Astronomy for Everyman PDF
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ASTROINOMY ASTRONOMY FOR EVERYMAN FOR EVERYMAN Edited by Dr M. DAVIDSON SOLAR SYSTEM THE SUN THE MOON THE PLANETS MINOR PLANETS PMETS, METEORS AURORA AND ZODIACAL LIGHT THE STARS LIGHT AND INSTRUMENTS HISTORY OF ASTRONOMY NAVIGATION THE ROAD TO THE PLANETS NOTES ON IDENTIFICATION Edited by MARTIN DAVIDSON B.A., D.Sc., F.RA.S. DENT With contributions by leading Astronomers, including Directors ofSections ofthe British Astronomical Association MM ;"C^ ' .' -': '' :-..-. . i<ro SOUTHERN SKY NORTHERN SKY XX XX Vlll StarMagnitudes VIII The northern and southern skies extended respectively to 40° south and 40 north of the equator. Stars up to magnitude 4 are shown. The Romannumeralsroundtheedgereferto Right Ascension, and the numbered circles to Declination, each circle being separated by 30°. ASTRONOMY FOR EVERYMAN Edited by MARTIN DAVIDSON B.A., D.Sc, F.R.A.S. Contributors M. B. B. HEATH, F.R.A.S. F. J. SELLERS, M.I.MECH.E., F.R.A.S. DR. H. P. WILKINS, F.R.A.S. F. O'D. ALEXANDER, M.A., PH.D., F.R.A. MARTIN DAVIDSON, B.A., D.SC, F.R.A.S. W. B. HOUSMAN, F.R.A.S. P. DOIG, F.R.A.S. E. G. MARTIN, F.R.A.S. H. L. KELLY, F.R.I.B.A., F.R.A.S. J. B. PARKER, M.A. W. A. SCOTT, B.SC, F.R.A.S. A. C. CLARKE, B.SC, F.R.A.S. E. O. TANCOCK, B.A., F.R.A.S. R. Obs., Greenwich DELAVAN'S COMET, 1914 26th September, Greenwich LONDON: M. DENT & SONS LTD J. NEW YORK: E. P. DUTTON & CO. INC. ' All rights reserved by M. DENT & SONS LTD J. Aldine House • Bedford Street • London Made in Great Britain CONTENTS at The Aldine Press Letchworth Herts Firstpublished 1953 page CHAP. Revisededition 1954 Preface ix Introduction: A General View of the Universe. By M. Davidson, B.A., D.Sc, F.R.A.S., President ofthe British Astronomical Association, 1936-8 xv The Solar System. By M. B. B. Heath, F.R.A.S., I Director of Saturn Section, British Astronomical Association II The Sun. By F. J. Sellers, M.I.Mech.E., F.R.A.S., DirectorofSolarSection,BritishAstronomicalAssocia- tion, 1937-51 III The Moon. By Dr. H. P. Wilkins, F.R.A.S., Director ofLunarSection, BritishAstronomicalAssociation 73 IV The Planets. By M. B. B. Heath, F.R.A.S., Director of Saturn Section, British Astronomical Association, and A. F. O'D. Alexander, M.A., Ph.D., F.R.A.S., Director of Jupiter Section, British Astronomical no Association V Minor Planets. By A. F. O'D. Alexander, M.A., Ph.D., F.R.A.S. 210 VI Comets, Meteors and Meteorites. By M. David- son, B.A., D.Sc, F.R.A.S.,formerlyDirectorofComet Section, British Astronomical Association 220 VII The Aurora and Zodiacal Light. By W. B. Hous- man, F.R.A.S.,formerlyDirectorofAurora andZodiacal Light Section, British Astronomical Association 262 VIII The Stars. By P. Doig, F.R.A.S., Editor of 'The Journal of the British Astronomical Association,' Author of'An Outline ofStellar Astronomy 286 vii CONTENTS Vlll CHAP. page IX Lightand Instruments. ByE. G. Martin, F.R.A.S., Senior Experimental Officer, Royal Observatory, Greenwich 358 PREFACE X History of Astronomy. By H. L. Kelly,F.R.I.B.A., F.R.A.S., Director of Historical Section, British Astronomical Association, and P. Doig, F.R.A.S. THIS book provides an up-to-date andauth—oritative outline Authorof 'A ConciseHistoryofAstronomy' 406 of our knowledge of the heavenly bodies their dist—ances, dimensions, masses, constitutions, temperatures, etc. and XI Navigation. ByJ. B. Parker, M.A., and W. A. Scott, explains themethods used by the astronomerforacquiring B.Sc,F.R.A.S,,H.M.NauticalAlmanacOffice 447 this knowledge. As far as possible anything except elementary XII The Road to the Planets. By Arthur C. Clarke, mathematical treatment of the problems has been avoided in the B.Sc,F.R.A.S.,ChairmanoftheBritishInterplanetary text, withthe exception ofthe chapteron Navigation. Whereithas Society. Author of 'Interplanetary Flight,' 'The Ex- seemed desirable more difficult mathematical matters have been plorationofSpace,'etc. 480 relegated to footnotes at the ends of chapters or to the Appendices which, however, are not essential for understanding the subjects XIII Notes on Identification. By E. 0. Tancock, B.A., outlined in the text. The various branches of astronomy are dealt F.R.A.S., Author of 'Starting Astronomy,' Editor of withbyspecialists, manyofthempresentorpastdirectorsofsections Philips' 'Chart ofthe Stars,' etc. 486 ofthe British Astronomical Association. As they have all made an ApFp.eRn.dAi.cSe.s I—X. By M. Davidson, B.A., D.Sc, 500 ienxtpeenrsiievnecestofudayssiosftitnhgeitrheomwenmpbaerrtiscuoflatrhesiurbsjeeccttisonasnwdhhoavweorhkaudndteher their direction, and also others who consult them for advice and Appendix XI. The Planets. By A. F. O'D. Alex- guidance, they understand the difficulties of beginners and know ander,M.A.,Ph.D.,F.R.A.S. 506 how to express themselves in language suitable to the novice as Appendix XII. Notes on the Nucleus of a Comet. well as to those who are more advanced. ByM.Davidson,B.A.,D.Sc, F.R.A.S. 508 owTnheplIanntertodtuocttihoenrgeimveosteagexetnrear-aglalsaucrtviecynoefbtuhleaeu,niavnerdsei,t fisrohmopoeudr Appendix XIII. Main Sequence Stars. By E. G. that this chapter will enable readers to gain a balanced perspective Martin,F.R.A.S. 508 of the subject before they embark on the specialized portions which are dealt with in the various chapters. After this general view of Appendix XIV. Note on the Spiral Structure of theGalaxy. ByM.Davidson,B.A.,D.Sc,F.R.A.S. 509 tthhee wsholoalresuynsitveemr,sestughgeesfitrisntgchaapstiemrploeutmliondeeslthoef mthaeinSufneataunrdesiotfs Index 511 family of planets, which can be easily visualized. This model will assist in giving an idea of the immense distances with which the Star Maps end-papers astronomer deals, even in the solar system which, compared with the distances ofstars andnebulae, is a mere speck in the universe. Chapter II deals with the Sun in relation toevolution and the life of man, its physical features, composition, the process by which its enormous output of heat and light is supplied and maintained, *A ix — X PREFACE PREFACE XI its relation to various terrestrial phenomena such as the aurora, astronomy and meteorology. Although its origin comes under the interference with short-wave radio transmission, etc., and also the province of astronomy the final cause of the phenomenon is largely methods used for observingsunspots, flares, prominences, and other of a meteorological character, but it is usually included in astro- features. The author of this chapter is well known for his work nomical works. It is not a common phenomenon in the southern on solar prominences and for the device that he invented several parts of this country, but is frequently seen in the northern parts years ago for facilitating the observations of prominences by the of Scotland. Statistics show that on the average it is observed a spectrohelioscope. He has copious illustrations—photographs and hundred times a year in Lerwick, twenty-five times in Edinburgh, line diagrams—in his chapter. and seven times in London. Most of the chapter is devoted to ChapterIIIgivesadetaileddescriptionofthenight-to-nightlunar descriptions of its appearance and will prove very helpful to those features that can be seen with a small telescope and will prove most who have the opportunity of observing this beautiful spectacle, but instructive andstimulatingtoeveryonewhohas anyinterestin our there is also a short account of the causes of the phenomenon. It nearestneighbour—the Moon. The author ofthis chapter, withhis must not be assumed that this explanation settles all the difficulties band of workers on lunar topography, has made a very'compre- connected with the aurora; many unsolved problems still remain hensive investigation of the surface of the Moon, and as a result he and probably will remain for a considerable time before the geo- has produced the largest map of the Moon in existence. This is in physicist has provided acomplete solution. twenty-five sections and when assembled is twenty-five feet in Except for the Introductio—n, the book has so far been concerned diameter; he is now engaged in producing a still larger map This with very parochial matters merely a survey of the solar system chapter, unlike many of the others, is practically self-contained and of which the outermost planet is only about 4,000 million miles can be read without reference to other parts of the book. Some from us. This distance shrinks into utter insignificance when who read it will probably want to purchase a small telescope, or if comparedwith the distance oftheneareststar, thelightfromwhich they cannot afford this, may feel disposed to make one for them- takesoverfouryearstoreachus. ChapterVIII, 'TheStars,' explains selves—not a difficult or expensive matter. Thus equipped they how the depths of space are plumbed and stellar distances deter- willfind a wonderfulrecreation in studying some of the largerlunar mined, how the stars are weighed, the nature of the instruments formations, with the assistance of the descriptions given in used by the astronomer to tell what stars are made of and what Chapter III. their temperatures are, how they came into existence, what their In Chapter IV each of the planets is dealt with separately, and end will be, and so on. Perhaps some who read this chapter will nothing of real interest or importance to readers has been over- wonder why astronomers waste their time in studying such trivial looked; the results of the most recent research on the planetary things as planets andtheir satel—lites, comets andmeteors, andother features, their atmospheres, physical conditions, dimensions etc members of the solar system all mere specks in the immense have been included and copious illustrations by photographs and universe. They will learn, however, that the solar system must be drawmgs—some of the latter by the authors themselves—are used as the base for operations, and unless the distance of the earth included. from the sun is first known, it would be impossible to proceed with Chapter V contains a short account of the minor planets or the computations of the —distances of the stars and nebulae planetoids (usually known as asteroids, though the term is mis- galactic and extra-galactic or of their masses, dimensions, move- leading), andChapterVIdealswithcomets,meteors, andmeteorites ments, temperatures, and many of their other characteristics. The These, with the planets and their thirty-one satellites, complete the methods adopted by the astronomer for deriving these are fully members of the solar system. explainedin the simplestmanner, andthereaderwillbeenlightened 'TheAuroraandZodiacalLight.'ChapterVII.hasnotbeenincluded on the step-by-step proce—dure from the use of t—he earth's diameter under the solar system; the aurora is a 'border-line case' between tofindtheSun'sdistance theastronomicalunit andthen fromthis Xll PREFACE PREFACE Xlll esaattvowaeahrfryusiy.nnaddrnretdIaehtddeeeixrdsltiirwasgaith-tttaghh-naryclietealahsclretisionwfcgoatnsnwhetdebaoeuryrsylts—aaaeraansnnhdddcuonomfmdnaprrejaoeermdtsashttatyiohtvifosecfmlaityntlonhlceiolpotorhnssoeefacaoivtelfeoendltusio,gsthio—tam-sapoybrtweeoheasulerslsrt oshsueftfluCftpdihfhcyuaeilpeo,btnfoteaonrnkamXdv;aIitIgishta,oetpmmirTeoaohntv.weiihcdRaoeolsaaardbeautciosnkettfgheurerloePusiltnnaetdndreotiwdsin,ul'clt,thfieoohrnsowuwhtbeoijvceeachrt,tmhaoenrfidecnhdwaahdiivrotmahanvnaceveroedyf apsrowbiltehmsthwehipcohwear foefwthheunhdurmeadnyemairnsdatgoogsreapepmleedwiintchapaabbslterusoef tphreopBorsietdismhaIknitnegr'pjloaunrenteayrsytSoocoitehteyrihseraevsepnolnsyibbloed,ieesx—pltahiensMhooownfiitrsits solution. useVderbyylitthtlee ausptrtoonothmiesr;poithnitshhaassbebeenensariedleagbaotuetd tthoeCihnaspttreurmeIntXs abmunatddeaitfwtiiestrfhwaiainrrdlysthtceehrentepaxliatnnettthwsae.tnttySheoomraetttmheiamryptytthytieoanrkrset,ahciahsnidtshaethfMeanotsoacsnhteiwmcielildefbaoe,r pmwoihrintcdihsonohsfabsreecbaaedueesnrespiwutirstpihonstmerlaoynduyrcetsdieeotrnavieeldasrfltoiherarttwhwoeouuellndddhhoaafvvetehbecuardudesesecndreidmptotirhveee minafCkohiranmpgattetirhoenXjIfooIurIr,indee'ynNtiositfneyositnogsnothfIeadnestntatasirtfsiiccianatstihoienti,sr'esesemuasps.polnise.s the necessary mcoannfyusion than enlightenment. Throughout the book there are The book ends with a number of Appendices to explain more instrumcernotsss-reemfpelreonyceeds,, asnodmeitofwiltlhbeemfdoiurnedctiandgviastatbelnetitoonretfoerthteo afunldlybcaecrktaeinndp-opianptesrsinatshweeltlexat.s inStCahrapMtaeprsXaIrIeI.printed on thefront tthheasnesjtuusdtyaisngthtehioscccahsaipotnerarfiisresst.ofOanllt(htehowuhgohlethtihsiscawinllbebedboenteteirf SteIasvheonuslodn,liDker.toA.acFk.noOw'lDe.dgAeletxhaendaesrsi,staanndceMrre.ndPe.rDeodibg,y1Dwrh.oW.reHa.d parriesfeesrrweidl)l,tahnedntbheepmroarceticoablviaopupsl.ication to anyspecificproblem that through the manuscript and galley proofs and made a nu—mber of oCfhaNtpohteewrdoerXvk,eloownphamisectnhrtosisniodnmiyvtihiedsecsdoumbijpneltceott,etawwonidtshetochutitisoshnosa,mseobnheieesntdoperaricloaivlnigsdkewedittcihnh vsmmeaauvltseuttrae,abrllstehceawsrseueergfsgeoreteshg,tiiisvoaehncnsac.sebpoytcWcrtheuhesreprroeeandsu—ditibhfitoflhreiesrteyfnoicfnfeaolsrthdoteefhceivosapviriioinenoiwsuossnonecaxhrcpaoorpsnetetsersroesvda,e.nrwdsihaionl thotstAdathfhhiuhhssiesreotntsocaorwdrrospuosiroivtengeneenerrohvsgrdoiomeimonibanehyedciostbeorgamaeoowaolryeufRstn,nto,dtrdrtyhyeahtieaevdpnhnlaieeece,ondvlesardeonhprupmlitplerpotsuoymaoeurupegvtpaysrmneoe,oseentrftsrsnlsserttttfy.rrcohisrieenetbodnaoifoemtcomosdrtnetitotirhheimhodseamsenurevtarfsaeehri.ogaenynrritdlgmvdaituiTakehetnlhyesonhgatinsdwetse,teaopnfiifdlicsmdarbiFesutacretlshriesfaeeitftaminwoasmnsgcoonottieudstenhtvchteaeleeedtoinrgimpntylrnepiuatogodrbshtsoitdreseifelatstsffeoniqoitrcrouuohoyshnefretf goAptnofirsubuoasAbtFmnrpelricsberhinokepvssanntar;rhloootolemoodwydtiirfulhtcicsIeeipaetnldslipanwgouti1aAmnfebss9mosselsh2rienoa3chstcntapaiotdebsaaiirystrdomtiebniihoaesHasalnieugssnnnhtrioaskacoaennhvmmmrdtiesatahnetddemtsdoaeoeeolUnsombron.tfnebeiorepkrtotrrieaehTmosnpedhddrsnueSloewScu.pydhtelmuCaoecgboteniAdeeudhdvsinr.oeacavunvigNeorelrarfpayveommopfryfsaulmbdatiTlDrheasieghesnsepeicdhHaooeennnrrBaputstrvhrmfimeooitbaentrbiennsousdr,t--ha pcswfirheiroactTstvpohhetneosedifrntpwdormCeoahhaacaodltyipiimftncfngeaiholcruatmlsaXtobpIrhiep;telaicedtcaaehasnsittipshlibeeyoechniapuoasrnlmoadlficbyetteratieswescntiadtlotrcwohoeoidnxmttopphbhemioyeryluieteetdtnvhaoceefbeorfnyreyaecovttftriiiwecnngaoagaadlvtteaiihrugosetiandhtsaeoiei.nrosqdsnu,deTienfhttacihhlieseett HsArazeyhnipdSodmrerwoupaondtltgsuheorocm,naebptep1hhtr9peih4.ec01C4,9otO75naf8a2tfb-nriu9dcol,elalHrffe.orrmOroa.omptfet2Hre4H.m9r.Oi,M.ss.sSh2ito1aoS4wrnt,natTtToaoiabnobrlnleepeepsprsr.yfoood4fOr7ufC4fcAoi-eicm7ret.phuNfMeato.vretidapgDbeaAaurtlvlmitaiioirdstnu,ssmdioae1ont9na.t4ne7tdr,o 1Mr. Doigdied shortly before the publication ofthe book. PREFACE TO SECOND EDITION INTRODUCTION In the preparation of this second edition advantage has been taken A GENERAL VIEW OF THE UNIVERSE of a number of suggestions made by reviewers and correspondents. The Index has beenenlarged, andan additional chapterhas been added dealing with the identification of the stars and planets; this BY M. DAVIDSON, b.a., d.sc, f.r.a.s. chapter also includes anumber ofstarmaps to supplement those on President ofthe British Astronomical Association, 1936—8 theend-papers. A numberofextraAppendiceshavebeen inserted, many of which deal with developments in astronomy since the THE first chapter gives ageneral survey of the solar system, appearance of the first edition. starting with the Sun which, on the model suggested by M. Davidson. Mr. M. B. B. Heath, is taken as two feet in diameter (its 1954- actua—l diameter is about 860,000 miles). On this scale the planet Pluto so far as we know at present the most distant from — the Sun of the nine planets is nearly if miles away at its average distance. On the same scale the nearest star is about 10,000 miles away. It is easy enough to visualize a di—stance of a fewmiles, andthose who do —a lot of travelling by road drivers of motor vehicles, for instance can form a rough idea of distances of hundreds of miles, but distances of thousands of miles are much more difficult to visualize. When we come to millions of miles it is quite impossible to form any conception ofsuch distances, and asthese figureswould be necessary in dealing with our Galaxy 1 if we started with the Sun two feet in diameter as the basis, a different method will be adopted in this chapter. We shall start with our Galaxy and assume that it has a diameter of 1,000 miles, which is more than twice the distance from Berwick to Land's End. We shall antici- pate what is fully described in Chapter VIII by saying that all the starsyou can see with the nakedeye lie in our Galaxy, and although you can see only a few thousand of these there are about 100,000 million altogether. Suppose that the Galaxy, which is shaped somewhat like a bun,2 has its longest diameter 1,000 miles and its shortest diameter 160 miles; this is like a very flattened bun, six times as long as it is deep, but even this does not give an adequate representation of the 1Seepage346. 2Thisis only a provisional conception. Seepage 348. xiv XV XVI INTRODUCTION INTRODUCTION XV11 — Galaxy because the 'bun' rapidly tapers off so that towards its What lies outside this bun in other words—our Galaxy? The edges its depth is only—about 30 to 60 miles. Having formed a answer is other galaxies more or less of similar shape in many cases mental picture of this and it may not be very easy —for many and some of themabout the same size asour Galaxy, thoughmany readers to do so but it is the best that we can suggest now let of them are much smaller. One of the largest of these, visible to us look at what lies in the interior of the bun. (See Fig. 112 and the naked eye in the northern hemisphere, is the Great Nebula in Plate XXXVIII, Chapter VIII.) Andromeda.1 On the adopted scale it would be about 8,000 miles Imagine that inside the bun there are about 100,000 million tiny away, and although several are known to be nearer to us than this, specks, eachonewithanaveragediameterten-thousandthpartofan there are hundreds of millions of others incomparably more distant. inch, and that they are all moving round the central portions with The 200-inch telescope at Mount Palomar can photograph galaxies various velocities. Fix your attention for the present on one of more than a thousand times as far away as the Great Nebula in these specks which is about 300 miles from the centre of the bun; Andromeda, which would imply on our scale more than 8 although it would be invisible to the naked eye a microscope million miles. Now turn yourattentionfor a momenttothisscale. magnifying a thousand times would show it as a tiny sphere We startedwiththe Earth's diameter as one-millionth of an inch, apparently about one-tenth of an inch in diameter. This speck is in other words, by placing side by side a million specks like that our Sun andon closerexamination youwouldsee anumber ofmuch describedearlier, each speckrepresenting the Earthwitha diameter smaller specks revolving around it, but of course an ordinary of nearly 8,000 miles, we arrive at galaxies of stars more than microscope would be useless for observing these, and you would find 8 million miles away. Perhaps this will enable readers to it necessary to use an electron microscope. These very minute appreciate betterthe magnitude of the universe than tobe told that — specks—muchsmallerthan themain speck aretheplanets,andthe there are external galaxies a thousand million light-years distant. one at greatest distance is two-fifths of an inch away, but of more The explanation of this term appears elsewhere.2 interest than Pluto is another speck at one-hundredth of an inch This brief survey of the universe should enable readers to gain a from thecentralone. ThisisourEarthwhich, onthescale adopted, clear perspective of the problems confronting the astronomer. is about one-millionth of an inch in diameter. It happens to be Formidable as they may seem to be when such immense distances so situated that something we call life has been able to develop on are to be plumbed from his speck representing the Earth, neverthe- it and to survive so far because the heat and light from the Sun less he has succeeded in unravelling many of the secrets of the are favourable for this, but how far they are favourable for the universe, but many still remain unsolved. same purpose on the other specks is largely a matter of conjecture. Some may want to know what lies between all these galaxies of Having formed a mental picture of the Galaxy, now let us turn stars which are separated from one another by such immense to the distances between the specks composing it. In the first distances. The answer is that it is not isolated stars which do not chapter it is shown that, adopting a model of the solar system with belong to any galactic system but are wandering about on their the Sun two feet in diameter, the nearest star is 10,000 miles away, own; such stars do not seem to exist. All the stars in the universe and this could be taken as a fair representation of the distances appear to belong to some galactic system, and outside this and between any one star and its nearest neighbour. On the present between it and the next system there is—nothing but scattered scale, however, where the Sun is a microscopic object, its nearest molecules and atoms of various elements sodium a—nd hydrogen neighbour is about 80 yards away. You can, therefore, form a especially, but many other elements are represented and cosmic picture of a very minute speck representing the Sun and another dust. Although these molecules, atoms, and cosmic dust are so minute speck representing the nearest star separated by 80 yards, scattered that the most perfect vacuum that can be produced on and about 100,000 million more occupying a space like a bun 1,000 Earth is incomparably more dense than is found in interstellar miles long and 160 miles in depth. This is a picture of the Galaxy. 1 See page 320. 2Seepage 290.
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