The Sun in Eclipse PDF
Preview The Sun in Eclipse
Practical Astronomy Springer-V erlag Berlin Heidelherg GmhH Other titles in this series TheObservationalAmateurAstronomer PatrickMoore (Ed.) TheModernAmateurAstronomer PatrickMoore (Ed.) TelescopesandTechniques CR. Kitchin SmallAstronomicalObservatories PatrickMoore (Ed.) TheArtandScienceofCCDAstronomy DavidRatledge (Ed.) TheObserver'sYear PatrickMoore SeeingStars ChrisKitchin andRobertW. Forrest Photo-guideto theConstellations ChrisKitchin Michael Maunder and Patrick Moore , Springer Cover illustrations: Front cover: A montage capturing the "miracle" of the Sun in eclipse - a Pinatubo volcanic ash sunset seen in Namibia, together with a solar eclipse seen in Kenya in 1980 (Michael Maunder). Back cover (background): A solar eclipse seen in Rajasthan in 1995 (Peter Cattermole). Back cover (inset): The "Diamond Ring" effect seen at the 1976 eclipse in Zanzibar (Michael Maunder). ISBN 978-3-540-76146-4 British Library Cataloguing in Publication Data Maunder, Michael The sun in eclipse. - (Practical astronomy) 1. Solar eclipses 1. Title II. Moore, Patrick, 1923- 523.7'8 ISBN 978-3-540-76146-4 ISBN 978-1-4471-0529-9 (eBook) DOI 10.1007/978-1-4471-0529-9 Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be repro duced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of repro graphic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concern ing reproduc tion outside those terms should be sent to the publishers. © Springer-Verlag Berlin Heide1berg 1998 Originally pub1ished by Springer-Verlag Berlin Heide1berg New York in 1998 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and there fore free for general use. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. Typeset by EXPO Holdings, Malaysia 58/3830-5432 Printed on acid-free paper Fore~ord Total eclipses ofthe Sun are always fascinating. They no longer cause alarm in civilised countries, but they do excite a tremendous amount ofinterest. They are also scientifically important, since they allow Earth based observers to view phenomena which can never beproperlyseenatothertimes. AsseenfromanyonelocationontheEarth'ssurface, totalsolareclipsesarerare;thusEnglandsawnototality between 1927and 1999,and then mustwait until2090. Therefore,would-beeclipseviewersmusttraveltoother partsoftheworld.Thismeanscarefulpreparation. In this book,wehavedone ourbestto explainwhat eclipsesare;whatphenomenacanbeseen;whatplans mustbemade; and- mostimportantly- whatare the procedures for scientific work and photography. Full instructions are given based on the authors' personal experience,andwehopethatwhatwehavewrittenwill beofusetoothers. Thisisanappropriatetimeto produceabookofthis nature, because on 11 August 1999 a total eclipse will be seen from parts ofCornwall and Devon, as well as Alderney in the Channel Islands. So let us hope for clearskies - andifweare unlucky,preparetojourney to other countries for the eclipses due in the next few years. MichaelMaunder PatrickMoore Contents Sun,MoonandStars . 2 DaytimeStar 13 3 ObservingtheSun ........................ 27 4 Eclipses- GeneralPrinciples 49 5 EclipsesinHistory 59 6 TheDevelopmentofEclipsePhotography 65 7 PartialEclipses 77 8 AnnularEclipses- andEclipse Photography. ............................ 93 9 EclipseChasing 109 10 TotalEclipses....... .. 137 11 The1999Eclipse 159 12 EclipseMishapsandOddities.............. 165 13 EclipsesoftheFuture .............. 171 14 EclipsesElsewhere. ....................... 183 AppendixA- CassetteLoads 185 AppendixB- CloudTypes 189 AppendixC- SuggestedTotalSolarEclipse Exposures 193 AppendixD- FieldofViewofCameraLenses .. 197 AppendixE- Sun/MoonTransitTimes 201 AppendixF- CheckListsofItemstotake onEclipses 205 Index 209 ..A· \Ii Total eclipse Theumbrol shadowoftheMoon reaches all thewayto theEorth. Outsidethe umbra, approximately one thirdofthe Earth'sdoylitsurfacewill seeapartial eclipse. How itlooks 0···••::::.. ::.......:.:;:. .........- ··~O" Earth Sun o Annulareclipse In thistypeofeclipse, the umbrol shadow fallsshortofthe Earth'ssurface, becausetheMoon istoo forawaytoobscuretheSunentirely. . .. ··············..:···:::::::':::.:::::::::::':::' :::.. .:. .' 0 .::::~ .........., :.:.:::::::::..,.::'-::: .:..Mo~~'" ". .._-.--.--- _ -.- - . '0 Sun Earth Partial eclipse In thistypeofeclipse, theMoon'sumbra missesthe Earthentirely. Viewed from theEarth, all thatis visibleistheSun partiallycovered bytheMoon. Howitlooks Jntroduction_______ On 11 August 1999 there will be a total eclipse ofthe Sun. The track of totality will cross England, and clouds permitting! - people in parts ofCornwall and Devon will be able to watch the first English total eclipse since 1927. They will see the dark disk ofthe Moon encroach upon the brilliance ofthe Sun, finally blotting it out and revealing the glory of the solar atmosphere,withthepearlycoronaandtheredpromi nences which look so uncannily like flames. The sky will darken, and for a few fleeting moments it will almostseemasthoughNaturehascometo ahalt. Of course eclipses have been observed since very ancient times, and to our ancestors they were very alarmingphenomena. Even todaythere are still some peoplewhoarebyno meanssurehoweclipsehappens. Abasicunderstandingofthe make-up ofthe universe mustbethefirst stepintheexplanation,soletusbegin with a briefdescription ofthe main characters in the cosmicstory. TheEarthuponwhichweliveisaplanet,7926miles (12,756 km) in diameter, moving round the Sun at a distanceof93,000,000miles (150,000,000km). TheSun itselfisanordinarystar,andallthestarswecanseeon anyclear night are themselves suns, manyofthem far larger, hotterand moreluminousthan ours. Theyare, of course, much further away, and their remoteness meansthatordinaryunitsofmeasurementsuchasthe mileandthekilometrebecomehopelesslyinconvenient The Sun in Eclipse - justas itwouldbe cumbersome to give the distance betweenLondonandManchesterininches. Instead,we use the light-year. Light does not travel instanta neously;itflashes alongat 186,000miles (300,000km) per second, so that in a year it can cover almost 6millionmillionmiles (9.4millionmillionkm). Thisis the astronomical light-year, which please note, is a measureofdistance, notoftime. Eventheneareststar beyondtheSunisover4light-yearsaway.Ontheother hand it takes light only 8.6 minutes to reach us from the Sun, and it can pass between the Earth and the Mooninlessthantwoseconds. TheSunisthecentreoftheSolarSystem- ourhomein space.Therearenineplanets,ofwhichtheEarthcomes third in order ofdistance. The planetshave no light of theirown, andshineonlybecausetheyarebeinglit up bytheSun,sothatifsomemalevolentdemonsuddenly snatchedtheSunoutoftheskytheplanetswouldvanish too- thoughthestarswouldbecompletelyunaffected. Anyrough plan ofthe SolarSystem showsthat itis dividedintotwowell-markedparts.Firsttherearefour relatively small, rocky planets: Mercury, Venus, the Earth and Mars. Next comes a region in which move many thousands of dwarf worlds known as minor planets or asteroids, and then follow four giants: Jupiter, Saturn, Uranus and Neptune, together with a peculiarlittlebody,Pluto,whichmaynotbeworthyof true planetary status. The main details about the planetsarebestsummarisedinTable 1.1. Most planetary orbits are not very different from circles,butPlutoisanexception;itsdistancefrom the Sun ranges between 2766 million and 4583 million miles (4425 and 7375 million km), so that it spends part ofits time closer-in than Neptune; between 1979 and 1999Neptune,notPluto,istheoutermostmember of the planetary family. Pluto is also exceptional in another way. In general the planets move roughly in the sameplane, sothat ifyou draw aplanofthe Solar System on aflat table you are notveryfar wrong, but Pluto'sorbitalinclinationis 17degrees,sothatthereis nofearofacollisionwithNeptune. The first five planets have been known since early times,becausetheyarenaked-eyeobjects.OnlyMercury Sun, Moon and Stars Table 1.1.Theplanetsofour SolarSystem Plonet MeonDistance Orbital Axial Equatorial Diameter MassPlone> from the Sun Period Rotation miles km Mass~a,'" millionsof (equatorial) miles km Mercury 36.0 57.9 88 days 58.2 days 3030 4878 0.055 Venus 67.2 108.2 224.7days 243.2days 7523 12,104 0.816 Earth 93.0 148.6 365.3 days 23h 56m 4s 7926 12,756 1 Mars 141.5 227.9 587.0days 24h 37m 22s 4222 6794 0.107 Jupiter 483 778 11.9yeors 9h50m 30s 89,424 143,884 1319 Saturn 886 1427 29.5years 10h 13m59s 74,914 120,536 744 Uranus 1783 2870 84.0years 17h 14m 31,770 51,118 14.6 Neptune 2793 4497 164.8years 16h6m 31,410 50,538 17.2 Pluto 3666 5900 247.7years 6d9h 17s 1444 2324 0.002 is not obtrusive, because it always keeps in the same partoftheskyastheSunandcanneverbeseenagainst a really dark background; Venus and Jupiter far out shine any star, and so does Mars at its best, while Saturn is bright enough to be very conspicuous. The three outermostplanets have been discoveredonlyin modern or near-modern times: Uranus in 1781, Neptunein 1846andPlutoas recentlyas 1930.Uranus canjustbeseenwith thenakedeyeifyouknowwhere to look for it, and binoculars will show Neptune, but Plutoisverymuchfainter. Thestarsaresofar awaythattheirindividualmove mentsareveryslight;the constellationpatternswhich weseetodayareto allintentsandpurposesthesameas those which must have been seen by Julius Cresar, Homer or even the builders of the Pyramids. The planets, however, wander around from one constella tiontoanother;becausetheyaremovingroughlyinthe same plane (again with the exception of Pluto) they keep to a well-defined band round the sky known as theZodiac. Each planet has its own special characteristics. Mercury is rocky and barren, with almost no atmos phere; Venus has a very dense atmosphere, made up chieflyofthegascarbondioxide- andsincetheclouds containlargequantitiesofsulphuricacid, anyform of life there is most improbable! Telescopically, both MercuryandVenusshowphases,orapparentchanges ofshape from newto full. Obviouslythe Sun can illu minate onlyhalfofa planet at anyone time, and our view depends upon how much of the sunlit side is turned in our direction. Very occasionally these two
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