This page intentionally left blank Turn Left at Orion A hundred night sky objects to see in a small telescope — and how to find them Third edition Guy Consolmagno VaticanObservatory,TucsonArizonaandVaticanCityState Dan M. Davis StateUniversityofNewYorkatStonyBrook illustrationsby KarenKotashSepp,AnneDrogin,andMaryLynnSkirvin CAMBRIDGEUNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521781909 © Cambridge University Press 1989, 1995, 2000 This publication is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published in print format 2000 ISBN-13 978-0-511-33827-4 eBook (NetLibrary) ISBN-10 0-511-33827-9 eBook (NetLibrary) ISBN-13 978-0-521-78190-9 hardback ISBN-10 0-521-78190-6 hardback Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. How Do You Get to Albireo? .............................4 How to Use This Book .......................................6 Contents The Moon.........................................................12 Lunar Eclipses Worldwide, 2004–2020...........................23 The Planets ......................................................26 Approximate Positions of the Planets, 2004–2019..........28 When to See Mercury in the Evening Sky, 2004–2019 ....29 Oppositions of Mars, 2003-2020.....................................29 Seasonal Objects: Winter.................................38 Open Clusters ..................................................................45 Diffuse Nebulae ...............................................................51 Planetary Nebulae...........................................................59 Seasonal Objects: Spring.................................72 Galaxies...........................................................................87 Globular Clusters............................................................91 Seasonal Objects: Summer ............................100 Red Giants .....................................................................107 Seasonal Objects: Autumn.............................152 Southern Hemisphere Objects .......................180 How to Run a Telescope.................................202 While you’re waiting for the clouds to clear..................202 When you go out to observe...........................................205 Storing and maintaining the telescope ..........................207 Computers and the amateur astronomer.......................208 Where Do You Go From Here?......................210 Glossary.........................................................212 Tables .............................................................214 Index ..............................................................220 Acknowledgments ..........................................224 What, Where, and When Table ......................................224 4 TurnLeftatOrion AwhilebackIspentacoupleofyearsteachingphysicsinAfrica,asavolunteerwiththeUS PeaceCorps.AtonepointduringmyserviceIhadtoreturntotheUSforamonth,andwhile IwashomeIvisitedwithmyfriendDan,whowaslivingatthetimenearNewYorkCity. WegottotalkingaboutthebeautifuldarkskiesinAfrica,andtheboundlesscuriosityof mystudentsaboutthingsastronomical…andsothatafternoonwewentintoManhattanand, withDan’sadvice,IboughtalittletelescopetotakebackwithmetoKenya. DanwasfarmoreexcitedaboutmypurchasethanIwas.He’dbeenanavidamateur astronomersincehewasalittlekid,somethingofanachievementwhenyou’regrowingupin thegrimierpartsofYonkersandyoureyesightissobadyoucanstartfireswithyourglasses. AndhewasjustdroolingoversomeofthethingsI’dbeabletoseeinAfrica. Ididn’treallyunderstandit,atfirst.Yousee,whenIwasakidI’dhadatelescope,too,a little2"refractorthatIhadboughtwithtradingstamps.IrememberedlookingattheMoon; andIknewhowtofindJupiterandSaturn.Butafterthat,Ihadsortofrunoutofthingstolook How Do at.Thosegloriouscolorpicturesofnebulaethatyouseeintheglossymagazines?They’reall takenwithhugetelescopes,afterall.Iknewmylittletelescopecouldn’tshowmeanything likethat,evenifIknewwheretolook.AndofcourseIdidn’tknowwheretolook,anyway.So thattelescopehadgathereddustinacloset;eventuallyitgotpassedontomynephewsand You Get to wasneverseenagain. AndnowherewasDangettingallworkedupaboutmynewtelescope,andthethought thatI’dbetakingitbacktoAfrica,landofdarkskiesandsouthernstarshehadneverbeenable Albireo? tosee.Therewereplentyofgreatthingstolookat,heinsisted.Hegavemeastaratlas,anda pileofbookslistingdoublestarsandclustersandgalaxies.CoulditbethatIcouldreallysee someofthesethingswithmylittletelescope? Well,thebookshegavemewereabigdisappointment.Atfirst,Icouldn’tmakeheadsor tailsoftheirdirections.AndevenwhenIdidfigurethemout,theyallseemedtoassumethat Ihadatelescopewithatleasta6"mirrororlens.Therewasnowayoftellingwhich,ofallthe objectstheylisted,Imightbeabletoseewithmylittle3-incher. Finally,Danwentoutwithmeonenight.“Let’slookatAlbireo,”hesaid. I’dneverheardofAlbireo. “It’sjustoverhere,”hesaid.“Pointitthisway,zip,andthereyouare.” “Neat!”Isaid.“Adoublestar!Youcanactuallyseebothofthem!” “Andlookatthecolors,”hesaid. “Wow...oneofthem’syellow,andtheother’sblue.Whatacontrast.” “Isn’tthatgreat?”hesaid.“Nowlet’sgoontothedouble-double.” Andsoitwentforthenexthour. Eventuallyitoccurredtomethatallofthebooksintheworldweren’tasgoodashaving afriendnexttoyoutopointoutwhattolookfor,andhowtofindit.Unfortunately,Icouldn’t takeDanbacktoAfricawithme. Isuspecttheproblemisnotthatunusual.Everyyear,thousandsoftelescopesaresold, usedonceortwicetolookattheMoon,andthentheywindupgatheringdustintheattic.It’s notthatpeoplearen’tinterested–butonanygivennighttheremaybe2,000starsvisibleto thenakedeye,and1,900ofthemareprettyboringtolookatinasmalltelescope.Youhaveto know where to look, to find the interesting double stars and variables, or the nebulae and clustersthatarefuntoseeinasmalltelescopebutinvisibletothenakedeye. Thestandardobserver’sguidescanseemjustincomprehensible.Whyshouldyouhave tofightwithtechnicalcoordinatesystems?AllIwantedtodowaspointthetelescope“up” somenightandbeabletosay,“Hey,wouldyoulookatthis!” It’sforpeoplewhoarelikeIwaswhenIwasstartingout,thecasualobserverswho’dlike tohavefunwiththeirtelescopeswithoutcommittingthemselvestohoursoftechnicaldetails, thatwedecidedtowriteTurnLeftatOrion. GuyConsolmagno(Easton,Pennsylvania;1988) HowDoYouGettoAlbireo? 5 IntroductiontotheThirdEdition:AlothashappenedinthefifteenyearssinceDanfirst showedmeAlbireo.Backthen,wewouldhavetotip-toewhencominginlate,soasnotto wake up his kids; Dan and Léonie’s babies are teenagers now. In 1983 I had given up a researchjobatMITtojointhePeaceCorps;in1989,IgaveupaprofessorshipatLafayette CollegetoentertheJesuits.I’mdoingfull-timeresearchagain…andstilltraveling. Ialsostillhavemy90mm’scope.ButnowIgettoobservewiththeVaticanObservatory’s AdvancedTechnologyTelescopeonMt.Graham,Arizona–a1.8mreflectorwhoseoptics andcontrols(includingtheworld’sfirstlargespin-castmirror)aretestbedsforthetelescopes ofthetwenty-firstcentury.Dan,moremodestly,hasupgradedtoaSchmidt–Cassegrain8". It’snotonlyourpersonallivesthathavechangedsince1984.Inthelastfifteenyears, majordevelopmentshaveoccurredinamateurastronomy. Personalcomputers,andtheastronomysoftwarethatrunsonthem,havechangedthe waymostofusfindobjectsinthenighttimesky.Wecantapafewkeysanddiscoverwhat starswillbeupatanygivenmoment.Moreimportantly,itdoesn’ttakemuchworktoenter theorbitsofcomets,asteroids,andtheouterplanetsandprintoutcustomizedfindercharts.In fact,youcanbuyacomputer-controlledtelescope;justpunchinsomenumbers,andthe’scope slewsitselftothepre-programmedobject.Withallthisconvenience,whoneedsabook? Amateurtelescopeshavechanged:theDobsoniandesignhasput6"or8"mirrorsinthe pricerangeofnearlyeveryone.Meanwhile,computer-controlledproductiontechniqueshave madesmallSchmidt–Cassegrainsbetterthanever,whileholdingthelineonprices.Sowhy settleforasmallthree-incheranymore? Andfinally,ifyoureallywanttoseespectacularastronomicalsightsyoucanjustlogon totheInternetanddownloadsomeHubblepictures,orcheckoutthelatestspacecraftimages. So,forthatmatter,whoneedsatelescopeatall? Andyet...therewewerelastnight,outinDan’sfrontyard,peeringatdoublestarswith histhirty-year-old2.4"refractor(borrowed,withpermission,fromitscurrentteenagedowner). Ourexcusewasthatwewerecheckingoutobjectsforpossibleinclusioninthisnewedition. Therealreasonwasthesheerfunofthehunt.Hurrahforsmalltelescopes! AlltheexcitementofHubbleandthespaceprogramhasnotreplacedamateurastronomy. Rather,ithascreatedanurgeinmoreandmorepeopletogooutandsee“space”forthem- selves.TheimpactofShoemaker–LevyintoJupiterin1994leftspotsintheJovianclouds thatyoucouldseeforyourselfwithathree-incher;anditsimpactonthehumanimagination was just as profound. Since then, comets Hyukatake (1996) and Hale–Bopp (1997) have provedthatnothingbeatsfindingit,andseeingit,foryourself. TheInternetitselfhashadaninterestingeffectonthisbook.We’vegottenanumberof nicereviewsonthe’net.Butreadingwhatpeoplesay,we’vealsolearnedtooursurprisehow theyareusingwhatwewrote.Theyarenotjustamateurswiththree-inchtelescopes.Wefind thatTurnLefthasalsobecomeafavoriteforpeoplewithbinoculars;ausefulintroductionfor Dobsonianusers;andtheguide-of-choiceforbeginnerswith’scopesinthe8"range. Withthatinmind,we’vetakenadvantageofthisneweditiontoincludesomeadditional objects for people with telescopes both slightly larger, and smaller, than ours.We’ve also takenthischancetocorrectsomeofthemoreobviousmistakesandtypos.(Onereviewer, bless his soul, said Turn Leftwas “nearly perfect”; for all that, we’d managed to misspell Betelgeuseeverywhere!)We’vere-orderedsomeofthespreads,andnowindicatethebest monthstoseeagivenobjectinthesky.We’veupdatedtheplanetaryandeclipsetables,of course;andwe’venotednewpositionsfordoublestarsthathavemovedintheirorbitssince thefirsteditioncameout.We’veaddedmanynew“neighborhood”objects.Andafterafew trips far south we couldn’t resist telling you about the southern hemisphere objects that it wouldbeacrimeforanytravellertomiss. Butourbasicphilosophyhasremainedunchanged.Westillassumeyouhaveasmall telescope,afewhours’sparetime,andaloveofthenighttimesky.TurnLeftatOrionisstill thebookIneedbesidemeatthetelescope.We’redelightedthatotherfolkshavefoundittobe afaithfulcompanion,aswell. BrotherGuyConsolmagnoSJ(visitingStonyBrook,NY;1998) 6 TurnLeftatOrion We’veputtogetheralistofourfavoritesmalltelescopeobjects,arrangedbytheseasonswhen they’rebestvisibleintheeveningandtheplacesintheskywherethey’relocated.Inallthese objects,weassumeyouhaveatelescopemuchlikeours:asmall’scope,whosemainlensor mirrorisonly6to10cm(2.4"to4")indiameter.Everythinginthisbookcanbeseenwith suchsmalltelescopesunderlessthanidealskyconditions.Allourdescriptionsofthemare linkedtothewaytheseobjectshavelookedtous. FindingYourWay:Firstofall,youdon’tneedtomemorizetheconstellationsinorderto usethisbook.Constellationsaremerelynamesthatastronomersgivetocertainsomewhat arbitrarilydefinedregionsofthesky.Thenamesareusefulforlabelingthethingswe’llbe looking at; otherwise, don’t worry about them. If you do want to know the constellations, thereareanumberofgoodbooksavailable;onepersonalfavoriteisH.A.Rey’sTheStars. Butfortelescopeobserving,allyouneedisanideaofwherethebrighteststarsare,touseas guideposts.WedescribethelocationofthesebrightestguidestarsinasectioncalledGuide- posts,startingoffeachseasonoftheSeasonalObjects. Starssetinthewest,justliketheSun,soifyou’replanningalongobservingsessionstart byobservingthewesternobjectsfirst,beforetheygettoolowinthesky.Theclosertothe horizonanobjectgets,themoretheatmosphereobscuresanddistortsit,soyouwanttocatch thingswhenthey’reashighupintheskyaspossible.(Theonlyexceptionsareobjectsthatsit How to directlyoverhead.Mosttelescopetripodshavetroublewithaimingstraightup,sotrytocatch themsometimeshortlybeforeoraftertheygettothatpoint.) So how do you decide, on any given night, what objects are up? That’s what the What,Whereand Whenchartatthebackofthebookisallabout.Foragivenmonth,and Use This thetimewhenyou’llbeobserving,itlistseachoftheconstellationswhereseasonalobjectsare located;thedirectionyoushouldturntolookforthatconstellation(e.g.W=west);andifyou shouldbelookinglow,towardsthehorizon(e.g.,“W-”),orhighup(e.g.,“W+”).Constel- Book lations markedwithonlya“++”symbolarerightoverhead.Thenyoucanturntothesea- sonalpagestocheckouttheobjectsvisibleineachconstellationavailablethatnight. TheMoonandthePlanets:ThefirstobjectsweintroduceinthisbookaretheMoonand planets.FindingtheMoonisneveraproblem!Infact,itistheonlyastronomicalobjectthat issafeandeasytoobservedirectlyinbroaddaylight.(Indeed,unlessyou’reupinthewee hoursofthemorning,daytimeistheonlytimeyoucanseethethirdquarterMoon.Tryit!) TherearecertainthingsontheMoonthatareparticularlyfuntolookfor.Also,theMoon changesitsappearancequiteabitasitgoesthroughitsphases.We’veincludedpicturesand discussionsforfivedifferentphasesoftheMoon,plusatableofwhentoexpectlunareclipses, andwhattolookforthen. Whenyoulookdirectlyoverhead,youdon’t havetolookthroughasmuchdirty,turbulent air as you do when you look at something lowonthehorizon.Trytoavoidlookingat thingslowonthehorizon. Stars to the south never do rise very high;there’snothingyoucandoaboutthat. Butstarsalongtheotherhorizonswillap- pearhigherintheskyduringdifferentsea- sons,oratdifferenttimesofthenight. HowtoUseThisBook 7 Thestarsanddeepskyobjectsstayinfixed positionsrelativetooneanother.Butwhich of those stars will be visible during the evening changes with the seasons; objects that are easy to see in March will be long gone by September.Thus we refer to these objectsas“seasonal.”Someobjectsarevis- ibleinmorethanoneseason.Whenwetalk about“winterskies”we’rereferringtowhat you’dseeinthewinterataround9:00p.m. localstandardtime.Ifyouareupat3inthe morningtheskywilllookquitedifferent.The generalruleofthumbistoadvanceonesea- sonforeverysixhours,sospringstarswill bevisibleonwintermornings,summerstars onspringmornings,andsoforth. Planetsaresmallbrightdisksoflightinthetelescope.Evenwitha2.4"telescope(thatis, atelescopewhosemainlensormirroris2.4inchesindiameter)youshouldalsobeableto pickoutquiteabitonandaroundthebrighterplanets.Forexample,youcanseethephasesof Venus,thepolarcapsonMars,thecloudbandsand(sometimes)theGreatRedSpotonJupi- ter,Saturn’srings,andthelargestofthemoonsaroundJupiterandSaturn.Thepositionsofthe planets,relativetotheotherstars,changefromyeartoyear;butifyouknowingeneralwhere tolookforthem,they’reveryeasytofind.They’regenerallyasbrightasthebrighteststars. Wegiveatableofwhentolookforeachplanet,andwedescribelittlethingsyoumightlook forwhenyouobservethem. TheSeasonalObjects:Undereachseason,you’llfindourselectionofobjectsthatare bestseenatthattimeofyear,atabout9o’clockintheeveningintheUS,Canada,Europe, Japan…anywherebetweenlatitudes25°and55°N.Thestars,andallthedeepskyobjectswe talkaboutinthissection,stayinfixedpositionsrelativetooneanother.Butwhichofthose starswillbevisibleduringtheeveningchangeswiththeseasons;objectsthatareeasytoseein MarchwillbelonggonebySeptember. Someobjectsarevisibleinmorethanoneseason.JustbecausetheOrionNebulaisatits bestinthewinterdoesn’tmeanyoushouldriskmissingitinthespring.Someofthenicest objectsfromthepreviousseasonwhicharestillvisibleinthewesternskyarelistedinatable atthebeginningofeachseason. Also,rememberthatwhenwetalkabout“winterskies”,forinstance,we’rereferringto what you’d see in the winter at around 9:00 p.m., standard time. If you are up at 3 in the morningtheskywilllookquitedifferent.Thegeneralruleofthumbistoadvanceoneseason foreverysixhours,sospringstarswillbevisibleonwintermornings,summerstarsonspring mornings,andsoforth. Foreachobject,wegiveitsnameandwedescribethetypeofobjectitis: ADoubleStar lookslikeonestartothenakedeye,butinatelescopeitturnsouttobe two(ormore)stars.Thatcanbeasurprisingandimpressivesight,especiallyifthestarshave differentcolors.They’realsogenerallyeasytolocate,evenwhentheskyishazyandbright. Eachdoublestardescriptionincludesalittletabledescribingtheindividualstars,theircolors andbrightness,andhowclosetogether(inarcseconds–seetheglossary)theyappeartobe. Variablestarsvarytheirbrightness;wedescribehowtofindafewthatcanchangebright- nessdramaticallyinamatterofanhourorless. AnOpenClusterisagroupofstars,oftenquiteyoung(byastronomicalstandards),that areclumpedtogether.Viewinganopenclustercanbelikelookingatahandfulofdelicate, twinklingjewels.Sometimestheyaresetagainstabackgroundofhazylightfromtheunresolved