horizon is the “surface” of a black hole. It is the perimeter at which the escape velocity is exactly the speed of light. ● At the center of a black hole there is a singularity where gravity and escape velocity become infinite. ● Astronomers suspect there are two classes of black hole: stellar mass and supermassive. ● Stellar mass black holes have masses between four and 15 times the mass of the Sun. ● Supermassive black holes have masses many billions of times greater than the Sun. ● Supermassive black holes are thought to form at the centers of active galaxies. accretion disc active galaxy axis black hole blue shift escape velocity event horizon galaxy gravitational lensing pole red shift singularity star stellar mass black hole supermassive black hole X-ray Key words 24 Detecting black holes The evidence ● Only indirect evidence for black holes has been observed. ● Evidence for the existence of black holes comes from the observation of phenomena close to where a black hole might be. Accretion disc ● Matter falling toward a black hole, but still outside the event horizon, is thought to form a rapidly spinning accretion disc. ● Friction between different zones of the accretion disc is thought to cause the emission of large amounts of X-rays. ● Narrow jets of particles moving at close to the speed of light are thought to be emitted along the polar axis of an accretion disc. Red and blue shifts ● Material orbiting a black hole would be moving away from an observer for one half of its orbit and toward the same observer for the other half. ● Velocity and direction of motion can be ascertained by measuring the blue shift or red shift of its emissions. ● Material orbiting a supermassive black hole at very high speeds would exhibit a large red shift on one half of its orbit and a large blue shift on the other. Other evidence ● Stars that appear to be orbiting a region of space where no matter is visible may be orbiting black holes. ● Gravitational lensing may distort light from objects behind and far beyond a black hole. © Diagram Visual Information Ltd.
THE UNIVERSE Quasars ● The word quasar is derived from “quasi-stellar radio source.” ● Quasars are also known as QSOs or quasi-stellar objects. ● They appear as bright blue point sources through an optical telescope. ● Some have strong radio emissions (they are “radio loud”) but most do not (they are “radio quiet”). Quasar features ● The emissions from all quasars exhibit very high red shifts, indicating that they are very distant and therefore receding at very high velocities. ● Despite their great distance, they are very bright. ● A typical quasar has the same luminosity as about 1,000 Milky Way galaxies. ● Quasar luminosities vary over time periods of months, weeks, days, or hours. ● These relatively short periods of variation in luminosity indicate that they are relatively small (no effect can propagate across an object faster than the speed of light). ● Taken together, these features indicate that quasars are about the size of the solar system, but emit as much energy as a thousand large galaxies. Quasar origins ● Quasars are thought to be the active cores of very ancient galaxies. ● Their energy is thought to be produced by the effects of supermassive black holes on matter surrounding them. Quasars c b a d e red shift blue shift a A distant star receding from Earth at high velocity. b Light waves emitted in front of the star are squashed closer together. c An observer aboard a craft in the path of the star sees a blue-shifted image of the star. d Light waves emitted behind the star are stretched further apart. e An observer on Earth sees a red-shifted image of the star. blue shift galaxy luminosity Milky Way quasar quasi-stellar object (QSO) radio loud radio quiet red shift solar system star supermassive black hole Key words 25 Red shift and blue shift ● Red shift is a phenomenon used by astronomers to determine the distance of objects. ● Light travels in waves and its color depends upon its wavelength. When an object, such as a star, moving at high velocity gives out light, the light waves ahead of it are squashed closer together and the light waves behind it are stretched further apart. ● Light with longer (stretched) wavelengths is redder. Light with shorter (squashed) wavelengths is bluer. ● Objects receding from an observer at high velocity appear to be redder than they actually are (called red shift). ● The faster an object is receding from Earth the larger its red shift. The faster an object is traveling the farther away it must be, if it is true that the universe is constantly expanding. c b a d e red shift blue shift a A distant star receding from Earth at high velocity. b Light waves emitted in front of the star are squashed closer together. c An observer aboard a craft in the path of the star sees a blue-shifted image of the star. d Light waves emitted behind the star are stretched further apart. e An observer on Earth sees a red-shifted image of the star. c b a d e red shift blue shift a A distant star receding from Earth at high velocity. b Light waves emitted in front of the star are squashed closer together. c An observer aboard a craft in the path of the star sees a blue-shifted image of the star. d Light waves emitted behind the star are stretched further apart. e An observer on Earth sees a red-shifted image of the star. c b a d e red shift blue shift c b a d e red shift blue shift © Diagram Visual Information Ltd.
The Milky Way THE UNIVERSE black hole galactic center galactic plane galaxy globular cluster Local Arm Milky Way spiral galaxy supermassive black hole Key words 26 The Milky Way ● The Milky Way is visible as an irregular band of faint light across the night sky. ● This band is the arm of our galaxy in which the Sun is located. ● Astronomers refer to our galaxy as a whole as the Milky Way. Our galaxy ● Our galaxy is a spiral galaxy with four major arms. ● It is thought to be unusually large. ● It contains about 100 billion stars. ● The central bulge is densely populated with old red stars. ● The arms are mostly populated by young blue stars. ● A spherical halo of old dull stars surrounds the main disc. ● Clusters of old stars (between 10,000 and a million) known as globular clusters also surround the main disc. ● Some astronomers believe there may be a supermassive black hole at the galactic center. The Sun’s place ● The Sun is situated in one of the Milky Way’s spiral arms known as the Orion or Local Arm. ● It is about 28,000 light years from the galactic center and about 20 light years above the center of the galactic plane. Components of the Milky Way 1 A dense bulging center with a high concentration of stars. 2 A surrounding halo of stars. 3 Trailing arms with less concentration of stars. 4 Our Sun, about 30,000 ly from the center. 4 3 100,000 light years 2 1 2,000 light years © Diagram Visual Information Ltd.
THE UNIVERSE Galaxy ● A galaxy is a collection of stars, gas, and dust bound together by gravity. ● The universe contains many billions of galaxies. ● They typically contain millions to hundreds of billions of stars. ● There are four main types: elliptical, spiral, barred spiral, and irregular. Elliptical galaxies ● Elliptical galaxies are the most common kind of galaxy. ● They have a smooth rounded appearance, without complex regular structural features. ● They contain little gas or dust. ● They contain few hot bright stars and many dull old stars. Spiral galaxies ● Spiral galaxies resemble a flattened disc with outlying spiral arms in the same plane. ● The central disc is dense and contains mainly older stars. ● The spiral arms contain gas, dust, and younger stars. ● They are surrounded by a halo of older stars and dense clusters of older stars. ● Our galaxy is a spiral galaxy. Barred spiral galaxies ● A barred spiral galaxy is a spiral galaxy in which the arms originate from the ends of a bar through the galactic core. Irregular galaxies ● Irregular galaxies have no regular shape or symmetrical features. ● Many contain a lot of gas, dust, and young stars. Galaxy types barred spiral galaxy elliptical galaxy galaxy gravity irregular galaxy spiral galaxy star Key words 27 NGC 1300 in Eridanus M 51: the Whirlpool galaxy Large Magellanic Cloud NGC 4472 in Virgo Elliptical galaxy Spiral galaxy Irregular galaxy Barred spiral galaxy © Diagram Visual Information Ltd.
Galaxy groups THE UNIVERSE Clusters ● Galaxies are not randomly distributed in space. ● They are clumped together in groups, clusters, and superclusters. ● A group contains fewer than 50 galaxies and has a diameter of about two Megaparsecs (Mpc). ● A cluster contains 50–1,000 galaxies and has a diameter of about eight Mpc. ● A supercluster contains thousands of clusters and groups and may be millions of megaparsecs in extent. Voids, sheets, and filaments ● About 90 percent of space seems to consist of bubble-like voids in which very few galaxies are observed. ● Most voids are about 25 Mpc in diameter. The largest known, the Boötes void, has a diameter of about 124 Mpc. ● Galaxies are concentrated in sheets and filaments separated by these voids. ● Superclusters occur at the intersections of sheets and filaments. ● No structures larger than superclusters have been confirmed. Local group ● The Milky Way is a member of the Local Group of galaxies, which consists of about thirty other galaxies including the Andromeda galaxy and the Large and Small Magellanic Clouds. ● The Local Group is a member of the Virgo or Local Supercluster, which consists of about 100 other groups and clusters of galaxies, including the Virgo cluster. 28 Distribution of galaxies 1 million light years 1 billion light years © Diagram Visual Information Ltd. galaxy galaxy cluster galaxy group galaxy supercluster local group Local Supercluster Milky Way Key words
THE UNIVERSE Hubble’s law ● U.S. astronomer Edwin Hubble (1889–1953) proved the existence of galaxies other than our own. ● He discovered that the universe is many times larger than previously thought. ● Red shift analysis showed that all objects outside our galaxy were receding. ● More distant objects were receding at greater velocities. ● He concluded that the universe is constantly expanding in all directions. ● Hubble’s law states: the further away an object is, the faster its rate of recession, and that this relationship is constant. Hubble’s constant ● Hubble’s constant is the actual ratio of the speed of recession of an object to its distance from the observer. Hubble’s law 29 Hubble’s constant The raisin cake analogy ● In an uncooked raisin cake (1) one raisin is chosen to represent Earth and the distances from it to other raisins in the cake are measured. ● After an hour, yeast in the cake has caused it to expand uniformly in all directions so that it is now twice the size (2). ● The distances between the “Earth” raisin and the other raisins are measured again and all distances are now twice what they were before. This means that more distant raisins have covered much larger distances relative to the “Earth” raisin than nearby raisins . They have covered this distance in the same time, so they are moving at a greater velocity than nearby raisins. 100,000 80,000 60,000 40,000 20,000 0 0 300 1,200 Distance Velocity 1,500 600 900 kma s–1 megaparsecs 1 2 a b c b b b c a a © Diagram Visual Information Ltd. galaxy Hubble’s constant Hubble’s law red shift Key words
THE SUN’S FAMILY ecliptic gas giant inner planet orbit planet rocky planet solar system solar wind Key words 30 Beginnings of the solar system Observations ● A good theory of solar-system formation has to explain certain facts observed in our own solar system: ● In our own solar system the planets orbit very close to the plane of the ecliptic (the plane of Earth’s orbit around the Sun). ● All of the planets orbit around the Sun in the same direction. ● The inner planets are much smaller and have very different compositions to the outer gas giants. Modern theory ● The Sun was formed from a condensing cloud of gas and dust. ● As this cloud shrank, any rotation it had would have been accelerated by the conservation of angular momentum. ● This caused the cloud to flatten into a broad rotating disc. The planets are thought to have formed from material in the outer part of this disc. The Sun is thought to have formed from material in the inner part of the same disc. ● Temperatures were higher in the regions of the disc closer to the proto- Sun than they were in more distant regions. ● Higher temperatures and a strong solar wind would have driven lighter elements out of the inner solar system allowing only small dense planets to form. ● Lower temperatures farther away from the proto-Sun would allow lighter elements to clump together, resulting in large gaseous planets. a c Sun rocky planets frost line gaseous planets a b c d 0.3 au 3.5 au d b Temperature and formation of the solar system Two types of planet ● Within about 0.3 au of the Sun temperatures are too high for rocks, metals, or hydrogen compounds to exist as solids. No planets have been formed within this limit. ● Between about 0.3 au and 3.5 au of the Sun temperatures are low enough for rocks and metals to condense as solids, but too high for hydrogen compounds to do so. Rocky planets have formed within this band. ● Beyond about 3.5 au of the Sun (known as the “frost line”) temperatures are low enough for hydrogen compounds such as CO2 and H2O to condense as solids. Gaseous planets have formed beyond this limit. © Diagram Visual Information Ltd.
THE SUN’S FAMILY Terrestrial planets ● The terrestrial planets, or rocky planets, are those similar in size and composition to Earth. ● They are smaller and denser than the Jovian planets. ● The terrestrial planets are Mercury, Venus, Earth, and Mars. ● They orbit closest to the Sun. Jovian planets ● The Jovian planets, or gas giants, are those similar in size and composition to Jupiter: Saturn, Uranus, and Neptune. ● They are larger and less dense than the terrestrial planets. ● They orbit farthest from the Sun. Trans-Neptunian objects ● A trans-Neptunian object is any object within the solar system with an orbit that is entirely or mostly beyond the orbit of Neptune. ● Pluto is classified as a trans-Neptunian object. Some astronomers believe that Pluto is too dissimilar to the other planets to be classified as a planet in its own right. ● Pluto is believed to consist mostly of ice and has a highly irregular orbit. ● Several other recently discovered bodies, including Sedna, Quaoar, and Varuna are similar in composition, size, and orbit to Pluto but are not regarded as planets. ● It is likely that, if Pluto were discovered today, it would not be classified as a planet. Sizes gas giant Jovian planet orbit rocky planet terrestrial planet trans-Neptunian object (TNO) Key words 31 Planet Diameter miles (km) Pluto 1,420 (2,280) Mercury 3,030 (4,879) Mars 4,220 (6,790) Venus 7,520 (12,100) Earth 7,930 (12,760) Planet Diameter miles (km) Neptune 30,780 (49,530) Uranus 31,760 (51,120) Saturn 74,900 (120,540) Jupiter 89,350 (142,980) a b c d e f g h i i a b c d e f g h © Diagram Visual Information Ltd.
Distances THE SUN’S FAMILY Sun distances ● Each planet’s distance from the Sun varies because each has an elliptical orbit. ● Planetary distances are commonly given as their mean distances from the Sun during the course of an orbit. ● Pluto has the most eccentric orbit: for about 20 years of its 248-year orbits it is closer to the Sun than Neptune. Earth distances ● The distances between Earth and the other planets constantly change because the orbits of the planets are not synchronized. ● For example, when Venus is on the same side of the Sun as Earth it approaches Earth to within 26 million miles (42 million km), but when it is on the opposite side of the Sun it reaches a distance of about 160 million miles (258 million km). Distance visualization ● The inner planets are much more closely grouped together than the outer planets. ● The mean distance between Mars, the last of the inner planets, and Jupiter, the first of the outer planets, is three times greater than the space that spans the mean orbits of the inner planets combined. ● On average the mean distances between the orbits of the outer planets is about 22 times greater than the mean distances between the orbits of the inner planets. eccentricity inner planet outer planet orbit planet Key words 32 Mean distance from the Sun millions of miles (km) Neptune 2,790 (4,450) Uranus 1,780 (2,870) Saturn 886 (1,430) Mars 140 (230) Venus 67.2 (108) Mercury 36 (57.9) Earth 93 (150) Jupiter 483 (778) Mean distance from Earth millions of miles (km) Neptune 2,677 (4,308) Uranus 1,606 (2,585) Saturn 744 (1,197) Mercury 50 (80.5) Mars 35 (56.3) Venus 25 (40.2) Jupiter 367 (591) Pluto 2,670 (4,297) Pluto 3,700 (5,900) © Diagram Visual Information Ltd.
THE SUN’S FAMILY Temperature ● The average temperature on the surface of a planet is determined by two main factors: ● The first factor is the distance from the Sun. The closer a planet’s orbit lies to the Sun, the more heat it receives. ● Atmospheric composition is the second factor. This determines how much of the Sun’s heat is retained. ● Earth and the Moon receive about the same amount of heat from the Sun. Since the Moon has no appreciable atmosphere however, very little of that heat is retained. ● Mercury is closer to the Sun than Venus, but average surface temperatures on Venus are higher than they are on Mercury because the composition of Venus’ atmosphere traps heat. Albedo ● Albedo is a measure of the reflectiveness of a planet or other celestial body. ● It is expressed as a percentage of the amount of sunlight that a body reflects back into space. ● Earth has an average albedo of about 38 percent. The Moon has an albedo of about 12 percent. ● Different regions have different albedos. A snow-covered landscape may have an albedo of 90 percent, but a deciduous forest only has about 13 percent. ● Albedo has a significant influence on surface temperatures. Temperatures albedo atmosphere orbit planet Key words 33 Masses of the planets Planet Mass Pluto 0.002 Mercury 0.06 Mars 0.11 Venus 0.82 Earth 1.0 Uranus 14.6 Neptune 17.2 Saturn 95.2 Jupiter 317.9 a b c d e f g h i Venus 864°F (462°C) Mercury –279° to +801°F (–173° to +427°C) Earth 57°F (14°C) Mars –225° to 63°F (–143° to 17°C) Jupiter –250°F (–157°C) Saturn –288°F (–178°C) Uranus –357°F (–216°C) Neptune –353°F (–214°C) Pluto –387° to –369°F (–233° to –223°C) Planet Average surface temperature °F (°C) a b c d e f g h i Surface temperatures of the planets Approximate Earth mass = 6,000,000,000,000,000,000,000 tons a b c d e f g h i b °C °F 900 800 700 600 500 400 300 200 100 0 –100 –200 –300 –400 450 400 350 300 250 200 150 100 0 50 –50 –100 –150 –200 c d e f g h i a © Diagram Visual Information Ltd.
Orbits THE SUN’S FAMILY Describing orbits ● Rotational period is the time taken for a planet to complete one revolution on its axis (a local day). ● Sidereal period is the time taken for a planet to make one orbit of the Sun (a local year). ● Orbital speed is the average velocity at which a planet orbits the Sun. ● Eccentricity is a measure of how far an orbit departs from being a perfect circle (all planetary orbits are ellipses). ● Inclination is the angle between the plane of a planet’s orbit and a fixed reference plane (usually the plane of Earth’s orbit around the Sun, known as the ecliptic). Observations ● All the planets except Pluto orbit in planes very close to the ecliptic. ● All the planets orbit in the same direction around the Sun. ● Pluto has the largest eccentricity to its orbit. ● All the planets except Venus have rotational periods shorter than their sidereal periods (a local day is longer than a local year on Venus). axis eccentricity ecliptic inclination orbit orbital speed planet rotational period sidereal period Key words 34 Days (Earth) a b c d e f g h i Mercury 28.74 (46.24) Venus 21.0 (33.78) Earth 17.88 (28.77) Mars 14.46 (23.27) Jupiter 7.86 (12.65) Saturn 5.76 (9.27) Uranus 4.08 (6.56) Neptune 3.24 (5.21) Pluto 2.82 (4.54) Rotation periods Orbital speeds Sidereal periods Planet Miles per sec (km per sec) Planet Earath years Earth days Mercury 88.0 Venus 224.7 Earth 365.256 Mars 687.0 Jupiter 11.86 Saturn 29.46 Uranus 84.01 Neptune 164.80 Pluto 248.54 a b c d e f g h i Planet Mercury 59 Venus 243 Earth Mars Jupiter Saturn Uranus Neptune Pluto 6 Minutes Hours 0 0 23 24 9 10 17 16 0 0 0 56 37 55 39 8 7 0 Planetary orbits The yellow line indicates the distance traveled around the Sun in one Earth year. © Diagram Visual Information Ltd.
THE SUN’S FAMILY Moon ● A moon is a natural satellite of a planet, although the natural companions of some non-planets (such as asteroids) may also be referred to as moons. ● There are more than 140 recognized moons in the solar system and more are continually being discovered. ● Mercury and Venus do not have moons. ● Earth has one large satellite (the Moon). Some astronomers refer to Earth and the Moon as a binary planet system because of the relatively large size of the Moon. ● Mars has two small irregularly shaped moons. ● The Jovian planets each have large numbers of moons. ● Pluto has one large and two much smaller moons. It is also considered to be part of a binary planet system by some astronomers because of the relative size of its largest moon, Charon. ● Theories of planet formation suggest that planets outside of the solar system, known as exoplanets, should also have moons, but none have yet been detected. Moon orbits ● All moons are tidally locked to the planets they orbit. ● No moons have moons of their own because the orbit that the moon of a moon would have to occupy would be inherently unstable. Moons asteroid binary planet system exoplanet Jovian planet moon orbit planet satellite solar system tidally locked Key words 35 Number of known moons Kahoolawe, Hawaii Deimos, Mars Moons can be larger than planets: Mercury is 3,030 miles (4,879 km) in diameter Pluto is 1,420 miles (2,280 km) in diameter Moon Of planet Diameter miles (km) Ganymede Jupiter 3,293 (5,270) Titan Saturn 3,200 (5,120) Callisto Jupiter 3,012 (4,820) Io Jupiter 2,286 (3,659) Europa Jupiter 1,906 (3,050) d e f g a b c Sizes of moons g f e d c a b g f e d c Island of Grenada Phobos, Mars a b a b c d e f g Planet Number of moons Earth 1 Mars 2 Jupiter 63 Saturn 49 Uranus 27 Neptune 13 Pluto 3 © Diagram Visual Information Ltd.
Gravities THE SUN’S FAMILY Gravity ● Gravity is the tendency of masses to move toward each other. ● Gravitational attraction is the way in which this tendency is usually described. According to Albert Einstein’s generally accepted theory of gravity there is no such force as gravitational attraction, but the phrase is used when discussing the motion of celestial bodies and spacecraft. ● The gravitational attraction exerted by a body depends on its mass. More massive bodies exert greater gravitational attraction than less massive bodies. Planet gravities ● Because the planets have different masses, their gravitational attractions are also different. ● For example, it takes less energy to launch a spacecraft from the surface of Mars into orbit than it does to launch the same spacecraft from the surface of Earth. This is because Earth has a greater mass and therefore a greater gravitational attraction than Mars. gravitational attraction gravity orbit planet Key words 36 Planet Height Planetary high jumps An athelete capable of making a vertical jump of 3 feet (0.91 m) on Earth would achieve these heights on the other planets. Jupiter 1 foot 3.5 inches (0.39 m) Neptune 2 feet 6.5 inches (0.77 m) Uranus 2 feet 6.75 inches (0.78 m) Saturn 2 feet 7.25 inches (0.79 m) Venus 3 feet 4.75 inches (1.04 m) Mars 7 feet 10.75 inches (2.41 m) Mercury 8 feet 1.25 inches (2.47 m) Pluto Not known e f g h ? b c d e f g Planet Comparative gravity (Earth gravity = 1.0) Jupiter 2.64 Neptune 1.2 Uranus 1.17 Saturn 1.15 Planet Comparative gravity (Earth gravity = 1.0) Venus 0.88 Mars 0.38 Mercury 0.38 Pluto Not known a b c d e f g h e f g h d c b a Earth a b c d a © Diagram Visual Information Ltd.
aphelion atmosphere axis equator greenhouse gas orbit perihelion pole rotational period sidereal period THE SUN’S FAMILY Key words 37 Planet summaries Pluto Neptune Uranus Mars Jupiter Saturn 74,900 miles (120,540 km) 886 million miles (1,430 million km) –288°F (–178°C) 10 hours 39 minutes 29.46 years Diameter Mean distance from Sun Surface temperature Rotation period Sidereal period 4,220 miles (6,790 km) 140 million miles (230 million km) –225° to +63°F (–143° to +17°C) 24 hours 37 minutes 687 days 89,350 miles (142,980 km) 483 million miles (778 million km) –250°F (–157°C) 9 hours 55 minutes 11.86 years 7,930 miles (12,760 km) 93 million miles (150 million km) 57°F (14°C) 23 hours 56 mins 365.26 days 3,030 miles (4,879 km) 36 million miles (57.9 million km) –279° to +801°F (–173° to +427°C) 59 days 88 days Diameter Mean distance from Sun Surface temperature Rotation period Sidereal period 7,520 miles (12,100 km) 67.2 million miles (108 million km) 864°F (462°C) 243 days 224.7 days 30,780 miles (49,530 km) 2,790 million miles (4,450 million km) –353°F (–214°C) 16 hours 7 minutes 164.80 years 1,420 miles (2,280 km) 3,700 million miles (5,900 million km) –387° to –369°F (–233° to 223°C) 6 days 248.54 years Diameter Mean distance from Sun Surface temperature Rotation period Sidereal period 31,760 miles (51,120 km) 1,780 million miles (2,870 million km) –357°F (–216°C) 17 hours 8 minutes 84.01 years Mercury Venus Earth © Diagram Visual Information Ltd. Diameter ● None of the planets in the solar system are perfect spheres. ● The equatorial diameters of all of the planets are slightly greater than their polar diameters. Mean distance from the Sun ● The orbits of all of the planets are elliptical. ● This means that there is a point on a planet’s orbit where it makes its closest approach to the Sun and a point where it is at its most distant. ● The closest point to the Sun is known as aphelion and the most distant point as perihelion. Surface temperature ● Planets closer to the Sun are generally warmer than planets farther away from the Sun, but the nature of a planet’s atmosphere has a great impact on surface temperature. ● For example, Venus has a very thick atmosphere laden with greenhouse gases, which gives it a very high and almost constant surface temperature. Mercury is much closer to the Sun but has a very thin atmosphere that does not trap heat. Consequently there is a great temperature difference between the side of Mercury facing the Sun and the side facing away from it. Rotational period ● A planet’s rotational period is the length of time it takes that planet to rotate once on its axis. This can be thought of as a local “day.” Sidereal period ● A planet’s sidereal period is the length of time it takes to complete one orbit around the Sun. This can be thought of as a local “year.” Not all planets have sidereal periods (years) that are longer than their rotational periods (days).
Sunspots and flares THE SUN’S FAMILY Sunspots ● A sunspot is a region of the Sun’s surface that is cooler than its surroundings at about 8,500°F (4,700°C) rather than 10,300°F (5,700°C). ● They are darker because they are cooler. ● Sunspots are also slight depressions in the Sun’s surface. ● They are associated with magnetic fields surrounding the Sun. ● Different parts of the Sun’s surface rotate at different speeds, which results in lines of magnetic flux becoming twisted, with their ends puncturing the Sun’s surface. These puncture points are sunspots. ● Sunspots appear in pairs, each with opposite magnetic polarity, and fade after about two weeks. Solar flares ● A solar flare is a rapid and energetic eruption of material from the Sun’s surface. ● They are explosive events that typically last for no more than a few minutes. ● Solar flare strength is categorized as A, B, C, D, M, or X (with X being the most powerful). Each class is ten times more powerful than the preceding class. ● Increased solar flare activity corresponds with increased sunspot activity. ● The streams of energized particles emitted in a solar flare may interact with Earth’s atmosphere and cause interference with electronic and radio equipment. atmosphere solar flare sunspot Key words 38 Sunspot migration New sunspots aligned on the Sun’s surface. After time the Sun has revolved on its axis. Sunspots near the Sun’s equator have traveled a greater distance than those near the poles. Elements of a solar flare 1 2 1 2 Typical sunspot distribution a b c electromagnetic radiation a b electrons protons c © Diagram Visual Information Ltd.
THE SUN’S FAMILY Solar wind ● Solar wind is the high-energy plasma constantly emitted into space from the surface of the Sun. ● It consists of a stream of ionized particles (mostly protons) with the same composition as the Sun’s corona. The volume of space influenced by the solar wind is known as the heliosphere. ● The heliopause is the boundary of the solar wind’s influence. ● The actual distance of the heliopause from the Sun is unknown. It certainly lies far beyond the orbit of Pluto. ● The position of the heliopause probably varies depending on the density of the local interstellar medium and the velocity of the wind. Solar prominences ● A solar prominence is a prominent structure of energetic material formed in the Sun’s chromosphere. ● An eruptive prominence is an arched structure following lines of magnetism that may persist for several hours. ● A quiescent prominence is a patch of energized gas that hangs in the Sun’s chromosphere for days. ● Prominences are associated with sunspots. Solar wind atmosphere chromosphere corona eruptive prominence galactic center heliopause heliosphere interstellar medium magnetosphere magnetotail orbit planet quiescent prominence solar prominence solar system solar wind sunspot Key words 39 Sun solar winds moving along lines of magnetism “bow shock” region where solar wind is deflected by the magnetosphere magnetosphere (Earth’s magnetic field) Earth distortion of the magnetosphere by solar wind creates a magnetotail interstellar gases and radiation deflected by heliosphere Solar wind eruptive prominence surface of the Sun sunspot group a b c Solar prominence a b c a b c e f g d a b c d e f g © Diagram Visual Information Ltd.
THE SUN’S FAMILY Atmosphere ● Mercury has a trace atmosphere consisting of oxygen, potassium, and sodium. Surface ● The surface is heavily cratered. ● There are many scarps caused as cooling and shrinking of the core wrinkled the surface. ● The Caloris basin is a prominent impact crater 840 miles (1,350 km) wide. Composition ● Mercury has a relatively large iron core that composes 42 percent of the planet’s volume (Earth’s core composes just 17 percent of its volume). Orbit and rotation ● It spins on its axis three times for every two orbits of the Sun. ● It is not tidally locked to the Sun as originally thought. ● An observer on the surface would see the Sun in retrograde motion (moving backwards across the sky) for the period during which Mercury’s orbital velocity exceeds it rotational velocity. 40 iron-nickel core about 1,125 miles (1,800 km) thick makes up almost 80% of the planet’s mass rocky mantle about 375 miles (600 km) thick light surface crust a b c Mercury a b c Data Diameter 3,030 miles (4,880 km) Mean distance from Sun 36 million miles (58 million km) Average surface temperature –279 to +801°F (–173 to +427°C) Rotation period 59 days Sidereal period 88 days Comparative sizes of Mercury and Earth Mercury atmosphere axis core crust impact crater mantle orbit retrograde rotational period sidereal period tidally locked Key words © Diagram Visual Information Ltd.
THE SUN’S FAMILY Atmosphere ● Venus has a very dense atmosphere consisting of carbon dioxide and nitrogen. ● Atmospheric pressure at the surface is about 90 times that on Earth. ● The carbon dioxide-rich atmosphere produces a strong greenhouse effect. ● Dense clouds composed of sulfur dioxide and sulfuric acid droplets completely obscure the surface. Surface ● Most of the surface (90 percent) is composed of solidified lava and there are few craters. ● The dense atmosphere is thought to burn up all but the largest meteorites before they can impact the surface. ● The surface rock is young. Venus may undergo periodic resurfacing events caused by massive volcanic upwellings. ● The greenhouse effect produced by the atmosphere means that surface temperatures are greater than those on Mercury, though Venus is more than twice as distant from the Sun. ● Ishtar Terra and Aphrodite Terra are two continent-sized highlands. Orbit and rotation ● It has a very slow, retrograde rotation on its axis (rotates east to west). ● It always presents the same face to Earth when at its closest approach. Composition ● Venus’ composition is very similar to Earth. 41 Venus a b c Data Diameter 7,520 miles (12,100 km) Mean distance from Sun 67 million miles (108 million km) Average surface temperature 864°F (462°C) Rotation period 243 days Sidereal period 224.7 days partially-molten metallic core with a radius of 1,837 miles (2,940 km) mantle 1,906 miles (3,050 km) thick crust 37 miles (60 km) thick a b c Comparative sizes of Venus and Earth Venus atmosphere axis core crater crust greenhouse effect mantle meteorite orbit retrograde rotational period sidereal period Key words © Diagram Visual Information Ltd.
Earth THE SUN’S FAMILY atmosphere core crust greenhouse gas impact crater mantle rotational period sidereal period Key words 42 Earth solid metal inner core with a radius of 1,000 miles (1,600 km) molten outer core 1,140 miles (1,820 km) thick semi-molten rocky lower mantle 1,430 miles (2,290 km) thick upper mantle 390 miles (640 km) thick crust 6.25 to 25 miles (10–40 km) thick a a b c d e b c d e Data Diameter 7,930 miles (12,760 km) Mean distance from Sun 93 million miles (149.6 million km) Average surface temperature 57°F (14°C) Rotation period 23 hours 56 minutes Sidereal period 365.256 days Atmosphere ● Earth has a thick atmosphere composed of nitrogen, oxygen, argon, and traces of other gases. ● The composition of the atmosphere is significantly influenced by the presence of life on the planet. ● Greenhouse gases in the atmosphere produce warming that allows Earth to have liquid water on its surface. Surface ● Earth is the only planet known to have liquid water on its surface (covering about 70 percent of its total area). ● There are very few visible impact craters due to highly active erosion processes and frequent volcanic activity. ● Unlike any other planet the surface is composed of tectonic plates, which are in constant motion. Composition ● Earth is the densest planet in the solar system. ● It is composed of a large iron-rich core, a semi-molten iron and magnesium mantle, and a thin silicon-rich crust. © Diagram Visual Information Ltd.
THE SUN’S FAMILY Atmosphere ● A very thin atmosphere composed of gases vented from the Moon’s interior and particles of solar wind. Surface ● Flat plains, known as maria (seas; singular: mare), are the result of ancient lava flows that filled giant impact craters. ● Highlands, known as terrae, are very irregular mountainous regions created by the crowding together of large impact craters. ● Almost all maria are found on the side of the Moon facing Earth (the near side). ● Terrae dominate the far side of the Moon (the “dark side”). Composition ● The thickness of the crust is greater on the far side (60 miles, 100 km) than on the near side (37 miles, 60 km). ● The composition of the Moon is thought to be identical to Earth’s (though in different proportions). Orbit and rotation ● The Moon is tidally locked to Earth. ● The relative distances of the Moon and the Sun from Earth mean that the Moon appears to be the same size in the sky as the Sun. This is why total solar eclipses are possible. atmosphere core crust impact crater mantle mare rotational period sidereal period solar eclipse solar wind terrae tidally locked Key words 43 Earth a b c d Data Diameter 2,170 miles (3,475 km) Mean distance from Earth 235,177 miles (376,284 km) Average surface temperature –247 to 221°F (–155 to 105°C) Rotation period 27.321 days Sidereal period 27.231 days iron-rich core with a radius of 190 miles (300 km) partially-molten metal zone 220 miles (350 km) thick rigid mantle 600 miles (1,000 km) thick crust 45 miles (70 km) thick a b c d Comparative sizes of Earth and the Moon The Moon The Moon © Diagram Visual Information Ltd.
Earth’s tides Moon Earth’s orbital path The gravitational effect of the Moon on Earth’s surface waters: the Moon is overhead at the equator. S N equator Simple equilibrium model Tides new Moon, spring tide first-quarter, neap tide full Moon, spring tide third-quarter, neap tide Sun 1 2 4 3 Earth Moon tidal bulge (high tide) tidal trough (low tide) 1 2 3 4 THE SUN’S FAMILY Tides ● A tide is the regular rise and fall of the ocean’s surface. ● Bodies of water are influenced by the gravitational effects of the Moon and the Sun. ● In large bodies of water, such as the oceans, these effects become evident as tides. ● At any point in the ocean there are usually two high tides and two low tides each day. Simple equilibrium model ● A simplified model that assumes that Earth is covered by water at a uniform depth, and that the Moon remains directly above the equator, illustrates the Moon’s influence on Earth’s tides: ● The gravitational attraction of the Moon draws Earth’s water toward it, creating a bulge of water on the Moon side of Earth. ● On the opposite side of Earth the Moon’s gravitational attraction is correspondingly less, and an opposite bulge is formed. ● As Earth rotates every 24 hours, a point on the surface passes through the two bulges and the troughs in between them. These bulges are the high and low tides. ● In fact the Moon does not remain over the equator: its overhead position shifts between 28.5° N and 28.5° S, so the tidal bulges and troughs are rarely of equal size. ● Since the Moon advances in its orbit around Earth as Earth rotates, a full tidal cycle actually occurs every 24 hours and 50 minutes. equator full Moon gravitational attraction new Moon orbit tide Key words 44 © Diagram Visual Information Ltd.
THE SUN’S FAMILY Lunar phases ● Lunar phases refer to the regular cycle during which the appearance of the Moon changes as seen from Earth. ● Half of the Moon’s surface is constantly illuminated by the Sun (except during a lunar eclipse). ● As the illuminated portion is very bright compared to the non- illuminated portion, only the illuminated portion is visible to the naked eye from Earth. ● At different times, varying amounts of the illuminated portion of the Moon’s surface are visible from Earth. ● Lunar phases are a result of the constantly changing relative positions of Earth, the Moon, and the Sun. ● At times only a small crescent of the illuminated area of the Moon can be seen. At other times the entire illuminated area is facing Earth and is clearly visible. ● The amount of the illuminated area of the Moon that is visible increases until a full Moon is visible, and then decreases again until nothing of the Moon is visible. ● A full Moon is when the entire illuminated area is visible. ● A new Moon is when none of the illuminated area is visible. ● One lunar cycle, from new Moon to new Moon, takes 29.5 days. Lunar phases a b c d d c b a Sun’s light Earth Moon: half lit by Sun’s light as it orbits Earth appearance of the Moon as seen from Earth full Moon lunar cycle lunar eclipse lunar phase new Moon orbit Key words 45 © Diagram Visual Information Ltd.
annular solar eclipse central duration eclipse magnitude hybrid solar eclipse new Moon orbit partial solar eclipse perigee solar eclipse total solar eclipse THE SUN’S FAMILY Key words 46 Solar eclipse ● A solar eclipse occurs when the Moon passes in front of the Sun from the point of view of an observer. ● From the point of view of an observer on Earth, the Moon at perigee is slightly larger than the Sun in the sky. This means that the Moon can completely obscure the Sun. ● A partial solar eclipse is when only part of the Sun is obscured by the Moon. ● A total solar eclipse is when the entire Sun is obscured by the Moon. ● Observers may see a total solar eclipse, a partial solar eclipse, or no eclipse at all depending on their locations on Earth. ● An annular solar eclipse occurs when the Moon moves directly in front of the Sun and the Moon is at perigee. A thin ring of the Sun can still be seen around the Moon. ● A hybrid solar eclipse is when a total eclipse is visible from some locations on Earth and an annular eclipse is visible from other locations. ● Eclipse magnitude is a measure of how much of the Sun is covered by the Moon at the height of an eclipse. Any value greater than 1.0 is a total eclipse. ● Central duration is the length of time of the total or annular phase of an eclipse. ● A solar eclipse can only occur on the occasion of a new Moon. This is the only time when the Moon’s shadow can fall on Earth. Solar eclipses Total eclipse Partial eclipse Sun Moon total eclipse shadow misses Earth area of partial eclipse Sun Moon at perigee of orbit area of totality—sunlight is completely blocked by Moon area of partial eclipse—sunlight is partially blocked by Moon a b e d c a b d c g f e f g h h © Diagram Visual Information Ltd.
THE SUN’S FAMILY Lunar eclipse ● A lunar eclipse occurs when Earth passes between the Sun and the Moon and stops the Sun’s light from illuminating the Moon. In other words, when the Earth’s shadow falls on the Moon. ● A partial lunar eclipse is when Earth’s shadow obscures only part of the Moon. ● A total lunar eclipse is when Earth’s shadow obscures the whole Moon. ● Lunar eclipses can only occur when the Moon is full. This is the only time when Earth is positioned directly between the Moon and the Sun. ● Lunar eclipses do not occur at every full Moon because the Moon’s orbit around Earth is tipped by about five degrees from the plane of Earth’s orbit around the Sun. The Moon usually passes above or below Earth’s shadow. ● During a total lunar eclipse the Moon is not completely dark. Some light is refracted by Earth’s atmosphere and cast on the Moon. ● Umbral magnitude is the portion of the Moon’s visible surface obscured by Earth’s shadow. Values greater than 0 but less than 1 indicate a partial lunar eclipse. Values of 1 or greater indicate a total lunar eclipse. ● Total duration is the length of time that a total lunar eclipse persists. Lunar eclipses a b d c Sun Earth total shadow cast by Earth partial shadow cast by Earth Moon enters Earth’s partial shadow e f h i g g f h e i Partial eclipse Total eclipse Sun Earth total shadow cast by Earth Moon enters Earth’s total shadow a b d c full Moon lunar eclipse orbit partial lunar eclipse total duration total lunar eclipse umbral magnitude Key words 47 © Diagram Visual Information Ltd.
Lunar features THE SUN’S FAMILY Impact craters ● An impact crater is a depression in the surface of a celestial body formed by the impact of another body. ● Impact craters once completely covered the Moon’s surface before the formation of the lunar seas. ● Most of the Moon’s craters are believed to have been formed between three and four billion years ago. ● Craters located in the lunar seas are more recent. Seas ● A lunar sea, or mare, is a large, smooth, dark-colored area on the surface of the Moon. ● The lunar seas do not, and have never, contained water. ● They are flat areas created by huge lava flows in the Moon’s distant past. ● Lunar seas are only found on the side of the Moon facing Earth (the near side). impact crater lunar sea mare Key words 48 h a b i c d e f g h g b f c a e d Sea of Clouds (Mare Nubium) Sea of Tranquility (Mare Tranquilitatus) Sea of Storms (Oceanus Procellarum) Sea of Serenity (Mare Serenitatus) Sea of Showers (Mare Imbrium) Sea of Crises (Mare Crisium) Sea of Fertility (Mare Fecunditatis) Sea of Nectar (Mare Nectaris) a b c d e f g h Clavius Tycho Ptolemaeus Grimaldi Kepler Copernicus Plato Langrenus Theophilus a b c d e f g h i Impact craters Seas © Diagram Visual Information Ltd.
aerodynamic heating atmosphere impact crater meteor meteorite meteoroid micrometeoroid orbital velocity planet THE SUN’S FAMILY Key words 49 Meteoroids Meteorite a b c d e f Regular meteor showers Shower Date of peak activity Parent comet Meteor frequency (maximum no. per hour) 110 8 18 30 65 25 10 15 55 20 January 4 April 22 May 5 July 3 August 12 October 21 November 8 November 17 December 14 December 23 Quadrantids Lyrids Eta Aquarids Delta Aquarids Perseids Orionids Taurids Leonids Geminids Ursids unknown Thatcher Halley unknown Swift-Tuttle Halley Encke Temple-Tuttle Asteroid 3200 Phaeton Tuttle enters Earth’s atmospheric at 30 miles per second (50 kmps) friction with atmospheric gases heats surface to several thousand degrees Fahrenheit bright tail of vaporized material given off by heated meteorite meteorite slows and cools; bright tail fades by altitude of about 10–15 miles (16–24 km) meteorite free falls at about 150–200 miles per hour (240–320 kmph) cooled meteorite coated with “sooty” crust impacts ground a b d c e f Classification ● Meteoroid is a general term for a lump of material in space that is larger than a molecule but smaller than about 160 feet (50 m) in diameter. ● Micrometeoroid is a general term for a meteoroid that is between five microns and six inches (15 cm) in diameter. Meteors ● Meteor is a general term for a meteorite that enters the atmosphere of a planet (usually Earth) but is vaporized by aerodynamic heating before it reaches the surface. ● Meteorite is a general term for a meteoroid that enters the atmosphere of a planet (usually Earth) and impacts the surface. ● The vast majority of meteorites are slowed from their orbital speeds by the atmosphere and impact the surface traveling no faster than a rock dropped from a tall building. ● Very few meteorites are large enough to still be traveling at a significant percentage of their orbital velocities when they impact the surface. These large meteorites can create impact craters many miles in diameter. ● About 500 small meteorites reach Earth’s surface every year. ● Most fall in the ocean and very few of the rest land near inhabited areas. Meteor showers ● Meteors enter the atmosphere at an average rate of about six per hour. ● At certain regular times of the year large numbers of meteors enter the atmosphere. These are known as meteor showers. ● Meteor showers occur when Earth passes through trails of dust and debris left by comets or asteroids (known as parent comets). © Diagram Visual Information Ltd.
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On every bridge, crossing, and square, the party halted, and silence was commanded by the ruffling of the drums. The banners were waved, and when no sound was heard and the crowd held their peace, the grave voice of the municipal crier arose, reading the proclamation, and adding: "The country is in danger!" This last line was dreadful, and rang in all hearts. It was the shriek of the nation, of the motherland, of France. It was the parent calling on her offspring to help her. And ever and anon the guns kept thundering. On all the large open places platforms were run up for the voluntary enlistments. With the intoxication of patriotism, the men rushed to put their names down. Some were too old, but lied to be inscribed; some too young, but stood on tiptoe and swore they were full sixteen. Those who were accepted leaped to the ground, waving their enrollment papers, and cheering or singing the "Let it go on," and kissing the cannon's mouth. It was the betrothal of the French to war—this war of twenty odd years, which will result in the freedom of Europe, although it may not altogether be in our time. The excitement was so great that the Assembly was appalled by its own work; it sent men through the town to cry out: "Brothers, for the sake of the country, no rioting! The court wishes disorder as an excuse for taking the king out of the city, so give it no pretext. The king should stay among us." These dread sowers of words added in a deep voice: "He must be punished." They mentioned nobody by name, but all knew who was meant.
Every cannon-report had an echo in the heart of the palace. Those were the king's rooms where the queen and the rest of the family were gathered. They kept together all day, from feeling that their fate was decided this time, so grand and solemn. They did not separate until midnight, when the last cannon was fired. On the following night Mme. Campan was aroused; she had slept in the queen's bedroom since a fellow had been caught there with a knife, who might have been a murderer. "Is your majesty ill?" she asked, hearing a moan. "I am always in pain, Campan, but I trust to have it over soon now. Yes," and she held out her pale hand in the moonbeam, making it seem all the whiter, "in a month this same moonlight will see us free and disengaged from our chains." "Oh, you have accepted Lafayette's offers," said the lady, "and you will flee?" "Lafayette's help? Thank God, no," said the queen, with repugnance there was no mistaking; "no, but in a month, my nephew, Francis, will be in Paris." "Is your majesty quite sure?" asked the royal governess, alarmed. "Yes, all is settled," returned the sovereign; "alliance is made between Austria and Prussia, two powers who will march upon Paris in combination. We have the route of the French princes and their allied armies, and we can surely say that on such and such a day they will be here or there." "But do you not fear—" "Murder?" The queen finished the phrase. "I know that might befall; but they may hold us as hostages for their necks when vengeance impends. However, nothing venture, nothing win."
"And when do the allied sovereigns expect to be in Paris?" inquired Mme. Campan. "Between the fifteenth and twentieth of August," was the reply. "God grant it!" said the lady. But the prayer was not granted; or, if heard, Heaven sent France the succor she had not dreamed of—the Marseillaise Hymn of Liberty.
CHAPTER VII. THE MEN FROM MARSEILLES. We have said that Barbaroux had written to a friend in the south to send him five hundred men willing to die. Who was the man who could write such lines? and what influence had he over his friends? Charles Barbaroux was a very handsome young man of barely twenty-five, who was reproached for his beauty, and considered by Mme. Roland as frivolous and too generally amorous. On the contrary, he loved his country alone, or must have loved her best, for he died for her. Son of a hardy sea-faring man, he was a poet and orator when quite young—at the breaking out of trouble in his native town during the election of Mirabeau. He was then appointed secretary to the Marseilles town board. Riots at Arles drew him into them; but the seething caldron of Paris claimed him; the immense furnace which needed perfume, the huge crucible hissing for purest metal. He was Roland's correspondent at the south, and Mme. Roland had pictured from his regular, precise, and wise letters, a man of forty, with his head bald from much thinking, and his forehead wrinkled with vigils. The reality of her dream was a young man, gay, merry, light, fond of her sex, the type of the rich and brilliant generation flourishing in '92, to be cut down in '93. It was in this head, esteemed too frivolous by Mme. Roland, that the first thought of the tenth of August was conceived, perhaps. The storm was in the air, but the clouds were tossing about in all directions for Barbaroux to give them a direction and pile them up
over the Tuileries. When nobody had a settled plan, he wrote for five hundred determined men. The true ruler of France was the man who could write for such men and be sure of their coming. Rebecqui chose them himself out of the revolutionists who had fought in the last two years' popular affrays, in Avignon and the other fiery towns; they were used to blood; they did not know what fatigue was by name. On the appointed day they set out on the two hundred league tramp, as if it were a day's strolling. Why not? They were hardy seamen, rugged peasants, sunburned by the African simoom or the mountain gale, with hands callous from the spade or tough with tar. Wherever they passed along they were hailed as brigands. In a halt they received the words and music of Rouget de l'Isle's "Hymn to Liberty," sent as a viaticum by Barbaroux to shorten the road. The lips of the Marseilles men made it change in character, while the words were altered by their new emphasis. The song of brotherhood became one of death and extermination—forever "the Marseillaise." Barbaroux had planned to head with the Marseilles men some forty thousand volunteers Santerre was to have ready to meet them, overwhelm the City Hall and the House, and then storm the palace. But Santerre went to greet them with only two hundred men, not liking to let the strangers have the glory of such a rush. With ardent eyes, swart visages, and shrill voices, the little band strode through all Paris to the Champs Elysées, singing the thrilling song. They camped there, awaiting the banquet on the morrow. It took place, but some grenadiers were arrayed close to the spot, a Royalist guard set as a rampart between them and the palace.
They divined they were enemies, and commencing by insults, they went on to exchanging fisticuffs. At the first blood the Marseillaise shouted "To arms!" raided the stacks of muskets, and sent the grenadiers flying with their own bayonets. Luckily, they had the Tuileries at their backs and got over the draw-bridge, finding shelter in the royal apartments. There is a legend that the queen bound up the wounds of one soldier. The Federals numbered five thousand—Marseilles men, Bretons, and Dauphinois. They were a power, not from their number, but their faith. The spirit of the revolution was in them. They had fire-arms but no ammunition; they called for cartridges, but none were supplied. Two of them went to the mayor and demanded powder, or they would kill themselves in the office. Two municipal officers were on duty—Sergent, Danton's man, and Panis, Robespierre's. Sergent had artistic imagination and a French heart; he felt that the young men spoke with the voice of the country. "Look out, Panis," he said; "if these youths kill themselves, the blood will fall on our heads." "But if we deliver the powder without authorization, we risk our necks." "Never mind. I believe the time has come to risk our necks. In that case, everybody for himself," replied Sergent. "Here goes for mine; you can do as you like." He signed the delivery note, and Panis put his name to it. Things were easier now; when the Marseilles men had powder and shot they would not let themselves be butchered without hitting back.
As soon as they were armed, the Assembly received their petition, and allowed them to attend the session. The Assembly was in great fear, so much so as to debate whether it ought not to transfer the meetings to the country. For everybody stood in doubt, feeling the ground to quake underfoot and fearing to be swallowed. This wavering chafed the southerners. No little disheartened, Barbaroux talked of founding a republic in the south. He turned to Robespierre, to see if he would help to set the ball rolling. But the Incorruptible's conditions gave him suspicions, and he left him, saying: "We will no more have a dictator than a king."
CHAPTER VIII. THE FRIEND IN NEED. The very thing encouraging the Tuileries party was what awed the rebels. The palace had become a formidable fortress, with a dreadful garrison. During the night of the fourth of August, the Swiss battalions had been drawn from out of town into the palace. A few companies were left at Gaillon, where the king might take refuge. Three reliable leaders were beside the queen: Maillardet with his Switzers, Hervilly with the St. Louis Knights and the Constitutional Guard, and Mandat, who, as National Guard commander, promised twenty thousand devoted and resolute fighting men. On the evening of the eighth a man penetrated the fort; everybody knew him, so that he had no difficulty in passing to the queen's rooms, where they announced "Doctor Gilbert." "Ah, welcome, welcome, doctor!" said the royal lady, in a feverish voice, "I am happy to see you." He looked sharply at her, for on the whole of her face was such gladness and satisfaction that it made him shudder. He would sooner have seen her pale and disheartened. "I fear I have arrived too late," he said. "It is just the other way, doctor," she replied, with a smile, an expression her lips had almost forgotten how to make; "you come at
the right time, and you are welcome. You are going to see what I have long yearned to show you—a king really royal." "I am afraid, madame, that you are deceiving yourself," he returned, "and that you will exhibit rather the commandant of a fort." "Perhaps, Doctor Gilbert, we can never come to a closer understanding on the symbolical character of royalty than on other matters. For me a king is not solely a man who may say, 'I do not wish,' but one who can say, 'Thus I will.'" She alluded to the famous veto which led to this crisis. "Yes, madame," said Gilbert, "and for your majesty, a king is a ruler who takes revenge." "Who defends himself," she retorted; "for you know we are openly threatened, and are to be attacked by an armed force. We are assured that five hundred desperadoes from Marseilles, headed by one Barbaroux, took an oath on the ruins of the Bastile, not to go home until they had camped on the ruins of the Tuileries." "Indeed, I have heard something of the kind," remarked Gilbert. "Which only makes you laugh?" "It alarms me for the king and yourself, madame." "So that you come to propose that we should resign, and place ourselves at the mercy of Messieurs Barbaroux and his Marseilles bullies?" "I only wish the king could abdicate and guarantee, by the sacrifice of his crown, his life and yours, and the safety of your children." "Is this the advice you give us, doctor?" "It is; and I humbly beseech you to follow it."
"Monsieur Gilbert, let me say that you are not consistent in your opinions." "My opinions are always the same, madame. Devoted to king and country, I wished him to be in accord with the Constitution; from this desire springs the different pieces of counsel which I have submitted." "What is the one you fit to this juncture?" "One that you have never had such a good chance to follow. I say, get away." "Flee?" "Ah, you well know that it is possible, and never could be carried out with greater facility. You have nearly three thousand men in the palace." "Nearer five thousand," said the queen, with a smile of satisfaction, "with double to rise at the first signal we give." "You have no need to give a signal, which may be intercepted; the five thousand will suffice." "What do you think we ought to do with them?" "Set yourself in their midst, with the king and your august children; dash out when least expected; at a couple of leagues out, take to horse and ride into Normandy, to Gaillon, where you are looked for." "You mean, place ourselves under the thumb of General Lafayette?" "At least, he has proved that he is devoted to you." "No, sir, no! With my five thousand in hand, and as many more ready to come at the call, I like another course better—to crush this revolt once for all." "Oh, madame, how right he was who said you were doomed."
"Who was that, sir?" "A man whose name I dare not repeat to you; but he has spoken three times to you." "Silence!" said the queen, turning pale; "we will try to give the lie to this prophet of evil." "Madame, I am very much afraid that you are blinded." "You think that they will venture to attack us?" "The public spirit turns to this quarter." "And they reckon on walking in here as easily as they did in June?" "This is not a stronghold." "Nay; but if you will come with me, I will show you that we can hold out some time." With joy and pride she showed him all the defensive measures of the military engineers and the number of the garrison whom she believed faithful. "That is a comfort, madame," he said, "but it is not security." "You frown on everything, let me tell you, doctor." "Your majesty has taken me round where you like; will you let me take you to your own rooms, now?" "Willingly, doctor, for I am tired. Give me your arm." Gilbert bowed to have this high favor, most rarely granted by the sovereign, even to her intimate friends, especially since her misfortune. When they were in her sitting-room he dropped on one knee to her as she took a seat in an arm-chair.
"Madame," said he, "let me adjure you, in the name of your august husband, your dear ones, your own safety, to make use of the forces about you, to flee and not to fight." "Sir," was the reply, "since the fourteenth of July, I have been aspiring for the king to have his revenge; I believe the time has come. We will save royalty, or bury ourselves under the ruins of the Tuileries." "Can nothing turn you from this fatal resolve?" "Nothing." She held out her hand to him, half to help him to rise, half to send him away. He kissed her hand respectfully, and rising, said: "Will your majesty permit me to write a few lines which I regard as so urgent that I do not wish to delay one instant?" "Do so, sir," she said, pointing to a writing-table, where he sat down and wrote these lines: "My Lord,—Come! the queen is in danger of death, if a friend does not persuade her to flee, and I believe you are the only one who can have that influence over her." "May I ask whom you are writing to, without being too curious?" demanded the lady. "To the Count of Charny, madame," was Gilbert's reply. "And why do you apply to him?" "For him to obtain from your majesty what I fail to do." "Count Charny is too happy to think of his unfortunate friends; he will not come," said the queen. The door opened, and an usher appeared.
"The Right Honorable, the Count of Charny," he announced, "desiring to learn if he may present his respects to your majesty." The queen had been pale, and now became corpse-like, as she stammered some unintelligible words. "Let him enter," said Gilbert; "Heaven hath sent him." Charny appeared at the door in naval officer's uniform. "Oh, come in, sir; I was writing for you," said the physician, handing him the note. "Hearing of the danger her majesty was incurring, I came," said the nobleman, bowing. "Madame, for Heaven's sake, hear and heed what Count Charny says," said Gilbert; "his voice will be that of France." Respectfully saluting the lord and the royal lady, Gilbert went out, still cherishing a last hope.
CHAPTER IX. CHARNY ON GUARD. On the night of the ninth of August, the royal family supped as usual; nothing could disturb the king in his meals. But while Princess Elizabeth and Lady Lamballe wept and prayed, the queen prayed without weeping. The king withdrew to go to confession. At this time the doors opened, and Count Charny walked in, pale, but perfectly calm. "May I have speech with the king?" he asked, as he bowed. "At present I am the king," answered Marie Antoinette. Charny knew this as well as anybody, but he persisted. "You may go up to the king's rooms, count, but I protest that you will very much disturb him." "I understand; he is with Mayor Petion." "The king is with his ghostly counselor," replied the lady, with an indescribable expression. "Then I must make my report to your majesty as major-general of the castle," said the count. "Yes, if you will kindly do so." "I have the honor to set forth the effective strength of our forces. The heavy horse-guards, under Rulhieres and Verdiere, to the number of six hundred, are in battle array on the Louvre grand square; the Paris City foot-guards are barracked in the stables; a hundred and fifty are drawn from them to guard at Toulouse House,
at need, the Treasury and the discount and extra cash offices; the Paris Mounted Patrol, only thirty men, are posted in the princes' yard, at the foot of the king's back stairs; two hundred officers and men of the old Life Guards, a hundred young Royalists, as many noblemen, making some four hundred combatants, are in the Bull's- eye Hall and adjoining rooms; two or three hundred National Guards are scattered in the gardens and court-yards; and lastly, fifteen hundred Swiss, the backbone of resistance, are taking position under the grand vestibule and the staircases which they are charged to defend." "Do not all these measures set you at ease, my lord?" inquired the queen. "Nothing can set me at ease when your majesty's safety is at stake," returned the count. "Then your advice is still for flight?" "My advice, madame, is that you ought, with the king and the royal children, be in the midst of us." The queen shook her head. "Your majesty dislikes Lafayette? Be it so. But you have confidence in the Duke of Liancourt, who is in Rouen, in the house of an English gentleman of the name of Canning. The commander of the troops in that province has made them swear allegiance to the king; the Salis- Chamade Swiss regiment is echeloned across the road, and it may be relied on. All is still quiet. Let us get out over the swing-bridge, and reach the Etoille bars, where three hundred of the horse-guards await us. At Versailles, we can readily get together fifteen hundred noblemen. With four thousand, I answer for taking you wherever you like to go." "I thank you, Lord Charny. I appreciate the devotion which made you leave those dear to you, to offer your services to a foreigner."
"The queen is unjust toward me," replied Charny. "My sovereign's existence is always the most precious of all in my eyes, as duty is always the dearest of virtues." "Duty—yes, my lord," murmured the queen; "but I believe I understand my own when everybody is bent on doing theirs. It is to maintain royalty grand and noble, and to have it fall worthily, like the ancient gladiators, who studied how to die with grace." "Is this your majesty's last word?" "It is—above all, my last desire." Charny bowed, and as he met Mme. Campan by the door, he said to her: "Suggest to the princesses that they should put all their valuables in their pockets, as they may have to quit the palace without further warning." While the governess went to speak to the ladies, he returned to the queen, and said: "Madame, it is impossible that you should not have some hope beyond the reliance on material forces. Confide in me, for you will please bear in mind that at such a strait, I will have to give an account to the Maker and to man for what will have happened." "Well, my lord," said the queen, "an agent is to pay Petion two hundred thousand francs, and Danton fifty thousand, for which sums the latter is to stay at home and the other is to come to the palace." "Are you sure of the go-betweens?" "You said that Petion had come, which is something toward it." "Hardly enough; as I understood that he had to be sent for three times."
"The token is, in speaking to the king, he is to touch his right eyebrow with his forefinger—" "But if not arranged?" "He will be our prisoner, and I have given the most positive orders that he is not to be let quit the palace." The ringing of a bell was heard. "What is that?" inquired the queen. "The general alarm," rejoined Charny. The princesses rose in alarm. "What is the matter?" exclaimed the queen. "The tocsin is always the trumpet of rebellion." "Madame," said Charny, more affected by the sinister sound than the queen, "I had better go and learn whether the alarm means anything grave." "But we shall see you again?" asked she, quickly. "I came to take your majesty's orders, and I shall not leave you until you are out of danger." Bowing, he went out. The queen stood pensive for a space, murmuring: "I suppose we had better see if the king has got through confessing." While she was going out, Princess Elizabeth took some garments off a sofa in order to lie down with more comfort; from her fichu she removed a cornelian brooch, which she showed to Mme. Campan; the engraved stone had a bunch of lilies and the motto: "Forget offenses, forgive injuries." "I fear that this will have little influence over our enemies," she remarked; "but it ought not be the less dear to us."
As she was finishing the words, a gunshot was heard in the yard. The ladies screamed. "There goes the first shot," said Lady Elizabeth. "Alas! it will not be the last." Mayor Petion had come into the palace under the following circumstances. He arrived about half past ten. He was not made to wait, as had happened before, but was told that the king was ready to see him; but to arrive, he had to walk through a double row of Swiss guards, National Guards, and those volunteer royalists called Knights of the Dagger. Still, as they knew he had been sent for, they merely cast the epithets of "traitor" and "Judas" in his face as he went up the stairs. Petion smiled as he went in at the door of the room, for here the king had given him the lie on the twentieth of June; he was going to have ample revenge. The king was impatiently awaiting. "Ah! so you have come, Mayor Petion?" he said. "What is the good word from Paris?" Petion furnished the account of the state of matters—or, at least, an account. "Have you nothing more to tell me?" demanded the ruler. "No," replied Petion, wondering why the other stared at him. Louis watched for the signal that the mayor had accepted the bribe. It was clear that the king had been cheated; some swindler had pocketed the money. The queen came in as the question was put to Petion. "How does our friend stand?" she whispered. "He has not made any sign," rejoined the king.
"Then he is our prisoner," said she. "Can I retire?" inquired the mayor. "For God's sake, do not let him go!" interposed the queen. "Not yet, sir; I have something yet to say to you," responded the king, raising his voice. "Pray step into this closet." This implied to those in the inner room that Petion was intrusted to them, and was not to be allowed to go. Those in the room understood perfectly, and surrounded Petion, who felt that he was a prisoner. He was the thirtieth in a room where there was not elbow-room for four. "Why, gentlemen, we are smothering here," he said; "I propose a change of air." It was a sentiment all agreed with, and they followed him out of the first door he opened, and down into the walled-in garden, where he was as much confined as in the closet. To kill time, he picked up a pebble or two and tossed them over the walls. While he was playing thus, and chatting with Roederer, attorney of the province, the message came twice that the king wanted to see him. "No," replied Petion; "it is too hot quarters up there. I remember the closet, and I have no eagerness to be in it again. Besides, I have an appointment with somebody on the Feuillants' Quay." He went on playing at clearing the wall with stones. "With whom have you an appointment?" asked Roederer. At this instant the Assembly door on the Feuillants' Quay opened. "I fancy this is just what I was waiting for," remarked the mayor.
"Order to let Mayor Petion pass forth," said a voice; "the Assembly demands his presence at the bar of the House, to give an account of the state of the city." "Just the thing," muttered Petion. "Here I am," he replied, in a loud voice; "I am ready to respond to the quips of my enemies." The National Guards, imagining that Petion was to be berated, let him out. It was nearly three in the morning; the day was breaking. A singular thing, the aurora was the hue of blood.
CHAPTER X. BILLET AND PITOU. On being called by the king, Petion had foreseen that he might more easily get into the palace than out, so he went up to a hard-faced man marred by a scar on the brow. "Farmer Billet," said he, "what was your report about the House?" "That it would hold an all-night sitting." "Very good; and what did you say you saw on the New Bridge?" "Cannon and Guards, placed by order of Colonel Mandat." "And you also stated that a considerable force was collected under St. John's Arcade, near the opening of St. Antoine Street?" "Yes; again, by order of Colonel Mandat." "Well, will you listen to me? Here you have an order to Manuel and Danton to send back to barracks the troops at St. John's Arcade, and to remove the guns from the bridge; at any cost, you will understand, these orders must be obeyed." "I will hand it to Danton myself." "Good. You are living in St. Honore Street?" "Yes, mayor." "When you have given Danton the order, get home and snatch a bit of rest. About two o'clock, go out to the Feuillants' Quay, where you will stand by the wall. If you see or hear stones falling over from the other side of the wall, it will mean that I am a prisoner in the Tuileries, and detained by violence."
"I understand." "Present yourself at the bar of the House, and ask my colleagues to claim me. You understand, Farmer Billet, I am placing my life in your hands." "I will answer for it," replied the bluff farmer; "take it easy." Petion had therefore gone into the lion's den, relying on Billet's patriotism. The latter had spoken the more firmly, as Pitou had come to town. He dispatched the young peasant to Danton, with the word for him not to return without him. Lazy as the orator was, Pitou had a prevailing way, and he brought Danton with him. Danton had seen the cannon on the bridge, and the National Guards at the end of the popular quarter, and he understood the urgency of not leaving such forces on the rear of the people's army. With Petion's order in hand, he and Manuel sent the Guards away and removed the guns. This cleared the road for the Revolution. In the meantime, Billet and Pitou had gone to their old lodging in St. Honore Street, to which Pitou bobbed his head as to an old friend. The farmer sat down, and signified the young man was to do the same. "Thank you, but I am not tired," returned Pitou; but the other insisted, and he gave way. "Pitou, I sent for you to join me," said the farmer. "And you see I have not kept you waiting," retorted the National Guards captain, with his own frank smile, showing all his thirty-two teeth. "No. You must have guessed that something serious is afoot."
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  • 1. Space And Astronomy An Illustrated Guide To Science Science Visual Resources Diagram Group download https://ebookbell.com/product/space-and-astronomy-an-illustrated- guide-to-science-science-visual-resources-diagram-group-2217816 Explore and download more ebooks at ebookbell.com
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  • 6. SPACE AND ASTRONOMY SCIENCE VISUAL RESOURCES An Illustrated Guide to Science The Diagram Group
  • 7. Space and Astronomy: An Illustrated Guide to Science Copyright © 2006 The Diagram Group Editorial: Tim Furniss, Gordon Lee, Jamie Stokes Design: Anthony Atherton, Richard Hummerstone, Lee Lawrence, Trevor Mason, Roger Pring, Phil Richardson Illustration: Trevor Mason, Peter Wilkinson Picture research: Neil McKenna Indexer: Martin Hargreaves All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Chelsea House An imprint of Infobase Publishing 132 West 31st Street New York NY 10001 For Library of Congress Cataloging-in-Publication data, please contact the publisher. ISBN 0-8160-6168-8 Chelsea House books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at 212/967-8800 or 800/322-8755. You can find Chelsea House on the World Wide Web at http://www.chelseahouse.com Printed in China CP Diagram 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper.
  • 8. Introduction Space and Astronomy is one of eight volumes of the Science Visual Resources set. It contains eight sections, a comprehensive glossary, a Web site guide, and an index. Space and Astronomy is a learning tool for students and teachers. Full-color diagrams, graphs, charts, and maps on every page illustrate the essential elements of the subject, while parallel text provides key definitions and step-by-step explanations. The Universe provides an overview of the physical dimensions of space and current theories concerning its origin and eventual fate. This section also defines and illustrates the main classes of objects, from black holes to binary stars, that populate the known universe. The Sun’s Family examines our solar system and defines the various classes of celestial bodies that it includes. There are detailed comparisons of all nine planets as well as information about asteroids, meteoroids, planetary moons, and the Sun itself. Astronomy is concerned with the human effort to observe and understand objects beyond Earth from the earliest civilizations to the present day. It describes the different methods of astronomy that are used to examine the universe across the entire electromagnetic spectrum. Space Travel is an overview of the practical and theoretical challenges of getting into space and traveling through it. All aspects of space travel are covered, from the basics of celestial mechanics to the relative pros and cons of different types of propulsion. Uncrewed Exploration is a history of the exploration of space by uncrewed spacecraft. Crewed Exploration is a history of manned expeditions in space, from Yuri Gagarin to the contemporary crews of the International Space Station. The Space Shuttle and Using Space are concerned with the economic and scientific importance of space today. The many classes of satellite that provide the world with telecommunications and vital data are examined here.
  • 9. Contents 8 Size and scale 9 Distances 10 Beginnings of the universe 11 Endings of the universe 12 Bright stars 13 Close stars 14 Star pairs 15 Variable stars 16 Exoplanets 17 Stellar evolution 18 Stellar beginnings 19 Stellar birth 20 Regular star death 21 Large star death 22 Giant star death 23 Neutron stars 24 Black holes 25 Quasars 26 The Milky Way 27 Galaxy types 28 Galaxy groups 29 Hubble’s law 1 THE UNIVERSE 30 Beginnings of the solar system 31 Sizes 32 Distances 33 Temperatures 34 Orbits 35 Moons 36 Gravities 37 Planet summaries 38 Sunspots and flares 39 Solar wind 40 Mercury 41 Venus 42 Earth 43 The Moon 44 Earth’s tides 45 Lunar phases 46 Solar eclipses 47 Lunar eclipses 48 Lunar features 49 Meteoroids 50 Mars 51 Jupiter 52 Jupiter’s moons 53 Asteroids 54 Near Earth Objects 55 Saturn 56 Saturn’s rings 57 Uranus 58 Neptune 59 Pluto 60 Comets 61 Trans-Neptunian objects 62 Kuiper belt objects 63 Oort cloud objects 2 THE SUN’S FAMILY
  • 10. 64 Sky watching 65 Early astronomy 66 First astronomers 67 Renaissance astronomers 68 Electromagnetic spectrum 69 First telescopes 70 18th-century telescopes 71 Radio astronomy 72 Modern telescopes 73 Infrared astronomy 74 Ultraviolet astronomy 75 X-ray astronomy 76 Gamma ray astronomy 77 Cosmic ray astronomy 78 Sky map 79 Constellations 3 ASTRONOMY 80 Getting into orbit 81 Changing orbits 82 Getting to planets 83 Orbital inclination 84 Common Earth orbits 85 Uncommon Earth orbits 86 How rockets work 87 Liquid rocket fuel 88 Solid rocket fuel 89 Rocket stages 90 Rocket steering 91 Ion engines 92 Meeting in space 93 Walking in space 94 Returning to Earth 95 Space junk 4 SPACE TRAVEL 96 Early rockets 97 First western rockets 98 First eastern rockets 99 First military rockets 100 Sputnik 1 101 Sputnik 2 and 3 102 Explorer 1 103 Vanguard program 104 Explorer program 105 Discoverer and Corona 106 Telstar 1 107 Exploring the Sun 108 Exploring Mercury 109 Exploring Venus 110 Landing on Venus 111 Exploring the Moon 5 UNCREWED EXPLORATION
  • 11. 112 Landing on the Moon 113 Mars: early exploration 114 Mars: recent exploration 115 Mars: first landings 116 Mars: recent landings 117 Jupiter: early exploration 118 Jupiter: recent exploration 119 Saturn: early exploration 120 Saturn: recent exploration 121 Exploring Uranus and Neptune 122 Exploring asteroids 123 Exploring comets 124 Vostok 125 Mercury 126 Gemini 127 Voskhod 128 Soyuz 129 Apollo: overview 130 Apollo: getting there 131 Apollo: landing 132 Apollo: getting back 133 Apollo: Command Module 134 Apollo: Service Module 135 Apollo: Lunar Module 136 Apollo: Lunar Roving Vehicle 137 Apollo: Saturn V 138 Apollo: launch site 139 Apollo: landing sites 140 Apollo: science 141 Salyut 1–5 142 Salyut 6 and 7 143 Skylab 144 Mir 145 Mir parts 146 Shuttle-Mir 147 International Space Station 148 International Space Station: U.S./Russia 149 International Space Station: other countries 150 Shenzhou 151 Space travelers 6 CREWED EXPLORATION
  • 12. 198 Key words 205 Internet resources 207 Index APPENDIXES 152 Space Shuttle 153 Orbiter 154 Launch engines 155 Fuel tank 156 Flight path 157 Emergencies 158 Crew quarters 159 Space walking 160 Maneuvering 161 Heat protection 162 Hygiene 163 Robotic arm 164 Cargo 165 Cockpit flight controls 166 Food 167 Living 168 Working 169 Launching satellites 170 Launch 171 Landing 7 THE SPACE SHUTTLE 172 Television satellites 173 Multimedia satellites 174 Mobile communications satellites 175 Navigation satellites 176 Earth-watching satellites 177 Weather satellites 178 Environmental satellites 179 Atmospheric satellites 180 Radiation satellites 181 Data satellites 182 Earth observation satellites 183 Optical spy satellites 184 Radar spy satellites 185 Radio spy satellites 186 Early-warning satellites 187 Research satellites 188 Sun-watching satellites 189 Microgravity satellites 190 Radio astronomy 191 Infrared astronomy 192 Ultraviolet astronomy 193 X-ray astronomy 194 Gamma ray astronomy 195 Cosmic Background Explorer 196 Hubble Space Telescope 197 Launch totals 8 USING SPACE
  • 13. Size and scale ? 1,500,000 ly 150 million ly 15 billion ly 1,500 billion ly 0.015 ly 1.5 ly 150 ly 15,000 ly 3 4 7 8 5 6 1 2 THE UNIVERSE The universe ● The universe is the entirety of all matter, energy, and phenomena. ● The origins and ultimate fate of the universe are uncertain. Cubes of space ● Each cube has sides 100 times longer than the preceding cube. ● Each cube has a volume one million times greater than the preceding cube. 0.015 light years The solar system. 1.5 light years The Oort cloud. 150 light years The nearest stars to the Sun. 15,000 light years Part of a spiral arm of the Milky Way. 1,500,000 light years The Local Group of galaxies. 150 million light years The Local Supercluster of galaxies. 15 billion light years All known galaxies. 1,500 billion light years Unknown. galaxy galaxy group galaxy supercluster Local Group Local Supercluster Milky Way Oort cloud solar system star Key words 8 1 2 3 4 5 6 7 8 © Diagram Visual Information Ltd.
  • 14. Defining a parsec ● Earth (a) orbits the Sun (b) at a distance of 1 au. ● Over a period of about three months, Earth moves from position 1 to position 2. ● A nearby star (c) will change position against the background of more distant stars when observed from Earth at position 1 and then position 2. ● This change in angular position (p) is known as parallax. ● When a star’s parallax is exactly 1 arc second (1/3600 of a degree) that star is exactly one parsec distant from Earth. ● The distance in parsecs of any star that is close enough to have an observable parallax can be calculated from this relationship. THE UNIVERSE Measuring distances ● Astronomical distances are too large to be usefully measured in miles or kilometers. ● Astronomers use much larger units of measurement. Astronomical unit (au) ● An astronomical unit (au) is the mean distance between Earth and the Sun. ● It is used to describe distances within solar systems. Light year (ly) ● A light year (ly) is the distance traveled by light in a vacuum in one year. ● It is used to describe the distances between stars or the dimensions of galaxies. ● Terms such as light second, light day, or light month are also used to denote distances traveled by light in other time spans. Parsec (pc) ● Parsec (pc) is an abbreviation of “parallax second.” ● This denotes the distance at which a baseline of 1 au subtends an angle of 1 arc second. ● It is used to describe distances between galaxies. ● The terms kiloparsec (kpc) and megaparsec (Mpc) are also used to denote distances of 1,000 parsecs and one million parsecs respectively. Distances Astronomical distances 1 au 93 million miles (149.6 million km) 1 ly 5,878 trillion miles (9,460 trillion km) 1 parsec 19,174 trillion miles (30,857 trillion km) astronomical unit (au) kiloparsec (kpc) light day light month light second light year (ly) megaparsec (Mpc) parallax parsec (pc) solar system Key words 9 2 a b 1 c p Journey Apollo to the Moon Furthest flight Apollo to Voyager across (Pioneer 10) Proxima Centauri our galaxy Distance 238,328 miles 7 billion miles 4.2 ly 100,000 ly 383,551.7 km 384,400 km 11 billion km Time 3 days 30 years 900,000 years 1,904,760,000 yrs Traveling distance © Diagram Visual Information Ltd. 2 a b 1 c p Journey Apollo to the Moon Furthest flight Apollo to Voyager across (Pioneer 10) Proxima Centauri our galaxy Distance 238,328 miles 7 billion miles 4.2 ly 100,000 ly 383,551.7 km 384,400 km 11 billion km Time 3 days 30 years 900,000 years 1,904,760,000 yrs Traveling distance
  • 15. Big bang evidence THE UNIVERSE Big bang theory ● The view that the universe began at a single point in space and time at which all matter and energy came into existence is called the big bang theory. ● It arose in response to the discovery that the universe appears to be constantly expanding. ● A constantly expanding universe suggests that the expansion must have started at some point in the past. ● This point is referred to as the big bang. ● Hubble’s law allows astronomers to extrapolate backwards from the current size and rate of expansion of the universe to determine when the big bang must have occurred. ● The calculation can only be performed by determining a value for Hubble’s constant: the actual rate of expansion. ● Current estimates set the time of the big bang at about 13.7 billion years ago. Big bang concepts ● Matter did not expand out from the big bang into space over a period of time: space and time came into existence with the big bang and have been expanding ever since. ● The universe was very different in the past to what it is now, and will be very different in the future. ● The origins of the big bang itself are unknown. A theory of gravity on very small scales—quantum gravity—is needed to explain processes within the big bang. big bang cosmic microwave background radiation (CMB) element galaxy gravity Hubble’s constant Hubble’s law quantum gravity quasar Key words 10 Cosmic microwave background radiation ● In the early universe temperatures would have been so high that subatomic particles would have been too energetic to form atoms. This would have resulted in a universe opaque to light. ● Evidence for this period appears as cosmic microwave background radiation (CMB): a uniform background haze of radiation at about 2.725 kelvins. Abundance of elements ● The relative abundance of helium-4, helium-3, deuterium, and lithium-7 in the universe are very close to the levels predicted by the theory. ● No other theory attempts to explain why there should be, for example, more helium than deuterium. Quasars and galaxies ● The observable universe is more or less isotropic in space, but not in time. ● Objects at a great distance are seen as they were long ago in the past. Closer objects are seen as they were more recently. ● Different kinds of objects are more often seen at great distances than at close distances, suggesting that they evolved at various stages in the universe’s history when conditions were different. ● For example, no quasars have been observed close to Earth. Beyond a certain distance, many are seen. Beyond a greater distance, there are none. This suggests that quasars only evolved during a certain period. This in turn suggests that the universe is itself evolving. Expansion of space and time since the big bang Beginnings of the universe © Diagram Visual Information Ltd.
  • 16. THE UNIVERSE Fate of an expanding universe ● If the universe began with the big bang and is currently expanding, there are three possible future scenarios: Closed universe ● The gravitational attraction of all the matter in the universe may be high enough to slow the expansion and eventually reverse it. ● The universe will reach a maximum extent and then contract back to a singularity (the big crunch). Open universe ● If there is insufficient matter in the universe for gravity to slow its expansion, the universe will go on expanding forever. ● Entropy will ensure that, eventually, all star formation will stop, all matter will decay into dispersed subatomic particles, and black holes will evaporate. ● This ultimate conclusion of entropy is known as the heat death of the universe. Static universe ● If there is just enough matter in the universe to slow and eventually stop its expansion, but not enough to cause it to collapse again, the universe will reach a maximum extent and become static. ● In this scenario the universe will also eventually undergo a heat death. Endings of the universe big bang big crunch black hole closed universe dark matter entropy galaxy galaxy cluster galaxy supercluster gravitational attraction heat death MACHO missing mass open universe WIMP Key words 11 Dark matter ● In order to predict the fate of the universe accurately, astronomers must know how much matter it contains. ● The structure of galaxies, galaxy clusters, and galaxy superclusters cannot be explained without assuming that a large proportion of the matter they contain cannot be observed (the missing mass problem). ● This matter is known as dark matter and is thought to make up 90–95 percent of the mass of the universe. ● There are two explanations for what dark matter consists of: ● Massive Compact Halo Objects (MACHOs) are large dense pieces of baryonic matter such as brown dwarfs. ● Weakly Interacting Massive Particles (WIMPs) are elementary particles other than electrons, protons, and neutrons that have mass but interact only very rarely with other matter. ● Current theories suggest that dark matter consists of both MACHOs and WIMPs. Closed universe Open universe Static universe © Diagram Visual Information Ltd.
  • 17. Bright stars THE UNIVERSE Star magnitude ● Astronomers describe the brightness of a star as its magnitude. ● Apparent magnitude is a measure of how bright a star appears to be in the night sky. This does not distinguish between stars that appear bright because they are close and those that are intrinsically bright. ● Absolute magnitude is a measure of how bright a star would appear to be if it were ten parsecs (32.6 ly) away. This is a measure of a star’s intrinsic brightness. ● For example, Sirius is the brightest star in the sky and Canopus is the second-brightest. In fact Canopus is about 600 times more luminous than Sirius, but it is much farther away so it appears dimmer. ● Absolute magnitude is measured in two ways: if the distance to a star is known, its apparent magnitude can be scaled up or down to match a distance of ten parsecs. Alternatively a star’s luminosity can be estimated according to its spectral type. Magnitude scales ● Stars with lower magnitude measurements (apparent or absolute) are brighter than stars with higher magnitude measurements. ● A magnitude 1 star is brighter than a magnitude 2 star and a magnitude –1 star is brighter still. ● Both magnitude scales are logarithmic: each step in the scale represents a 2.512 multiple increase in brightness. This means that a star of magnitude 1 is 100 times brighter than a star of magnitude 5. absolute magnitude apparent magnitude constellation luminosity magnitude Northern Hemisphere spectral type star Key words 12 Northern Hemisphere sky Signpost to five of the brightest stars Constellation of Orion Betelgeuse Rigel Sirius Procyon Capella Apparent magnitude –1.44 –0.62 –0.01 –0.05 +0.03 +0.08 +0.18 +0.40 +0.45 +0.45 +0.61 +0.76 The 12 brightest stars in the sky Name Sirius Canopus Alpha Centauri Arcturus Vega Capella Rigel Procyon Betelgeuse Achernar Hadar Altair Constellation Canis major Carina Centaurus Boötes Lyra Auriga Orion Canis minor Orion Eridanus Centaurus Aquila Distance (light years) 8.6 313.0 4.39 37.0 25.0 42.0 773.0 11.4 427 144.0 525.0 16.8 Absolute magnitude +1.5 –5.5 +4.1 –0.3 +0.6 –0.5 –6.7 +2.7 –5.1 –2.8 –5.4 +2.2 e d b c f a a b c d e f © Diagram Visual Information Ltd.
  • 18. THE UNIVERSE Closest stars ● The Milky Way galaxy contains about 200 billion stars. ● About 100 stars lie within 20 light years of the Sun. ● About 30 stars lie within 12 light years of the Sun. ● The closest star, Proxima Centauri, is 4.24 light years from the Sun. Alpha Centauri system ● Proxima Centauri is a member of a triple star system with Alpha Centauri A and Alpha Centauri B, both 4.34 light years from the Sun. ● Proxima Centauri is the dimmest star of the system and is not visible to the naked eye. ● Alpha Centauri A and B are separated by a distance of about 23 au and are not discernible as individual bodies to the naked eye. ● Alpha Centauri A, also known as Rigil Kentaurus, is very similar to the Sun and is the fourth brightest star in the sky. Local space ● The nature and distribution of the stars within 12 light years of Earth allows some conclusions to be made about local space. ● Stars are on average about eight light years apart. ● More than 50 percent of them belong to multiple star systems. ● Most are dimmer than the Sun. Close stars apparent magnitude binary star system constellation galaxy magnitude Milky Way multiple star system Northern Hemisphere star Key words 13 Name 1 Proxima Centauri 2 Alpha Centauri 3 Barnard’s Star 4 Wolf 358 5 Lalande 21185 6 Luyten 726.8 7 Sirius 8 Ross 154 9 Ross 248 10 Epsilon Eridani Of the ten stars closest to Earth only two can be seen with the naked eye from the Northern Hemisphere: Sirius in the constellation Canis Major; Epsilon Eridani in the constellation Eridanus. The ten nearest stars Constellation Centaurus Centaurus Ophiuchus Leo Ursa Major Cetus Canis Major Sagittarius Andromeda Eridanus Apparent magnitude +11.1 –0.01 +9.5 +13.6 +7.7 +12.3 –1.44 +10.5 +12.2 +3.7 Distance (light years) 4.24 4.39 6.0 7.8 8.2 8.5 8.6 9.6 10.3 10.6 Visibility of the nearest stars a b b a © Diagram Visual Information Ltd.
  • 19. Binary stars ● A binary star system consists of two stars orbiting each other around a common center of mass. ● Three, four, or more stars may orbit each other in the same way. ● Astronomers estimate that about 50 percent of all stars are part of binary or multiple star systems. ● The closest star to the Sun, Proxima Centauri, is part of a triple star system. Binary star types ● Eclipsing binaries are binary systems in which, from the point of view of an observer, one star periodically passes in front of the other . ● Astrometric binaries are binary systems in which only one member of the system is bright enough to be observed. The existence of the other member is inferred by its gravitational effects. ● Contact binaries are binary systems in which both member stars fill their Roche lobes. Their upper atmospheres form a common envelope. ● Detached binaries are binary systems in which both member stars are within their Roche lobes and have no significant effect on each other’s evolution. ● Visual binaries are stars that appear to be members of a binary system from the point of view of an observer, but which are not actually gravitationally linked. ● X-ray binaries are binary systems that periodically emit powerful X-rays. This is thought to occur when one system member is a neutron star or a black hole with an accretion disc formed from material drawn from the other member. Star pairs THE UNIVERSE accretion disc astrometric binary binary star system black hole contact binary detached binary eclipsing binary Lagrange point multiple star system neutron star orbit Roche lobe star visual binary X-ray binary Key words 14 Roche lobe a b c d e Lagrange point The Mizar-Alcor multiple system Alcor (a) takes 10 million years to orbit Mizar (b). Mizar also has two, closer companions (c, d). Alcor also has a close companion (e). Binary system Visual binary Roche lobe © Diagram Visual Information Ltd. ● A Roche lobe is the region around a star in a binary system within which material is gravitationally bound to that star. ● The Roche lobes of two stars in a binary system are tear-shaped volumes of space with their apexes touching at the Lagrange point of the system. ● If a star expands so that some of its surface lies outside of its Roche lobe, that material may be drawn into the Roche lobe of its companion. ● The overflow of material from one Roche lobe into another is thought to be responsible for the formation of accretion discs.
  • 20. THE UNIVERSE Variable star ● A star that undergoes a great change in luminosity over a relatively short time period is a variable star. ● For comparison, the Sun varies in luminosity by about 0.1 percent over an 11 year cycle but is not considered to be a variable star. ● Some variable stars have regular cycles of variation, others are irregular. Intrinsic variables ● Stars that vary in luminosity because of features intrinsic to those stars are intrinsic variables. ● Mira variables are old, giant red stars. Their luminosity varies because they expand and contract over periods of 100 days or more. ● Cepheid variables are giant yellow stars. Their luminosity varies because they periodically expand and contract. ● Semiregular variables are giant or supergiant stars that have variations in luminosity that are usually regular but can be irregular. ● Irregular variables are stars that vary in luminosity irregularly. Extrinsic variables ● Extrinsic variables are stars that appear to vary in luminosity because of extrinsic factors. ● The most common are eclipsing binary stars in which luminosity is affected by one star passing in front of another. ● Less common are binary systems in which the luminosity of the members is affected by accretion discs and other interactions. Variable stars a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 a The star is bright as seen from Earth because its companion is on the “far side.” b The companion begins to move in front of the main star. c The companion is in front of the main star, causing its light to dim. 1 A white dwarf sucks material from a red giant. 2 Captured material is shed in an explosion. + 100 days = 24–32 days a b c 1 2 absolute magnitude accretion disc apparent magnitude Cepheid variable eclipsing binary extrinsic variable galaxy intrinsic variable irregular variable luminosity magnitude Mira variable parallax semiregular variable star variable star Key words 15 Cepheid variables Mira variable Cepheid variable Eclipsing binary ● Cepheid variables are a form of intrinsic variable star. ● They are very useful to astronomers because their period of luminosity variability closely correlates to their absolute luminosity. ● For example, a Cepheid variable with a luminosity period of three days has an absolute luminosity of about 800 Suns. A Cepheid variable with a luminosity period of 30 days has an absolute luminosity of 10,000 Suns. ● These correlations were initially calculated by observing relatively close Cepheid variables whose distances had already been calculated by other methods such as parallax observations. ● Understanding this correlation allows astronomers to determine the distance of a Cepheid variable based solely on its observed period of luminosity. This is done by calculating the distance that a star with a known absolute magnitude (determined by its period of luminosity) must be in order to have its apparent magnitude observed. ● Because Cepheid variables tend to be very bright stars, they are visible across great distances. By determining the distance to a Cepheid variable in another galaxy, astronomers are able to determine the approximate distance to that galaxy as a whole. © Diagram Visual Information Ltd.
  • 21. Exoplanets THE UNIVERSE Exoplanet ● Exoplanet means “extra-solar planet.” ● An extra-solar planet is a planet in orbit around a star other than the Sun. Finding exoplanets ● More than 130 exoplanets have been confirmed to date. ● None can be observed directly with current technology: they are too dim and distant. ● The first exoplanets were discovered in 1992. Three planets were detected in orbit around the millisecond pulsar PSR B 1257+12 at a distance of about 2,630 light years from Earth. ● Pulsar timing is the detection of irregularities in the pulse periods of pulsars caused by the gravitation effects of planets orbiting them. The first exoplanets were found using this method. ● Astrometery is the measurement of irregularities in the proper motion of stars caused by orbiting planets. Current technologies are not sensitive enough to make this method reliable. ● Doppler method is the measurement of irregularities in a star’s spectral lines caused by orbiting planets. It is best at locating close-orbit planets. ● Gravitational lensing is the detection of the lensing effect of a star and its planets on light from a distant star in the background. It relies on the correct alignment of Earth with the target star and the distant star. ● Transit method is the detection of a planet’s shadow when it passes in front of a star. It also relies on the correct alignment of Earth, star, and planet. astrometry Doppler method exoplanet gas giant gravitational lensing main sequence millisecond pulsar neutron star orbit planet pulsar pulsar timing spectral line star transit method Key words 16 Exoplanet observations ● The oldest exoplanet so far discovered is thought to be about 13 billion years old. That is more than twice the age of Earth and only about one billion years younger than the universe. ● Its existence challenges accepted theories of planet formation. ● Most of the exoplanets discovered so far are gas giants like Jupiter, but have orbits much closer to their stars than Jupiter’s is to the Sun. ● This also undermines assumptions about solar system formation. ● The observed dissimilarity between other solar systems and our own may be due to the limitations of current methods of detection since planets smaller than gas giants cannot yet be reliably detected. © Diagram Visual Information Ltd. Comparison of solar systems Earth’s solar system: gas giants distant from the Sun Newly-discovered solar systems: gas giants much closer to their stars
  • 22. Stellar evolution THE UNIVERSE Star color ● The variation in the observed color of stars is apparent even to the naked eye. ● Instruments are able to discern very small variations in color between stars. ● The color of a star is closely related to its temperature. Spectral types ● Stars are commonly classified according to their surface temperatures using the Morgan- Keenan spectral classification scheme. ● A mnemonic for the order of the spectral classes (O, B, A, F, G, K, M) is “Oh Be A Fine Girl, Kiss Me.” ● Within each class, stars are further classified with numbers from 0 to 9. For example, A0 denotes the hottest stars in the A class and A9 the coolest. Hertzsprung-Russell diagram ● Different versions of the H-R diagram can show the relationships between absolute magnitude, luminosity, star classification, and surface temperature. ● The majority of stars fall into a few regions of the graph. ● The main sequence is a diagonal spread of stars from the top left to the bottom right of the diagram. ● Stars appear at different points on the diagram at different stages of their life spans. Stellar evolution a b e c d Example Spica (a) Polaris (b) Capella (c) Aldebaran (d) Betelgeuse (e) Color of star Blue White Yellow Orange Red Temperature ºC 30,000–10,000 10,000–7,000 7,000–5,000 5,000–3,000 3,000 Spectral type O, B A, F G K M Luminosity 1,000,000 10,000 100 Sun = 1 0.01 0.0001 Temperature (°C) Sun white dwarfs supergiants giants main sequence Hertzsprung-Russell diagram blue white yellow orange red 20,000 10,000 7,000 6,000 5,000 3,000 absolute magnitude Hertzsprung- Russell diagram luminosity magnitude main sequence Morgan-Keenan classification protostar red giant spectral type star stellar evolution T-Tauri star white dwarf Key words 17 ● As a star evolves over time its position on a Hertzsprung-Russell diagram changes. ● A protostar is cool but very large, so it has a high luminosity. It appears in the top right corner of an H-R diagram. ● Once the star has evolved to become a T-Tauri star, it has contracted and become hotter. It appears very close to the main sequence. ● Once stability has been achieved by hydrogen burning, the star appears within the main sequence. ● Exactly where a star joins the main sequence will depend on its mass. ● More massive stars will be hotter and larger (and therefore more luminous) and will join the main sequence farther to the top left of an H-R diagram than less massive stars. The Sun is at this point in its life and appears near the middle of the main sequence. ● When hydrogen burning stops and helium burning begins, a star rapidly departs from the main sequence as it becomes larger (and therefore more luminous) but cooler. ● A star that reaches a new equilibrium as a red giant or red supergiant appears near the center top of an H-R diagram. ● When helium burning stops in a red giant, the star quickly shrinks in size (and therefore becomes less luminous) until it stabilizes as a white dwarf, which appears near the center bottom of the diagram. © Diagram Visual Information Ltd.
  • 23. Stellar beginnings THE UNIVERSE Gas cloud ● Most of the empty space in a galaxy actually contains very low concentrations of gas and dust. ● In some regions this concentration is higher: these “clouds” or nebulae are the birthplaces of stars. ● Most clouds are in a state of equilibrium. ● The equilibrium of some clouds may be disrupted by supernova shock waves or the close approach of another cloud or massive object. ● These disruptions may cause changes in the density of parts of the cloud so that gravity overcomes kinetic energy. ● As particles clump together, larger and larger concentrations are formed, which in turn attract more matter. Protostar ● As a cloud contracts, it increases in temperature. Gravitational energy is converted into thermal kinetic energy. ● At first, most of the thermal energy escapes as infrared radiation. ● As the contracting cloud becomes denser, it becomes increasingly opaque to infrared radiation and the rate of heating rises. ● If enough mass is present to raise temperatures to 15,000,000 kelvins, a plasma forms. ● As contraction continues and temperatures rise further, the nuclear fusion of hydrogen may occur. Brown dwarf ● If not enough mass is present to generate the temperatures needed for nuclear fusion, a brown dwarf results. ● Brown dwarfs typically have masses between 13 and 75 times the mass of Jupiter. ● Some astronomers believe that brown dwarfs may be the most common objects in our galaxy. brown dwarf galaxy gravitational attraction infrared nebula nuclear fusion plasma protostar star supernova Key words 18 Gas cloud Protostar Contracting gas cloud © Diagram Visual Information Ltd.
  • 24. THE UNIVERSE T-Tauri star ● If temperatures become high enough for the nuclear fusion of hydrogen nuclei to occur, a protostar becomes a T-Tauri star. ● T-Tauri stars are situated just above the main sequence on a Hertzsprung- Russell diagram. ● Their fusion processes are restricted to a small central core. ● The star is still contracting gravitationally and some material is still falling onto its surface from an accretion disc. ● Strong winds push some material away and the star may emit polar jets of energetic radiation. ● Equilibrium has not been achieved. Mature star ● Eventually, the outward pressure generated by nuclear fusion balances the inward pressure of gravitation and the star achieves a stable diameter. ● Equilibrium is achieved and the star is situated on the main sequence of an H-R diagram. Life span ● The stable phase of a star’s life is usually its longest. ● This is because the nuclear fusion of hydrogen into helium is the most efficient of the nuclear burning stages. ● The length of time that a star remains in the main sequence is closely related to its mass. ● More massive stars have shorter spans of stable maturity than less massive stars. Stellar birth accretion disc core Hertzsprung- Russell diagram main sequence mature star nuclear fusion polar jet protostar star T-Tauri star Key words 19 T-Tauri star Polar jets Mature star and disc of leftover material © Diagram Visual Information Ltd.
  • 25. Regular star death THE UNIVERSE Red giant ● Once all the hydrogen in a star has undergone nuclear fusion into helium, fusion processes stop. ● Without the outward pressure generated by fusion, the star undergoes rapid gravitational contraction. ● This contraction raises the temperature and density of the core until the nuclear fusion of helium nuclei becomes possible. ● The pressure generated by helium fusion forces the star to expand again. ● A new equilibrium is reached, leaving the star with a diameter 100–200 times greater than it was during the hydrogen burning phase. ● The surface temperature and overall density are lower, but the density of the core is higher. White dwarf ● Once all the helium in a red giant has been fused into carbon, fusion processes stop again. ● The star undergoes rapid gravitational contraction again. ● If the star has a mass of less than about 3.4 times the mass of the Sun, this contraction will not produce enough heat to initiate the fusion of carbon nuclei. ● The star’s outer layers (about 80 percent of its mass) are ejected to form a planetary nebula. ● The remaining mass (about 20 percent of its original mass) contracts to form a white dwarf. ● It is thought that white dwarfs eventually cease shining, and become black dwarfs. black dwarf core nuclear fusion planetary nebula red giant white dwarf Key words 20 Mature star Red giant Planetary nebula White dwarf Black dwarf © Diagram Visual Information Ltd.
  • 26. THE UNIVERSE Large star death 21 Red supergiant ● Massive stars evolve into stars burning helium in the same way as stars with masses similar to the mass of the Sun. ● They swell to sizes much greater than those achieved by Sun-like stars and are known as red supergiants. ● Their greater masses allow them to achieve temperatures at which carbon and other, heavier, elements undergo nuclear fusion. ● Helium is fused into carbon, carbon into oxygen, oxygen into silicon, and silicon into iron. ● Massive stars are likely to suffer a supernova explosion once sustained fusion can no longer take place. Chandrasekhar limit ● The Chandrasekhar limit describes the maximum sustainable mass of a white dwarf: about 1.44 times solar mass. ● This is the mass at which a body’s tendency to contract due to gravitation can no longer be balanced by degeneracy pressure. ● This limit defines whether the core of a star will collapse to become a white dwarf, a neutron star, or a black hole. ● It refers only to that portion of a star’s mass that undergoes gravitational collapse when fusion reactions stop. ● For example, a massive star may lose a large proportion of its mass in the form of a planetary nebula and the remaining mass may be below the Chandrasekhar limit. Type I and II supernovas ● Type II supernovas result from the gravitational collapse of massive stars. ● Type I supernovas result when a white dwarf in a binary star system acquires additional mass from another star in that system, which causes it to exceed its Chandrasekhar limit. ● Type I supernovas are many times more powerful than Type II supernovas. binary star system black hole core neutron star nuclear fusion red supergiant supernova white dwarf Key words Mature star Red supergiant Type II supernova Neutron star © Diagram Visual Information Ltd.
  • 27. Giant star death THE UNIVERSE Giant stars ● The most massive stars undergo the same stages of evolution as large stars. ● No star is thought to be large enough to enable the sustained nuclear fusion of iron to occur in its core. ● Giant stars are eventually torn apart in supernova explosions. Supernova ● At the point where no more fusion reactions are possible the core of a red supergiant undergoes a very rapid gravitational collapse. ● The core collapses to a diameter of about six miles (10 km) in a fraction of a second. ● Material from the outer envelope collapses more slowly and is thought to rebound from the collapsed core. ● This rebound is incredibly energetic and causes the envelope to be ripped apart and ejected in a supernova. ● A supernova may release more energy in a second than the Sun will produce in its entire 10 billion-year life span. ● The surviving core may be a neutron star or, if it is more massive, may collapse further to become a black hole. Supernova seeding ● Only massive stars form relatively heavy elements such as oxygen, silicon, and iron through the fusion of lighter, more abundant elements. ● When a supernova occurs, these heavy elements are ejected into interstellar space at high speeds. ● Planets such as Earth, and the living things that exist on it, are partly made up of these heavy elements. ● Without red supergiant fusion and the subsequent seeding of its fusion products, rocky planets and life may not be possible. black hole core neutron star nuclear fusion red supergiant star supernova Key words 22 Mature star Red supergiant Type II supernova Black hole © Diagram Visual Information Ltd.
  • 28. THE UNIVERSE Neutron star ● A neutron star is a small but extremely dense object composed almost entirely of neutrons. ● A neutron star may be only six miles (10 km) in diameter but have between 1.4 and three times the mass of the Sun. ● Neutron stars are thought to be the collapsed remnants of massive stars that have exploded in supernovas. Neutron star features ● Neutron stars rotate very rapidly. The most rapid have rotation periods of hundredths of a second and the slowest of 30 seconds. ● This rapid rotation is due to the conservation of angular momentum: the slow rotation of the original massive star speeds up as the object shrinks. ● Rotation periods very slowly become longer over time: younger neutron stars rotate more rapidly than older ones. Neutron star types ● Magnestars are neutron stars with magnetic fields that are at least 1,000 times more intense than Earth’s. Their magnetic fields become weaker over time. ● X-ray bursters are neutron stars that have accretion discs formed from material drawn from orbiting companion stars. Friction in the accretion disc results in the periodic emission of powerful X-ray bursts. Neutron stars accretion disc exoplanet gamma ray magnestar millisecond pulsar neutron star orbit pole pulsar supernova X-ray X-ray burster Key words 23 Pulsars ● Pulsars are neutron stars that emit a stream of X-rays and gamma rays from their poles. These are recorded as regular pulses whenever an observer is in line of sight of one of the poles. ● As with all neutron stars, a pulsar’s rate of rotation slows as time passes. As its rotation slows, the frequency of the pulses is also reduced. ● However, millisecond pulsars are very old pulsars (one billion years or more) with very high rotation rates (pulse periods of less than 25 milliseconds). ● Millisecond pulsars are thought to form when material from a companion star falls onto a pulsar, causing it to spin more and more rapidly. ● The first exoplanets to be discovered are in orbit around millisecond pulsars. Manhattan Island neutron star Size By comparing a neutron star with Manhattan Island on the same scale, the neutron star’s very small size can be visualized. A cubic centimeter of matter from a neutron star would weigh about as much as 3,500 fully-laden Saturn V rockets on Earth. Mass A neutron star is the result of the collapse of a giant star many millions of times larger in size. As a result of this compression, neutron stars are very dense. 12 Miles 6 0 © Diagram Visual Information Ltd.
  • 29. Cygnus X-1 An X-ray source known as Cygnus X-1 may be related to the presence of a black hole in orbit around the star Eta Cygni. a blue giant star Eta Cygni b proposed orbiting black hole c material drawn from Eta Cygni by the black hole’s gravitation d heated material gives off X-rays as it accelerates toward the black hole c b d a Black holes THE UNIVERSE Black holes ● A black hole is a region of space with a gravity field so strong that nothing, including light, can escape from it: it has an escape velocity greater than the speed of light. ● A black hole is thought to result from the gravitational collapse of a massive star at the end of its life. ● Black holes may also be created in the centers of young galaxies. Black hole features ● No matter or information can flow from the inside of a black hole to the outside universe. ● The event horizon is the “surface” of a black hole. It is the perimeter at which the escape velocity is exactly the speed of light. ● At the center of a black hole there is a singularity where gravity and escape velocity become infinite. ● Astronomers suspect there are two classes of black hole: stellar mass and supermassive. ● Stellar mass black holes have masses between four and 15 times the mass of the Sun. ● Supermassive black holes have masses many billions of times greater than the Sun. ● Supermassive black holes are thought to form at the centers of active galaxies. accretion disc active galaxy axis black hole blue shift escape velocity event horizon galaxy gravitational lensing pole red shift singularity star stellar mass black hole supermassive black hole X-ray Key words 24 Detecting black holes The evidence ● Only indirect evidence for black holes has been observed. ● Evidence for the existence of black holes comes from the observation of phenomena close to where a black hole might be. Accretion disc ● Matter falling toward a black hole, but still outside the event horizon, is thought to form a rapidly spinning accretion disc. ● Friction between different zones of the accretion disc is thought to cause the emission of large amounts of X-rays. ● Narrow jets of particles moving at close to the speed of light are thought to be emitted along the polar axis of an accretion disc. Red and blue shifts ● Material orbiting a black hole would be moving away from an observer for one half of its orbit and toward the same observer for the other half. ● Velocity and direction of motion can be ascertained by measuring the blue shift or red shift of its emissions. ● Material orbiting a supermassive black hole at very high speeds would exhibit a large red shift on one half of its orbit and a large blue shift on the other. Other evidence ● Stars that appear to be orbiting a region of space where no matter is visible may be orbiting black holes. ● Gravitational lensing may distort light from objects behind and far beyond a black hole. © Diagram Visual Information Ltd.
  • 30. THE UNIVERSE Quasars ● The word quasar is derived from “quasi-stellar radio source.” ● Quasars are also known as QSOs or quasi-stellar objects. ● They appear as bright blue point sources through an optical telescope. ● Some have strong radio emissions (they are “radio loud”) but most do not (they are “radio quiet”). Quasar features ● The emissions from all quasars exhibit very high red shifts, indicating that they are very distant and therefore receding at very high velocities. ● Despite their great distance, they are very bright. ● A typical quasar has the same luminosity as about 1,000 Milky Way galaxies. ● Quasar luminosities vary over time periods of months, weeks, days, or hours. ● These relatively short periods of variation in luminosity indicate that they are relatively small (no effect can propagate across an object faster than the speed of light). ● Taken together, these features indicate that quasars are about the size of the solar system, but emit as much energy as a thousand large galaxies. Quasar origins ● Quasars are thought to be the active cores of very ancient galaxies. ● Their energy is thought to be produced by the effects of supermassive black holes on matter surrounding them. Quasars c b a d e red shift blue shift a A distant star receding from Earth at high velocity. b Light waves emitted in front of the star are squashed closer together. c An observer aboard a craft in the path of the star sees a blue-shifted image of the star. d Light waves emitted behind the star are stretched further apart. e An observer on Earth sees a red-shifted image of the star. blue shift galaxy luminosity Milky Way quasar quasi-stellar object (QSO) radio loud radio quiet red shift solar system star supermassive black hole Key words 25 Red shift and blue shift ● Red shift is a phenomenon used by astronomers to determine the distance of objects. ● Light travels in waves and its color depends upon its wavelength. When an object, such as a star, moving at high velocity gives out light, the light waves ahead of it are squashed closer together and the light waves behind it are stretched further apart. ● Light with longer (stretched) wavelengths is redder. Light with shorter (squashed) wavelengths is bluer. ● Objects receding from an observer at high velocity appear to be redder than they actually are (called red shift). ● The faster an object is receding from Earth the larger its red shift. The faster an object is traveling the farther away it must be, if it is true that the universe is constantly expanding. c b a d e red shift blue shift a A distant star receding from Earth at high velocity. b Light waves emitted in front of the star are squashed closer together. c An observer aboard a craft in the path of the star sees a blue-shifted image of the star. d Light waves emitted behind the star are stretched further apart. e An observer on Earth sees a red-shifted image of the star. c b a d e red shift blue shift a A distant star receding from Earth at high velocity. b Light waves emitted in front of the star are squashed closer together. c An observer aboard a craft in the path of the star sees a blue-shifted image of the star. d Light waves emitted behind the star are stretched further apart. e An observer on Earth sees a red-shifted image of the star. c b a d e red shift blue shift c b a d e red shift blue shift © Diagram Visual Information Ltd.
  • 31. The Milky Way THE UNIVERSE black hole galactic center galactic plane galaxy globular cluster Local Arm Milky Way spiral galaxy supermassive black hole Key words 26 The Milky Way ● The Milky Way is visible as an irregular band of faint light across the night sky. ● This band is the arm of our galaxy in which the Sun is located. ● Astronomers refer to our galaxy as a whole as the Milky Way. Our galaxy ● Our galaxy is a spiral galaxy with four major arms. ● It is thought to be unusually large. ● It contains about 100 billion stars. ● The central bulge is densely populated with old red stars. ● The arms are mostly populated by young blue stars. ● A spherical halo of old dull stars surrounds the main disc. ● Clusters of old stars (between 10,000 and a million) known as globular clusters also surround the main disc. ● Some astronomers believe there may be a supermassive black hole at the galactic center. The Sun’s place ● The Sun is situated in one of the Milky Way’s spiral arms known as the Orion or Local Arm. ● It is about 28,000 light years from the galactic center and about 20 light years above the center of the galactic plane. Components of the Milky Way 1 A dense bulging center with a high concentration of stars. 2 A surrounding halo of stars. 3 Trailing arms with less concentration of stars. 4 Our Sun, about 30,000 ly from the center. 4 3 100,000 light years 2 1 2,000 light years © Diagram Visual Information Ltd.
  • 32. THE UNIVERSE Galaxy ● A galaxy is a collection of stars, gas, and dust bound together by gravity. ● The universe contains many billions of galaxies. ● They typically contain millions to hundreds of billions of stars. ● There are four main types: elliptical, spiral, barred spiral, and irregular. Elliptical galaxies ● Elliptical galaxies are the most common kind of galaxy. ● They have a smooth rounded appearance, without complex regular structural features. ● They contain little gas or dust. ● They contain few hot bright stars and many dull old stars. Spiral galaxies ● Spiral galaxies resemble a flattened disc with outlying spiral arms in the same plane. ● The central disc is dense and contains mainly older stars. ● The spiral arms contain gas, dust, and younger stars. ● They are surrounded by a halo of older stars and dense clusters of older stars. ● Our galaxy is a spiral galaxy. Barred spiral galaxies ● A barred spiral galaxy is a spiral galaxy in which the arms originate from the ends of a bar through the galactic core. Irregular galaxies ● Irregular galaxies have no regular shape or symmetrical features. ● Many contain a lot of gas, dust, and young stars. Galaxy types barred spiral galaxy elliptical galaxy galaxy gravity irregular galaxy spiral galaxy star Key words 27 NGC 1300 in Eridanus M 51: the Whirlpool galaxy Large Magellanic Cloud NGC 4472 in Virgo Elliptical galaxy Spiral galaxy Irregular galaxy Barred spiral galaxy © Diagram Visual Information Ltd.
  • 33. Galaxy groups THE UNIVERSE Clusters ● Galaxies are not randomly distributed in space. ● They are clumped together in groups, clusters, and superclusters. ● A group contains fewer than 50 galaxies and has a diameter of about two Megaparsecs (Mpc). ● A cluster contains 50–1,000 galaxies and has a diameter of about eight Mpc. ● A supercluster contains thousands of clusters and groups and may be millions of megaparsecs in extent. Voids, sheets, and filaments ● About 90 percent of space seems to consist of bubble-like voids in which very few galaxies are observed. ● Most voids are about 25 Mpc in diameter. The largest known, the Boötes void, has a diameter of about 124 Mpc. ● Galaxies are concentrated in sheets and filaments separated by these voids. ● Superclusters occur at the intersections of sheets and filaments. ● No structures larger than superclusters have been confirmed. Local group ● The Milky Way is a member of the Local Group of galaxies, which consists of about thirty other galaxies including the Andromeda galaxy and the Large and Small Magellanic Clouds. ● The Local Group is a member of the Virgo or Local Supercluster, which consists of about 100 other groups and clusters of galaxies, including the Virgo cluster. 28 Distribution of galaxies 1 million light years 1 billion light years © Diagram Visual Information Ltd. galaxy galaxy cluster galaxy group galaxy supercluster local group Local Supercluster Milky Way Key words
  • 34. THE UNIVERSE Hubble’s law ● U.S. astronomer Edwin Hubble (1889–1953) proved the existence of galaxies other than our own. ● He discovered that the universe is many times larger than previously thought. ● Red shift analysis showed that all objects outside our galaxy were receding. ● More distant objects were receding at greater velocities. ● He concluded that the universe is constantly expanding in all directions. ● Hubble’s law states: the further away an object is, the faster its rate of recession, and that this relationship is constant. Hubble’s constant ● Hubble’s constant is the actual ratio of the speed of recession of an object to its distance from the observer. Hubble’s law 29 Hubble’s constant The raisin cake analogy ● In an uncooked raisin cake (1) one raisin is chosen to represent Earth and the distances from it to other raisins in the cake are measured. ● After an hour, yeast in the cake has caused it to expand uniformly in all directions so that it is now twice the size (2). ● The distances between the “Earth” raisin and the other raisins are measured again and all distances are now twice what they were before. This means that more distant raisins have covered much larger distances relative to the “Earth” raisin than nearby raisins . They have covered this distance in the same time, so they are moving at a greater velocity than nearby raisins. 100,000 80,000 60,000 40,000 20,000 0 0 300 1,200 Distance Velocity 1,500 600 900 kma s–1 megaparsecs 1 2 a b c b b b c a a © Diagram Visual Information Ltd. galaxy Hubble’s constant Hubble’s law red shift Key words
  • 35. THE SUN’S FAMILY ecliptic gas giant inner planet orbit planet rocky planet solar system solar wind Key words 30 Beginnings of the solar system Observations ● A good theory of solar-system formation has to explain certain facts observed in our own solar system: ● In our own solar system the planets orbit very close to the plane of the ecliptic (the plane of Earth’s orbit around the Sun). ● All of the planets orbit around the Sun in the same direction. ● The inner planets are much smaller and have very different compositions to the outer gas giants. Modern theory ● The Sun was formed from a condensing cloud of gas and dust. ● As this cloud shrank, any rotation it had would have been accelerated by the conservation of angular momentum. ● This caused the cloud to flatten into a broad rotating disc. The planets are thought to have formed from material in the outer part of this disc. The Sun is thought to have formed from material in the inner part of the same disc. ● Temperatures were higher in the regions of the disc closer to the proto- Sun than they were in more distant regions. ● Higher temperatures and a strong solar wind would have driven lighter elements out of the inner solar system allowing only small dense planets to form. ● Lower temperatures farther away from the proto-Sun would allow lighter elements to clump together, resulting in large gaseous planets. a c Sun rocky planets frost line gaseous planets a b c d 0.3 au 3.5 au d b Temperature and formation of the solar system Two types of planet ● Within about 0.3 au of the Sun temperatures are too high for rocks, metals, or hydrogen compounds to exist as solids. No planets have been formed within this limit. ● Between about 0.3 au and 3.5 au of the Sun temperatures are low enough for rocks and metals to condense as solids, but too high for hydrogen compounds to do so. Rocky planets have formed within this band. ● Beyond about 3.5 au of the Sun (known as the “frost line”) temperatures are low enough for hydrogen compounds such as CO2 and H2O to condense as solids. Gaseous planets have formed beyond this limit. © Diagram Visual Information Ltd.
  • 36. THE SUN’S FAMILY Terrestrial planets ● The terrestrial planets, or rocky planets, are those similar in size and composition to Earth. ● They are smaller and denser than the Jovian planets. ● The terrestrial planets are Mercury, Venus, Earth, and Mars. ● They orbit closest to the Sun. Jovian planets ● The Jovian planets, or gas giants, are those similar in size and composition to Jupiter: Saturn, Uranus, and Neptune. ● They are larger and less dense than the terrestrial planets. ● They orbit farthest from the Sun. Trans-Neptunian objects ● A trans-Neptunian object is any object within the solar system with an orbit that is entirely or mostly beyond the orbit of Neptune. ● Pluto is classified as a trans-Neptunian object. Some astronomers believe that Pluto is too dissimilar to the other planets to be classified as a planet in its own right. ● Pluto is believed to consist mostly of ice and has a highly irregular orbit. ● Several other recently discovered bodies, including Sedna, Quaoar, and Varuna are similar in composition, size, and orbit to Pluto but are not regarded as planets. ● It is likely that, if Pluto were discovered today, it would not be classified as a planet. Sizes gas giant Jovian planet orbit rocky planet terrestrial planet trans-Neptunian object (TNO) Key words 31 Planet Diameter miles (km) Pluto 1,420 (2,280) Mercury 3,030 (4,879) Mars 4,220 (6,790) Venus 7,520 (12,100) Earth 7,930 (12,760) Planet Diameter miles (km) Neptune 30,780 (49,530) Uranus 31,760 (51,120) Saturn 74,900 (120,540) Jupiter 89,350 (142,980) a b c d e f g h i i a b c d e f g h © Diagram Visual Information Ltd.
  • 37. Distances THE SUN’S FAMILY Sun distances ● Each planet’s distance from the Sun varies because each has an elliptical orbit. ● Planetary distances are commonly given as their mean distances from the Sun during the course of an orbit. ● Pluto has the most eccentric orbit: for about 20 years of its 248-year orbits it is closer to the Sun than Neptune. Earth distances ● The distances between Earth and the other planets constantly change because the orbits of the planets are not synchronized. ● For example, when Venus is on the same side of the Sun as Earth it approaches Earth to within 26 million miles (42 million km), but when it is on the opposite side of the Sun it reaches a distance of about 160 million miles (258 million km). Distance visualization ● The inner planets are much more closely grouped together than the outer planets. ● The mean distance between Mars, the last of the inner planets, and Jupiter, the first of the outer planets, is three times greater than the space that spans the mean orbits of the inner planets combined. ● On average the mean distances between the orbits of the outer planets is about 22 times greater than the mean distances between the orbits of the inner planets. eccentricity inner planet outer planet orbit planet Key words 32 Mean distance from the Sun millions of miles (km) Neptune 2,790 (4,450) Uranus 1,780 (2,870) Saturn 886 (1,430) Mars 140 (230) Venus 67.2 (108) Mercury 36 (57.9) Earth 93 (150) Jupiter 483 (778) Mean distance from Earth millions of miles (km) Neptune 2,677 (4,308) Uranus 1,606 (2,585) Saturn 744 (1,197) Mercury 50 (80.5) Mars 35 (56.3) Venus 25 (40.2) Jupiter 367 (591) Pluto 2,670 (4,297) Pluto 3,700 (5,900) © Diagram Visual Information Ltd.
  • 38. THE SUN’S FAMILY Temperature ● The average temperature on the surface of a planet is determined by two main factors: ● The first factor is the distance from the Sun. The closer a planet’s orbit lies to the Sun, the more heat it receives. ● Atmospheric composition is the second factor. This determines how much of the Sun’s heat is retained. ● Earth and the Moon receive about the same amount of heat from the Sun. Since the Moon has no appreciable atmosphere however, very little of that heat is retained. ● Mercury is closer to the Sun than Venus, but average surface temperatures on Venus are higher than they are on Mercury because the composition of Venus’ atmosphere traps heat. Albedo ● Albedo is a measure of the reflectiveness of a planet or other celestial body. ● It is expressed as a percentage of the amount of sunlight that a body reflects back into space. ● Earth has an average albedo of about 38 percent. The Moon has an albedo of about 12 percent. ● Different regions have different albedos. A snow-covered landscape may have an albedo of 90 percent, but a deciduous forest only has about 13 percent. ● Albedo has a significant influence on surface temperatures. Temperatures albedo atmosphere orbit planet Key words 33 Masses of the planets Planet Mass Pluto 0.002 Mercury 0.06 Mars 0.11 Venus 0.82 Earth 1.0 Uranus 14.6 Neptune 17.2 Saturn 95.2 Jupiter 317.9 a b c d e f g h i Venus 864°F (462°C) Mercury –279° to +801°F (–173° to +427°C) Earth 57°F (14°C) Mars –225° to 63°F (–143° to 17°C) Jupiter –250°F (–157°C) Saturn –288°F (–178°C) Uranus –357°F (–216°C) Neptune –353°F (–214°C) Pluto –387° to –369°F (–233° to –223°C) Planet Average surface temperature °F (°C) a b c d e f g h i Surface temperatures of the planets Approximate Earth mass = 6,000,000,000,000,000,000,000 tons a b c d e f g h i b °C °F 900 800 700 600 500 400 300 200 100 0 –100 –200 –300 –400 450 400 350 300 250 200 150 100 0 50 –50 –100 –150 –200 c d e f g h i a © Diagram Visual Information Ltd.
  • 39. Orbits THE SUN’S FAMILY Describing orbits ● Rotational period is the time taken for a planet to complete one revolution on its axis (a local day). ● Sidereal period is the time taken for a planet to make one orbit of the Sun (a local year). ● Orbital speed is the average velocity at which a planet orbits the Sun. ● Eccentricity is a measure of how far an orbit departs from being a perfect circle (all planetary orbits are ellipses). ● Inclination is the angle between the plane of a planet’s orbit and a fixed reference plane (usually the plane of Earth’s orbit around the Sun, known as the ecliptic). Observations ● All the planets except Pluto orbit in planes very close to the ecliptic. ● All the planets orbit in the same direction around the Sun. ● Pluto has the largest eccentricity to its orbit. ● All the planets except Venus have rotational periods shorter than their sidereal periods (a local day is longer than a local year on Venus). axis eccentricity ecliptic inclination orbit orbital speed planet rotational period sidereal period Key words 34 Days (Earth) a b c d e f g h i Mercury 28.74 (46.24) Venus 21.0 (33.78) Earth 17.88 (28.77) Mars 14.46 (23.27) Jupiter 7.86 (12.65) Saturn 5.76 (9.27) Uranus 4.08 (6.56) Neptune 3.24 (5.21) Pluto 2.82 (4.54) Rotation periods Orbital speeds Sidereal periods Planet Miles per sec (km per sec) Planet Earath years Earth days Mercury 88.0 Venus 224.7 Earth 365.256 Mars 687.0 Jupiter 11.86 Saturn 29.46 Uranus 84.01 Neptune 164.80 Pluto 248.54 a b c d e f g h i Planet Mercury 59 Venus 243 Earth Mars Jupiter Saturn Uranus Neptune Pluto 6 Minutes Hours 0 0 23 24 9 10 17 16 0 0 0 56 37 55 39 8 7 0 Planetary orbits The yellow line indicates the distance traveled around the Sun in one Earth year. © Diagram Visual Information Ltd.
  • 40. THE SUN’S FAMILY Moon ● A moon is a natural satellite of a planet, although the natural companions of some non-planets (such as asteroids) may also be referred to as moons. ● There are more than 140 recognized moons in the solar system and more are continually being discovered. ● Mercury and Venus do not have moons. ● Earth has one large satellite (the Moon). Some astronomers refer to Earth and the Moon as a binary planet system because of the relatively large size of the Moon. ● Mars has two small irregularly shaped moons. ● The Jovian planets each have large numbers of moons. ● Pluto has one large and two much smaller moons. It is also considered to be part of a binary planet system by some astronomers because of the relative size of its largest moon, Charon. ● Theories of planet formation suggest that planets outside of the solar system, known as exoplanets, should also have moons, but none have yet been detected. Moon orbits ● All moons are tidally locked to the planets they orbit. ● No moons have moons of their own because the orbit that the moon of a moon would have to occupy would be inherently unstable. Moons asteroid binary planet system exoplanet Jovian planet moon orbit planet satellite solar system tidally locked Key words 35 Number of known moons Kahoolawe, Hawaii Deimos, Mars Moons can be larger than planets: Mercury is 3,030 miles (4,879 km) in diameter Pluto is 1,420 miles (2,280 km) in diameter Moon Of planet Diameter miles (km) Ganymede Jupiter 3,293 (5,270) Titan Saturn 3,200 (5,120) Callisto Jupiter 3,012 (4,820) Io Jupiter 2,286 (3,659) Europa Jupiter 1,906 (3,050) d e f g a b c Sizes of moons g f e d c a b g f e d c Island of Grenada Phobos, Mars a b a b c d e f g Planet Number of moons Earth 1 Mars 2 Jupiter 63 Saturn 49 Uranus 27 Neptune 13 Pluto 3 © Diagram Visual Information Ltd.
  • 41. Gravities THE SUN’S FAMILY Gravity ● Gravity is the tendency of masses to move toward each other. ● Gravitational attraction is the way in which this tendency is usually described. According to Albert Einstein’s generally accepted theory of gravity there is no such force as gravitational attraction, but the phrase is used when discussing the motion of celestial bodies and spacecraft. ● The gravitational attraction exerted by a body depends on its mass. More massive bodies exert greater gravitational attraction than less massive bodies. Planet gravities ● Because the planets have different masses, their gravitational attractions are also different. ● For example, it takes less energy to launch a spacecraft from the surface of Mars into orbit than it does to launch the same spacecraft from the surface of Earth. This is because Earth has a greater mass and therefore a greater gravitational attraction than Mars. gravitational attraction gravity orbit planet Key words 36 Planet Height Planetary high jumps An athelete capable of making a vertical jump of 3 feet (0.91 m) on Earth would achieve these heights on the other planets. Jupiter 1 foot 3.5 inches (0.39 m) Neptune 2 feet 6.5 inches (0.77 m) Uranus 2 feet 6.75 inches (0.78 m) Saturn 2 feet 7.25 inches (0.79 m) Venus 3 feet 4.75 inches (1.04 m) Mars 7 feet 10.75 inches (2.41 m) Mercury 8 feet 1.25 inches (2.47 m) Pluto Not known e f g h ? b c d e f g Planet Comparative gravity (Earth gravity = 1.0) Jupiter 2.64 Neptune 1.2 Uranus 1.17 Saturn 1.15 Planet Comparative gravity (Earth gravity = 1.0) Venus 0.88 Mars 0.38 Mercury 0.38 Pluto Not known a b c d e f g h e f g h d c b a Earth a b c d a © Diagram Visual Information Ltd.
  • 42. aphelion atmosphere axis equator greenhouse gas orbit perihelion pole rotational period sidereal period THE SUN’S FAMILY Key words 37 Planet summaries Pluto Neptune Uranus Mars Jupiter Saturn 74,900 miles (120,540 km) 886 million miles (1,430 million km) –288°F (–178°C) 10 hours 39 minutes 29.46 years Diameter Mean distance from Sun Surface temperature Rotation period Sidereal period 4,220 miles (6,790 km) 140 million miles (230 million km) –225° to +63°F (–143° to +17°C) 24 hours 37 minutes 687 days 89,350 miles (142,980 km) 483 million miles (778 million km) –250°F (–157°C) 9 hours 55 minutes 11.86 years 7,930 miles (12,760 km) 93 million miles (150 million km) 57°F (14°C) 23 hours 56 mins 365.26 days 3,030 miles (4,879 km) 36 million miles (57.9 million km) –279° to +801°F (–173° to +427°C) 59 days 88 days Diameter Mean distance from Sun Surface temperature Rotation period Sidereal period 7,520 miles (12,100 km) 67.2 million miles (108 million km) 864°F (462°C) 243 days 224.7 days 30,780 miles (49,530 km) 2,790 million miles (4,450 million km) –353°F (–214°C) 16 hours 7 minutes 164.80 years 1,420 miles (2,280 km) 3,700 million miles (5,900 million km) –387° to –369°F (–233° to 223°C) 6 days 248.54 years Diameter Mean distance from Sun Surface temperature Rotation period Sidereal period 31,760 miles (51,120 km) 1,780 million miles (2,870 million km) –357°F (–216°C) 17 hours 8 minutes 84.01 years Mercury Venus Earth © Diagram Visual Information Ltd. Diameter ● None of the planets in the solar system are perfect spheres. ● The equatorial diameters of all of the planets are slightly greater than their polar diameters. Mean distance from the Sun ● The orbits of all of the planets are elliptical. ● This means that there is a point on a planet’s orbit where it makes its closest approach to the Sun and a point where it is at its most distant. ● The closest point to the Sun is known as aphelion and the most distant point as perihelion. Surface temperature ● Planets closer to the Sun are generally warmer than planets farther away from the Sun, but the nature of a planet’s atmosphere has a great impact on surface temperature. ● For example, Venus has a very thick atmosphere laden with greenhouse gases, which gives it a very high and almost constant surface temperature. Mercury is much closer to the Sun but has a very thin atmosphere that does not trap heat. Consequently there is a great temperature difference between the side of Mercury facing the Sun and the side facing away from it. Rotational period ● A planet’s rotational period is the length of time it takes that planet to rotate once on its axis. This can be thought of as a local “day.” Sidereal period ● A planet’s sidereal period is the length of time it takes to complete one orbit around the Sun. This can be thought of as a local “year.” Not all planets have sidereal periods (years) that are longer than their rotational periods (days).
  • 43. Sunspots and flares THE SUN’S FAMILY Sunspots ● A sunspot is a region of the Sun’s surface that is cooler than its surroundings at about 8,500°F (4,700°C) rather than 10,300°F (5,700°C). ● They are darker because they are cooler. ● Sunspots are also slight depressions in the Sun’s surface. ● They are associated with magnetic fields surrounding the Sun. ● Different parts of the Sun’s surface rotate at different speeds, which results in lines of magnetic flux becoming twisted, with their ends puncturing the Sun’s surface. These puncture points are sunspots. ● Sunspots appear in pairs, each with opposite magnetic polarity, and fade after about two weeks. Solar flares ● A solar flare is a rapid and energetic eruption of material from the Sun’s surface. ● They are explosive events that typically last for no more than a few minutes. ● Solar flare strength is categorized as A, B, C, D, M, or X (with X being the most powerful). Each class is ten times more powerful than the preceding class. ● Increased solar flare activity corresponds with increased sunspot activity. ● The streams of energized particles emitted in a solar flare may interact with Earth’s atmosphere and cause interference with electronic and radio equipment. atmosphere solar flare sunspot Key words 38 Sunspot migration New sunspots aligned on the Sun’s surface. After time the Sun has revolved on its axis. Sunspots near the Sun’s equator have traveled a greater distance than those near the poles. Elements of a solar flare 1 2 1 2 Typical sunspot distribution a b c electromagnetic radiation a b electrons protons c © Diagram Visual Information Ltd.
  • 44. THE SUN’S FAMILY Solar wind ● Solar wind is the high-energy plasma constantly emitted into space from the surface of the Sun. ● It consists of a stream of ionized particles (mostly protons) with the same composition as the Sun’s corona. The volume of space influenced by the solar wind is known as the heliosphere. ● The heliopause is the boundary of the solar wind’s influence. ● The actual distance of the heliopause from the Sun is unknown. It certainly lies far beyond the orbit of Pluto. ● The position of the heliopause probably varies depending on the density of the local interstellar medium and the velocity of the wind. Solar prominences ● A solar prominence is a prominent structure of energetic material formed in the Sun’s chromosphere. ● An eruptive prominence is an arched structure following lines of magnetism that may persist for several hours. ● A quiescent prominence is a patch of energized gas that hangs in the Sun’s chromosphere for days. ● Prominences are associated with sunspots. Solar wind atmosphere chromosphere corona eruptive prominence galactic center heliopause heliosphere interstellar medium magnetosphere magnetotail orbit planet quiescent prominence solar prominence solar system solar wind sunspot Key words 39 Sun solar winds moving along lines of magnetism “bow shock” region where solar wind is deflected by the magnetosphere magnetosphere (Earth’s magnetic field) Earth distortion of the magnetosphere by solar wind creates a magnetotail interstellar gases and radiation deflected by heliosphere Solar wind eruptive prominence surface of the Sun sunspot group a b c Solar prominence a b c a b c e f g d a b c d e f g © Diagram Visual Information Ltd.
  • 45. THE SUN’S FAMILY Atmosphere ● Mercury has a trace atmosphere consisting of oxygen, potassium, and sodium. Surface ● The surface is heavily cratered. ● There are many scarps caused as cooling and shrinking of the core wrinkled the surface. ● The Caloris basin is a prominent impact crater 840 miles (1,350 km) wide. Composition ● Mercury has a relatively large iron core that composes 42 percent of the planet’s volume (Earth’s core composes just 17 percent of its volume). Orbit and rotation ● It spins on its axis three times for every two orbits of the Sun. ● It is not tidally locked to the Sun as originally thought. ● An observer on the surface would see the Sun in retrograde motion (moving backwards across the sky) for the period during which Mercury’s orbital velocity exceeds it rotational velocity. 40 iron-nickel core about 1,125 miles (1,800 km) thick makes up almost 80% of the planet’s mass rocky mantle about 375 miles (600 km) thick light surface crust a b c Mercury a b c Data Diameter 3,030 miles (4,880 km) Mean distance from Sun 36 million miles (58 million km) Average surface temperature –279 to +801°F (–173 to +427°C) Rotation period 59 days Sidereal period 88 days Comparative sizes of Mercury and Earth Mercury atmosphere axis core crust impact crater mantle orbit retrograde rotational period sidereal period tidally locked Key words © Diagram Visual Information Ltd.
  • 46. THE SUN’S FAMILY Atmosphere ● Venus has a very dense atmosphere consisting of carbon dioxide and nitrogen. ● Atmospheric pressure at the surface is about 90 times that on Earth. ● The carbon dioxide-rich atmosphere produces a strong greenhouse effect. ● Dense clouds composed of sulfur dioxide and sulfuric acid droplets completely obscure the surface. Surface ● Most of the surface (90 percent) is composed of solidified lava and there are few craters. ● The dense atmosphere is thought to burn up all but the largest meteorites before they can impact the surface. ● The surface rock is young. Venus may undergo periodic resurfacing events caused by massive volcanic upwellings. ● The greenhouse effect produced by the atmosphere means that surface temperatures are greater than those on Mercury, though Venus is more than twice as distant from the Sun. ● Ishtar Terra and Aphrodite Terra are two continent-sized highlands. Orbit and rotation ● It has a very slow, retrograde rotation on its axis (rotates east to west). ● It always presents the same face to Earth when at its closest approach. Composition ● Venus’ composition is very similar to Earth. 41 Venus a b c Data Diameter 7,520 miles (12,100 km) Mean distance from Sun 67 million miles (108 million km) Average surface temperature 864°F (462°C) Rotation period 243 days Sidereal period 224.7 days partially-molten metallic core with a radius of 1,837 miles (2,940 km) mantle 1,906 miles (3,050 km) thick crust 37 miles (60 km) thick a b c Comparative sizes of Venus and Earth Venus atmosphere axis core crater crust greenhouse effect mantle meteorite orbit retrograde rotational period sidereal period Key words © Diagram Visual Information Ltd.
  • 47. Earth THE SUN’S FAMILY atmosphere core crust greenhouse gas impact crater mantle rotational period sidereal period Key words 42 Earth solid metal inner core with a radius of 1,000 miles (1,600 km) molten outer core 1,140 miles (1,820 km) thick semi-molten rocky lower mantle 1,430 miles (2,290 km) thick upper mantle 390 miles (640 km) thick crust 6.25 to 25 miles (10–40 km) thick a a b c d e b c d e Data Diameter 7,930 miles (12,760 km) Mean distance from Sun 93 million miles (149.6 million km) Average surface temperature 57°F (14°C) Rotation period 23 hours 56 minutes Sidereal period 365.256 days Atmosphere ● Earth has a thick atmosphere composed of nitrogen, oxygen, argon, and traces of other gases. ● The composition of the atmosphere is significantly influenced by the presence of life on the planet. ● Greenhouse gases in the atmosphere produce warming that allows Earth to have liquid water on its surface. Surface ● Earth is the only planet known to have liquid water on its surface (covering about 70 percent of its total area). ● There are very few visible impact craters due to highly active erosion processes and frequent volcanic activity. ● Unlike any other planet the surface is composed of tectonic plates, which are in constant motion. Composition ● Earth is the densest planet in the solar system. ● It is composed of a large iron-rich core, a semi-molten iron and magnesium mantle, and a thin silicon-rich crust. © Diagram Visual Information Ltd.
  • 48. THE SUN’S FAMILY Atmosphere ● A very thin atmosphere composed of gases vented from the Moon’s interior and particles of solar wind. Surface ● Flat plains, known as maria (seas; singular: mare), are the result of ancient lava flows that filled giant impact craters. ● Highlands, known as terrae, are very irregular mountainous regions created by the crowding together of large impact craters. ● Almost all maria are found on the side of the Moon facing Earth (the near side). ● Terrae dominate the far side of the Moon (the “dark side”). Composition ● The thickness of the crust is greater on the far side (60 miles, 100 km) than on the near side (37 miles, 60 km). ● The composition of the Moon is thought to be identical to Earth’s (though in different proportions). Orbit and rotation ● The Moon is tidally locked to Earth. ● The relative distances of the Moon and the Sun from Earth mean that the Moon appears to be the same size in the sky as the Sun. This is why total solar eclipses are possible. atmosphere core crust impact crater mantle mare rotational period sidereal period solar eclipse solar wind terrae tidally locked Key words 43 Earth a b c d Data Diameter 2,170 miles (3,475 km) Mean distance from Earth 235,177 miles (376,284 km) Average surface temperature –247 to 221°F (–155 to 105°C) Rotation period 27.321 days Sidereal period 27.231 days iron-rich core with a radius of 190 miles (300 km) partially-molten metal zone 220 miles (350 km) thick rigid mantle 600 miles (1,000 km) thick crust 45 miles (70 km) thick a b c d Comparative sizes of Earth and the Moon The Moon The Moon © Diagram Visual Information Ltd.
  • 49. Earth’s tides Moon Earth’s orbital path The gravitational effect of the Moon on Earth’s surface waters: the Moon is overhead at the equator. S N equator Simple equilibrium model Tides new Moon, spring tide first-quarter, neap tide full Moon, spring tide third-quarter, neap tide Sun 1 2 4 3 Earth Moon tidal bulge (high tide) tidal trough (low tide) 1 2 3 4 THE SUN’S FAMILY Tides ● A tide is the regular rise and fall of the ocean’s surface. ● Bodies of water are influenced by the gravitational effects of the Moon and the Sun. ● In large bodies of water, such as the oceans, these effects become evident as tides. ● At any point in the ocean there are usually two high tides and two low tides each day. Simple equilibrium model ● A simplified model that assumes that Earth is covered by water at a uniform depth, and that the Moon remains directly above the equator, illustrates the Moon’s influence on Earth’s tides: ● The gravitational attraction of the Moon draws Earth’s water toward it, creating a bulge of water on the Moon side of Earth. ● On the opposite side of Earth the Moon’s gravitational attraction is correspondingly less, and an opposite bulge is formed. ● As Earth rotates every 24 hours, a point on the surface passes through the two bulges and the troughs in between them. These bulges are the high and low tides. ● In fact the Moon does not remain over the equator: its overhead position shifts between 28.5° N and 28.5° S, so the tidal bulges and troughs are rarely of equal size. ● Since the Moon advances in its orbit around Earth as Earth rotates, a full tidal cycle actually occurs every 24 hours and 50 minutes. equator full Moon gravitational attraction new Moon orbit tide Key words 44 © Diagram Visual Information Ltd.
  • 50. THE SUN’S FAMILY Lunar phases ● Lunar phases refer to the regular cycle during which the appearance of the Moon changes as seen from Earth. ● Half of the Moon’s surface is constantly illuminated by the Sun (except during a lunar eclipse). ● As the illuminated portion is very bright compared to the non- illuminated portion, only the illuminated portion is visible to the naked eye from Earth. ● At different times, varying amounts of the illuminated portion of the Moon’s surface are visible from Earth. ● Lunar phases are a result of the constantly changing relative positions of Earth, the Moon, and the Sun. ● At times only a small crescent of the illuminated area of the Moon can be seen. At other times the entire illuminated area is facing Earth and is clearly visible. ● The amount of the illuminated area of the Moon that is visible increases until a full Moon is visible, and then decreases again until nothing of the Moon is visible. ● A full Moon is when the entire illuminated area is visible. ● A new Moon is when none of the illuminated area is visible. ● One lunar cycle, from new Moon to new Moon, takes 29.5 days. Lunar phases a b c d d c b a Sun’s light Earth Moon: half lit by Sun’s light as it orbits Earth appearance of the Moon as seen from Earth full Moon lunar cycle lunar eclipse lunar phase new Moon orbit Key words 45 © Diagram Visual Information Ltd.
  • 51. annular solar eclipse central duration eclipse magnitude hybrid solar eclipse new Moon orbit partial solar eclipse perigee solar eclipse total solar eclipse THE SUN’S FAMILY Key words 46 Solar eclipse ● A solar eclipse occurs when the Moon passes in front of the Sun from the point of view of an observer. ● From the point of view of an observer on Earth, the Moon at perigee is slightly larger than the Sun in the sky. This means that the Moon can completely obscure the Sun. ● A partial solar eclipse is when only part of the Sun is obscured by the Moon. ● A total solar eclipse is when the entire Sun is obscured by the Moon. ● Observers may see a total solar eclipse, a partial solar eclipse, or no eclipse at all depending on their locations on Earth. ● An annular solar eclipse occurs when the Moon moves directly in front of the Sun and the Moon is at perigee. A thin ring of the Sun can still be seen around the Moon. ● A hybrid solar eclipse is when a total eclipse is visible from some locations on Earth and an annular eclipse is visible from other locations. ● Eclipse magnitude is a measure of how much of the Sun is covered by the Moon at the height of an eclipse. Any value greater than 1.0 is a total eclipse. ● Central duration is the length of time of the total or annular phase of an eclipse. ● A solar eclipse can only occur on the occasion of a new Moon. This is the only time when the Moon’s shadow can fall on Earth. Solar eclipses Total eclipse Partial eclipse Sun Moon total eclipse shadow misses Earth area of partial eclipse Sun Moon at perigee of orbit area of totality—sunlight is completely blocked by Moon area of partial eclipse—sunlight is partially blocked by Moon a b e d c a b d c g f e f g h h © Diagram Visual Information Ltd.
  • 52. THE SUN’S FAMILY Lunar eclipse ● A lunar eclipse occurs when Earth passes between the Sun and the Moon and stops the Sun’s light from illuminating the Moon. In other words, when the Earth’s shadow falls on the Moon. ● A partial lunar eclipse is when Earth’s shadow obscures only part of the Moon. ● A total lunar eclipse is when Earth’s shadow obscures the whole Moon. ● Lunar eclipses can only occur when the Moon is full. This is the only time when Earth is positioned directly between the Moon and the Sun. ● Lunar eclipses do not occur at every full Moon because the Moon’s orbit around Earth is tipped by about five degrees from the plane of Earth’s orbit around the Sun. The Moon usually passes above or below Earth’s shadow. ● During a total lunar eclipse the Moon is not completely dark. Some light is refracted by Earth’s atmosphere and cast on the Moon. ● Umbral magnitude is the portion of the Moon’s visible surface obscured by Earth’s shadow. Values greater than 0 but less than 1 indicate a partial lunar eclipse. Values of 1 or greater indicate a total lunar eclipse. ● Total duration is the length of time that a total lunar eclipse persists. Lunar eclipses a b d c Sun Earth total shadow cast by Earth partial shadow cast by Earth Moon enters Earth’s partial shadow e f h i g g f h e i Partial eclipse Total eclipse Sun Earth total shadow cast by Earth Moon enters Earth’s total shadow a b d c full Moon lunar eclipse orbit partial lunar eclipse total duration total lunar eclipse umbral magnitude Key words 47 © Diagram Visual Information Ltd.
  • 53. Lunar features THE SUN’S FAMILY Impact craters ● An impact crater is a depression in the surface of a celestial body formed by the impact of another body. ● Impact craters once completely covered the Moon’s surface before the formation of the lunar seas. ● Most of the Moon’s craters are believed to have been formed between three and four billion years ago. ● Craters located in the lunar seas are more recent. Seas ● A lunar sea, or mare, is a large, smooth, dark-colored area on the surface of the Moon. ● The lunar seas do not, and have never, contained water. ● They are flat areas created by huge lava flows in the Moon’s distant past. ● Lunar seas are only found on the side of the Moon facing Earth (the near side). impact crater lunar sea mare Key words 48 h a b i c d e f g h g b f c a e d Sea of Clouds (Mare Nubium) Sea of Tranquility (Mare Tranquilitatus) Sea of Storms (Oceanus Procellarum) Sea of Serenity (Mare Serenitatus) Sea of Showers (Mare Imbrium) Sea of Crises (Mare Crisium) Sea of Fertility (Mare Fecunditatis) Sea of Nectar (Mare Nectaris) a b c d e f g h Clavius Tycho Ptolemaeus Grimaldi Kepler Copernicus Plato Langrenus Theophilus a b c d e f g h i Impact craters Seas © Diagram Visual Information Ltd.
  • 54. aerodynamic heating atmosphere impact crater meteor meteorite meteoroid micrometeoroid orbital velocity planet THE SUN’S FAMILY Key words 49 Meteoroids Meteorite a b c d e f Regular meteor showers Shower Date of peak activity Parent comet Meteor frequency (maximum no. per hour) 110 8 18 30 65 25 10 15 55 20 January 4 April 22 May 5 July 3 August 12 October 21 November 8 November 17 December 14 December 23 Quadrantids Lyrids Eta Aquarids Delta Aquarids Perseids Orionids Taurids Leonids Geminids Ursids unknown Thatcher Halley unknown Swift-Tuttle Halley Encke Temple-Tuttle Asteroid 3200 Phaeton Tuttle enters Earth’s atmospheric at 30 miles per second (50 kmps) friction with atmospheric gases heats surface to several thousand degrees Fahrenheit bright tail of vaporized material given off by heated meteorite meteorite slows and cools; bright tail fades by altitude of about 10–15 miles (16–24 km) meteorite free falls at about 150–200 miles per hour (240–320 kmph) cooled meteorite coated with “sooty” crust impacts ground a b d c e f Classification ● Meteoroid is a general term for a lump of material in space that is larger than a molecule but smaller than about 160 feet (50 m) in diameter. ● Micrometeoroid is a general term for a meteoroid that is between five microns and six inches (15 cm) in diameter. Meteors ● Meteor is a general term for a meteorite that enters the atmosphere of a planet (usually Earth) but is vaporized by aerodynamic heating before it reaches the surface. ● Meteorite is a general term for a meteoroid that enters the atmosphere of a planet (usually Earth) and impacts the surface. ● The vast majority of meteorites are slowed from their orbital speeds by the atmosphere and impact the surface traveling no faster than a rock dropped from a tall building. ● Very few meteorites are large enough to still be traveling at a significant percentage of their orbital velocities when they impact the surface. These large meteorites can create impact craters many miles in diameter. ● About 500 small meteorites reach Earth’s surface every year. ● Most fall in the ocean and very few of the rest land near inhabited areas. Meteor showers ● Meteors enter the atmosphere at an average rate of about six per hour. ● At certain regular times of the year large numbers of meteors enter the atmosphere. These are known as meteor showers. ● Meteor showers occur when Earth passes through trails of dust and debris left by comets or asteroids (known as parent comets). © Diagram Visual Information Ltd.
  • 55. Exploring the Variety of Random Documents with Different Content
  • 56. On every bridge, crossing, and square, the party halted, and silence was commanded by the ruffling of the drums. The banners were waved, and when no sound was heard and the crowd held their peace, the grave voice of the municipal crier arose, reading the proclamation, and adding: "The country is in danger!" This last line was dreadful, and rang in all hearts. It was the shriek of the nation, of the motherland, of France. It was the parent calling on her offspring to help her. And ever and anon the guns kept thundering. On all the large open places platforms were run up for the voluntary enlistments. With the intoxication of patriotism, the men rushed to put their names down. Some were too old, but lied to be inscribed; some too young, but stood on tiptoe and swore they were full sixteen. Those who were accepted leaped to the ground, waving their enrollment papers, and cheering or singing the "Let it go on," and kissing the cannon's mouth. It was the betrothal of the French to war—this war of twenty odd years, which will result in the freedom of Europe, although it may not altogether be in our time. The excitement was so great that the Assembly was appalled by its own work; it sent men through the town to cry out: "Brothers, for the sake of the country, no rioting! The court wishes disorder as an excuse for taking the king out of the city, so give it no pretext. The king should stay among us." These dread sowers of words added in a deep voice: "He must be punished." They mentioned nobody by name, but all knew who was meant.
  • 57. Every cannon-report had an echo in the heart of the palace. Those were the king's rooms where the queen and the rest of the family were gathered. They kept together all day, from feeling that their fate was decided this time, so grand and solemn. They did not separate until midnight, when the last cannon was fired. On the following night Mme. Campan was aroused; she had slept in the queen's bedroom since a fellow had been caught there with a knife, who might have been a murderer. "Is your majesty ill?" she asked, hearing a moan. "I am always in pain, Campan, but I trust to have it over soon now. Yes," and she held out her pale hand in the moonbeam, making it seem all the whiter, "in a month this same moonlight will see us free and disengaged from our chains." "Oh, you have accepted Lafayette's offers," said the lady, "and you will flee?" "Lafayette's help? Thank God, no," said the queen, with repugnance there was no mistaking; "no, but in a month, my nephew, Francis, will be in Paris." "Is your majesty quite sure?" asked the royal governess, alarmed. "Yes, all is settled," returned the sovereign; "alliance is made between Austria and Prussia, two powers who will march upon Paris in combination. We have the route of the French princes and their allied armies, and we can surely say that on such and such a day they will be here or there." "But do you not fear—" "Murder?" The queen finished the phrase. "I know that might befall; but they may hold us as hostages for their necks when vengeance impends. However, nothing venture, nothing win."
  • 58. "And when do the allied sovereigns expect to be in Paris?" inquired Mme. Campan. "Between the fifteenth and twentieth of August," was the reply. "God grant it!" said the lady. But the prayer was not granted; or, if heard, Heaven sent France the succor she had not dreamed of—the Marseillaise Hymn of Liberty.
  • 59. CHAPTER VII. THE MEN FROM MARSEILLES. We have said that Barbaroux had written to a friend in the south to send him five hundred men willing to die. Who was the man who could write such lines? and what influence had he over his friends? Charles Barbaroux was a very handsome young man of barely twenty-five, who was reproached for his beauty, and considered by Mme. Roland as frivolous and too generally amorous. On the contrary, he loved his country alone, or must have loved her best, for he died for her. Son of a hardy sea-faring man, he was a poet and orator when quite young—at the breaking out of trouble in his native town during the election of Mirabeau. He was then appointed secretary to the Marseilles town board. Riots at Arles drew him into them; but the seething caldron of Paris claimed him; the immense furnace which needed perfume, the huge crucible hissing for purest metal. He was Roland's correspondent at the south, and Mme. Roland had pictured from his regular, precise, and wise letters, a man of forty, with his head bald from much thinking, and his forehead wrinkled with vigils. The reality of her dream was a young man, gay, merry, light, fond of her sex, the type of the rich and brilliant generation flourishing in '92, to be cut down in '93. It was in this head, esteemed too frivolous by Mme. Roland, that the first thought of the tenth of August was conceived, perhaps. The storm was in the air, but the clouds were tossing about in all directions for Barbaroux to give them a direction and pile them up
  • 60. over the Tuileries. When nobody had a settled plan, he wrote for five hundred determined men. The true ruler of France was the man who could write for such men and be sure of their coming. Rebecqui chose them himself out of the revolutionists who had fought in the last two years' popular affrays, in Avignon and the other fiery towns; they were used to blood; they did not know what fatigue was by name. On the appointed day they set out on the two hundred league tramp, as if it were a day's strolling. Why not? They were hardy seamen, rugged peasants, sunburned by the African simoom or the mountain gale, with hands callous from the spade or tough with tar. Wherever they passed along they were hailed as brigands. In a halt they received the words and music of Rouget de l'Isle's "Hymn to Liberty," sent as a viaticum by Barbaroux to shorten the road. The lips of the Marseilles men made it change in character, while the words were altered by their new emphasis. The song of brotherhood became one of death and extermination—forever "the Marseillaise." Barbaroux had planned to head with the Marseilles men some forty thousand volunteers Santerre was to have ready to meet them, overwhelm the City Hall and the House, and then storm the palace. But Santerre went to greet them with only two hundred men, not liking to let the strangers have the glory of such a rush. With ardent eyes, swart visages, and shrill voices, the little band strode through all Paris to the Champs Elysées, singing the thrilling song. They camped there, awaiting the banquet on the morrow. It took place, but some grenadiers were arrayed close to the spot, a Royalist guard set as a rampart between them and the palace.
  • 61. They divined they were enemies, and commencing by insults, they went on to exchanging fisticuffs. At the first blood the Marseillaise shouted "To arms!" raided the stacks of muskets, and sent the grenadiers flying with their own bayonets. Luckily, they had the Tuileries at their backs and got over the draw-bridge, finding shelter in the royal apartments. There is a legend that the queen bound up the wounds of one soldier. The Federals numbered five thousand—Marseilles men, Bretons, and Dauphinois. They were a power, not from their number, but their faith. The spirit of the revolution was in them. They had fire-arms but no ammunition; they called for cartridges, but none were supplied. Two of them went to the mayor and demanded powder, or they would kill themselves in the office. Two municipal officers were on duty—Sergent, Danton's man, and Panis, Robespierre's. Sergent had artistic imagination and a French heart; he felt that the young men spoke with the voice of the country. "Look out, Panis," he said; "if these youths kill themselves, the blood will fall on our heads." "But if we deliver the powder without authorization, we risk our necks." "Never mind. I believe the time has come to risk our necks. In that case, everybody for himself," replied Sergent. "Here goes for mine; you can do as you like." He signed the delivery note, and Panis put his name to it. Things were easier now; when the Marseilles men had powder and shot they would not let themselves be butchered without hitting back.
  • 62. As soon as they were armed, the Assembly received their petition, and allowed them to attend the session. The Assembly was in great fear, so much so as to debate whether it ought not to transfer the meetings to the country. For everybody stood in doubt, feeling the ground to quake underfoot and fearing to be swallowed. This wavering chafed the southerners. No little disheartened, Barbaroux talked of founding a republic in the south. He turned to Robespierre, to see if he would help to set the ball rolling. But the Incorruptible's conditions gave him suspicions, and he left him, saying: "We will no more have a dictator than a king."
  • 63. CHAPTER VIII. THE FRIEND IN NEED. The very thing encouraging the Tuileries party was what awed the rebels. The palace had become a formidable fortress, with a dreadful garrison. During the night of the fourth of August, the Swiss battalions had been drawn from out of town into the palace. A few companies were left at Gaillon, where the king might take refuge. Three reliable leaders were beside the queen: Maillardet with his Switzers, Hervilly with the St. Louis Knights and the Constitutional Guard, and Mandat, who, as National Guard commander, promised twenty thousand devoted and resolute fighting men. On the evening of the eighth a man penetrated the fort; everybody knew him, so that he had no difficulty in passing to the queen's rooms, where they announced "Doctor Gilbert." "Ah, welcome, welcome, doctor!" said the royal lady, in a feverish voice, "I am happy to see you." He looked sharply at her, for on the whole of her face was such gladness and satisfaction that it made him shudder. He would sooner have seen her pale and disheartened. "I fear I have arrived too late," he said. "It is just the other way, doctor," she replied, with a smile, an expression her lips had almost forgotten how to make; "you come at
  • 64. the right time, and you are welcome. You are going to see what I have long yearned to show you—a king really royal." "I am afraid, madame, that you are deceiving yourself," he returned, "and that you will exhibit rather the commandant of a fort." "Perhaps, Doctor Gilbert, we can never come to a closer understanding on the symbolical character of royalty than on other matters. For me a king is not solely a man who may say, 'I do not wish,' but one who can say, 'Thus I will.'" She alluded to the famous veto which led to this crisis. "Yes, madame," said Gilbert, "and for your majesty, a king is a ruler who takes revenge." "Who defends himself," she retorted; "for you know we are openly threatened, and are to be attacked by an armed force. We are assured that five hundred desperadoes from Marseilles, headed by one Barbaroux, took an oath on the ruins of the Bastile, not to go home until they had camped on the ruins of the Tuileries." "Indeed, I have heard something of the kind," remarked Gilbert. "Which only makes you laugh?" "It alarms me for the king and yourself, madame." "So that you come to propose that we should resign, and place ourselves at the mercy of Messieurs Barbaroux and his Marseilles bullies?" "I only wish the king could abdicate and guarantee, by the sacrifice of his crown, his life and yours, and the safety of your children." "Is this the advice you give us, doctor?" "It is; and I humbly beseech you to follow it."
  • 65. "Monsieur Gilbert, let me say that you are not consistent in your opinions." "My opinions are always the same, madame. Devoted to king and country, I wished him to be in accord with the Constitution; from this desire springs the different pieces of counsel which I have submitted." "What is the one you fit to this juncture?" "One that you have never had such a good chance to follow. I say, get away." "Flee?" "Ah, you well know that it is possible, and never could be carried out with greater facility. You have nearly three thousand men in the palace." "Nearer five thousand," said the queen, with a smile of satisfaction, "with double to rise at the first signal we give." "You have no need to give a signal, which may be intercepted; the five thousand will suffice." "What do you think we ought to do with them?" "Set yourself in their midst, with the king and your august children; dash out when least expected; at a couple of leagues out, take to horse and ride into Normandy, to Gaillon, where you are looked for." "You mean, place ourselves under the thumb of General Lafayette?" "At least, he has proved that he is devoted to you." "No, sir, no! With my five thousand in hand, and as many more ready to come at the call, I like another course better—to crush this revolt once for all." "Oh, madame, how right he was who said you were doomed."
  • 66. "Who was that, sir?" "A man whose name I dare not repeat to you; but he has spoken three times to you." "Silence!" said the queen, turning pale; "we will try to give the lie to this prophet of evil." "Madame, I am very much afraid that you are blinded." "You think that they will venture to attack us?" "The public spirit turns to this quarter." "And they reckon on walking in here as easily as they did in June?" "This is not a stronghold." "Nay; but if you will come with me, I will show you that we can hold out some time." With joy and pride she showed him all the defensive measures of the military engineers and the number of the garrison whom she believed faithful. "That is a comfort, madame," he said, "but it is not security." "You frown on everything, let me tell you, doctor." "Your majesty has taken me round where you like; will you let me take you to your own rooms, now?" "Willingly, doctor, for I am tired. Give me your arm." Gilbert bowed to have this high favor, most rarely granted by the sovereign, even to her intimate friends, especially since her misfortune. When they were in her sitting-room he dropped on one knee to her as she took a seat in an arm-chair.
  • 67. "Madame," said he, "let me adjure you, in the name of your august husband, your dear ones, your own safety, to make use of the forces about you, to flee and not to fight." "Sir," was the reply, "since the fourteenth of July, I have been aspiring for the king to have his revenge; I believe the time has come. We will save royalty, or bury ourselves under the ruins of the Tuileries." "Can nothing turn you from this fatal resolve?" "Nothing." She held out her hand to him, half to help him to rise, half to send him away. He kissed her hand respectfully, and rising, said: "Will your majesty permit me to write a few lines which I regard as so urgent that I do not wish to delay one instant?" "Do so, sir," she said, pointing to a writing-table, where he sat down and wrote these lines: "My Lord,—Come! the queen is in danger of death, if a friend does not persuade her to flee, and I believe you are the only one who can have that influence over her." "May I ask whom you are writing to, without being too curious?" demanded the lady. "To the Count of Charny, madame," was Gilbert's reply. "And why do you apply to him?" "For him to obtain from your majesty what I fail to do." "Count Charny is too happy to think of his unfortunate friends; he will not come," said the queen. The door opened, and an usher appeared.
  • 68. "The Right Honorable, the Count of Charny," he announced, "desiring to learn if he may present his respects to your majesty." The queen had been pale, and now became corpse-like, as she stammered some unintelligible words. "Let him enter," said Gilbert; "Heaven hath sent him." Charny appeared at the door in naval officer's uniform. "Oh, come in, sir; I was writing for you," said the physician, handing him the note. "Hearing of the danger her majesty was incurring, I came," said the nobleman, bowing. "Madame, for Heaven's sake, hear and heed what Count Charny says," said Gilbert; "his voice will be that of France." Respectfully saluting the lord and the royal lady, Gilbert went out, still cherishing a last hope.
  • 69. CHAPTER IX. CHARNY ON GUARD. On the night of the ninth of August, the royal family supped as usual; nothing could disturb the king in his meals. But while Princess Elizabeth and Lady Lamballe wept and prayed, the queen prayed without weeping. The king withdrew to go to confession. At this time the doors opened, and Count Charny walked in, pale, but perfectly calm. "May I have speech with the king?" he asked, as he bowed. "At present I am the king," answered Marie Antoinette. Charny knew this as well as anybody, but he persisted. "You may go up to the king's rooms, count, but I protest that you will very much disturb him." "I understand; he is with Mayor Petion." "The king is with his ghostly counselor," replied the lady, with an indescribable expression. "Then I must make my report to your majesty as major-general of the castle," said the count. "Yes, if you will kindly do so." "I have the honor to set forth the effective strength of our forces. The heavy horse-guards, under Rulhieres and Verdiere, to the number of six hundred, are in battle array on the Louvre grand square; the Paris City foot-guards are barracked in the stables; a hundred and fifty are drawn from them to guard at Toulouse House,
  • 70. at need, the Treasury and the discount and extra cash offices; the Paris Mounted Patrol, only thirty men, are posted in the princes' yard, at the foot of the king's back stairs; two hundred officers and men of the old Life Guards, a hundred young Royalists, as many noblemen, making some four hundred combatants, are in the Bull's- eye Hall and adjoining rooms; two or three hundred National Guards are scattered in the gardens and court-yards; and lastly, fifteen hundred Swiss, the backbone of resistance, are taking position under the grand vestibule and the staircases which they are charged to defend." "Do not all these measures set you at ease, my lord?" inquired the queen. "Nothing can set me at ease when your majesty's safety is at stake," returned the count. "Then your advice is still for flight?" "My advice, madame, is that you ought, with the king and the royal children, be in the midst of us." The queen shook her head. "Your majesty dislikes Lafayette? Be it so. But you have confidence in the Duke of Liancourt, who is in Rouen, in the house of an English gentleman of the name of Canning. The commander of the troops in that province has made them swear allegiance to the king; the Salis- Chamade Swiss regiment is echeloned across the road, and it may be relied on. All is still quiet. Let us get out over the swing-bridge, and reach the Etoille bars, where three hundred of the horse-guards await us. At Versailles, we can readily get together fifteen hundred noblemen. With four thousand, I answer for taking you wherever you like to go." "I thank you, Lord Charny. I appreciate the devotion which made you leave those dear to you, to offer your services to a foreigner."
  • 71. "The queen is unjust toward me," replied Charny. "My sovereign's existence is always the most precious of all in my eyes, as duty is always the dearest of virtues." "Duty—yes, my lord," murmured the queen; "but I believe I understand my own when everybody is bent on doing theirs. It is to maintain royalty grand and noble, and to have it fall worthily, like the ancient gladiators, who studied how to die with grace." "Is this your majesty's last word?" "It is—above all, my last desire." Charny bowed, and as he met Mme. Campan by the door, he said to her: "Suggest to the princesses that they should put all their valuables in their pockets, as they may have to quit the palace without further warning." While the governess went to speak to the ladies, he returned to the queen, and said: "Madame, it is impossible that you should not have some hope beyond the reliance on material forces. Confide in me, for you will please bear in mind that at such a strait, I will have to give an account to the Maker and to man for what will have happened." "Well, my lord," said the queen, "an agent is to pay Petion two hundred thousand francs, and Danton fifty thousand, for which sums the latter is to stay at home and the other is to come to the palace." "Are you sure of the go-betweens?" "You said that Petion had come, which is something toward it." "Hardly enough; as I understood that he had to be sent for three times."
  • 72. "The token is, in speaking to the king, he is to touch his right eyebrow with his forefinger—" "But if not arranged?" "He will be our prisoner, and I have given the most positive orders that he is not to be let quit the palace." The ringing of a bell was heard. "What is that?" inquired the queen. "The general alarm," rejoined Charny. The princesses rose in alarm. "What is the matter?" exclaimed the queen. "The tocsin is always the trumpet of rebellion." "Madame," said Charny, more affected by the sinister sound than the queen, "I had better go and learn whether the alarm means anything grave." "But we shall see you again?" asked she, quickly. "I came to take your majesty's orders, and I shall not leave you until you are out of danger." Bowing, he went out. The queen stood pensive for a space, murmuring: "I suppose we had better see if the king has got through confessing." While she was going out, Princess Elizabeth took some garments off a sofa in order to lie down with more comfort; from her fichu she removed a cornelian brooch, which she showed to Mme. Campan; the engraved stone had a bunch of lilies and the motto: "Forget offenses, forgive injuries." "I fear that this will have little influence over our enemies," she remarked; "but it ought not be the less dear to us."
  • 73. As she was finishing the words, a gunshot was heard in the yard. The ladies screamed. "There goes the first shot," said Lady Elizabeth. "Alas! it will not be the last." Mayor Petion had come into the palace under the following circumstances. He arrived about half past ten. He was not made to wait, as had happened before, but was told that the king was ready to see him; but to arrive, he had to walk through a double row of Swiss guards, National Guards, and those volunteer royalists called Knights of the Dagger. Still, as they knew he had been sent for, they merely cast the epithets of "traitor" and "Judas" in his face as he went up the stairs. Petion smiled as he went in at the door of the room, for here the king had given him the lie on the twentieth of June; he was going to have ample revenge. The king was impatiently awaiting. "Ah! so you have come, Mayor Petion?" he said. "What is the good word from Paris?" Petion furnished the account of the state of matters—or, at least, an account. "Have you nothing more to tell me?" demanded the ruler. "No," replied Petion, wondering why the other stared at him. Louis watched for the signal that the mayor had accepted the bribe. It was clear that the king had been cheated; some swindler had pocketed the money. The queen came in as the question was put to Petion. "How does our friend stand?" she whispered. "He has not made any sign," rejoined the king.
  • 74. "Then he is our prisoner," said she. "Can I retire?" inquired the mayor. "For God's sake, do not let him go!" interposed the queen. "Not yet, sir; I have something yet to say to you," responded the king, raising his voice. "Pray step into this closet." This implied to those in the inner room that Petion was intrusted to them, and was not to be allowed to go. Those in the room understood perfectly, and surrounded Petion, who felt that he was a prisoner. He was the thirtieth in a room where there was not elbow-room for four. "Why, gentlemen, we are smothering here," he said; "I propose a change of air." It was a sentiment all agreed with, and they followed him out of the first door he opened, and down into the walled-in garden, where he was as much confined as in the closet. To kill time, he picked up a pebble or two and tossed them over the walls. While he was playing thus, and chatting with Roederer, attorney of the province, the message came twice that the king wanted to see him. "No," replied Petion; "it is too hot quarters up there. I remember the closet, and I have no eagerness to be in it again. Besides, I have an appointment with somebody on the Feuillants' Quay." He went on playing at clearing the wall with stones. "With whom have you an appointment?" asked Roederer. At this instant the Assembly door on the Feuillants' Quay opened. "I fancy this is just what I was waiting for," remarked the mayor.
  • 75. "Order to let Mayor Petion pass forth," said a voice; "the Assembly demands his presence at the bar of the House, to give an account of the state of the city." "Just the thing," muttered Petion. "Here I am," he replied, in a loud voice; "I am ready to respond to the quips of my enemies." The National Guards, imagining that Petion was to be berated, let him out. It was nearly three in the morning; the day was breaking. A singular thing, the aurora was the hue of blood.
  • 76. CHAPTER X. BILLET AND PITOU. On being called by the king, Petion had foreseen that he might more easily get into the palace than out, so he went up to a hard-faced man marred by a scar on the brow. "Farmer Billet," said he, "what was your report about the House?" "That it would hold an all-night sitting." "Very good; and what did you say you saw on the New Bridge?" "Cannon and Guards, placed by order of Colonel Mandat." "And you also stated that a considerable force was collected under St. John's Arcade, near the opening of St. Antoine Street?" "Yes; again, by order of Colonel Mandat." "Well, will you listen to me? Here you have an order to Manuel and Danton to send back to barracks the troops at St. John's Arcade, and to remove the guns from the bridge; at any cost, you will understand, these orders must be obeyed." "I will hand it to Danton myself." "Good. You are living in St. Honore Street?" "Yes, mayor." "When you have given Danton the order, get home and snatch a bit of rest. About two o'clock, go out to the Feuillants' Quay, where you will stand by the wall. If you see or hear stones falling over from the other side of the wall, it will mean that I am a prisoner in the Tuileries, and detained by violence."
  • 77. "I understand." "Present yourself at the bar of the House, and ask my colleagues to claim me. You understand, Farmer Billet, I am placing my life in your hands." "I will answer for it," replied the bluff farmer; "take it easy." Petion had therefore gone into the lion's den, relying on Billet's patriotism. The latter had spoken the more firmly, as Pitou had come to town. He dispatched the young peasant to Danton, with the word for him not to return without him. Lazy as the orator was, Pitou had a prevailing way, and he brought Danton with him. Danton had seen the cannon on the bridge, and the National Guards at the end of the popular quarter, and he understood the urgency of not leaving such forces on the rear of the people's army. With Petion's order in hand, he and Manuel sent the Guards away and removed the guns. This cleared the road for the Revolution. In the meantime, Billet and Pitou had gone to their old lodging in St. Honore Street, to which Pitou bobbed his head as to an old friend. The farmer sat down, and signified the young man was to do the same. "Thank you, but I am not tired," returned Pitou; but the other insisted, and he gave way. "Pitou, I sent for you to join me," said the farmer. "And you see I have not kept you waiting," retorted the National Guards captain, with his own frank smile, showing all his thirty-two teeth. "No. You must have guessed that something serious is afoot."
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