Turn Left at Orion : A hundred night sky objects to see in a small telescope - and how to find them

226 Pages·2000·5.83 MB·English

by  Davis

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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-13 978-0-511-33717-8 eBook (EBL)
ISBN-10 0-511-33717-5 eBook (EBL)
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
8 TurnLeftatOrion
membersofthecluster.Onagooddarknight,thiseffectcanbebreathtaking.Wediscussopen
clustersinmoredetailwhenwetalkabouttheclustersinAuriga,onpage45.
Galaxies, Globular Clusters, and the various types of Nebulae will all look like little
cloudsoflightinyourtelescope.AGalaxyconsistsofbillionsofstarsinanimmenseassem-
blage,similartoourownMilkyWaybutmillionsoflightyearsdistantfromus.Itisastonish-
ingtorealizethatthelittlesmudgeoflightyouseeinthetelescopeisactuallyanother“island
universe”sofarawaythatthelightweseefromanyofthegalaxiesthatwetalkabout(except
theMagellanicClouds)leftitbeforehumanbeingswalkedtheEarth.Wediscussgalaxiesin
greaterdetailonpage87(withtheWhirlpoolGalaxy,M51).
AGlobularClusterisagroupofhundredsofthousandsofstarswithinourowngalaxy,
boundtogetherforeverinadenselypacked,sphericalswarmofstars.Onagoodcrispdark
night,youcanbegintomakeoutindividualstarsinsomeofthem.Thesestarsmaybeamong
OpenCluster:M37 theoldestinourgalaxy,perhapsintheuniverse.Onpage91(M3inCanesVenatici)wego
intothetopicofglobularclustersingreaterdetail.
DiffuseNebulaearecloudsofgasanddustfromwhichyoungstarsareformed.Though
theyarebestseenonverydarknights,thesedelicatewispsoflightcanbeamongthemost
spectacularthingstolookatinasmalltelescope.Seepage51(theOrionNebula)formore
informationonthesenebulae.
PlanetaryNebulae(whichhavenothingtodowithplanets)arethehollowshellsofgas
emittedbysomeagingstars.Theytendtobesmallbutbright;some,liketheDumbbelland
theRingNebulae,havedistinctiveshapes.Wetalkaboutthemingreaterdetailonpage59
(theClownFaceNebulainGemini).Ifthedyingstarexplodesintoasupernova,itleaves
behindamuchlessstructuredgascloud.M1isasupernovaremnant;seepage47.
Nextwegivetheofficialdesignationoftheseobjects.Catalogsandcatalognumbers
can seem to be just as confusing as constellations, at first. But these are the methods that
Galaxy:TheWhirlpoolGalaxy everyoneusestoidentifyobjectsinthesky,soyoumayaswellgettoknowthem.Sometimes
it’sfuntocomparewhatyouseeinyourtelescopewiththeglossycolorpicturesthatappearin
astronomymagazines,wheretheseobjectsareoftenidentifiedonlybytheircatalognumber.
StarsaredesignatedbyGreeklettersorArabicnumerals,followedbytheLatinnameof
theconstellationthey’rein(inthegenitivecase,forthebenefitofLatinscholars).TheGreek
lettersareassignedtothebrighterstarsinthe(veryapproximate)orderoftheirbrightness
within their constellation. For example, Sirius is also known as Alpha Canis Majoris (or
Alpha CMa for short) since it’s the brightest star in Canis Major, the Big Dog. The next
brightest are Beta, Gamma, and so on. Fainter naked-eye stars are known by their
FlamsteedNumber,e.g.61Cygni, assignedbypositionwesttoeastacrosstheconstellation.
Subsequentcatalogs(withavarietyofnumberingschemes)havefollowed,butmostoftheir
starsaretoofainttobeofinteresttous.
Doublestarsalsohavecatalognumbers.FriedrichStruveandSherburneBurnhamwere
twonineteenthcenturydoublestarhunters;doublesthatfilledtheircatalogsnowbeartheir
GlobularCluster:M3
names.Variablestarsaregivenletters.ThefirstknownineachconstellationwereletteredR
throughZ;asmorewerediscoveredadouble-letteringsystemwasintroduced:e.g.VZCancri.
Forclusters,galaxies,andnebulae,twocatalogsusedinthisbookaretheMessierCatalog
(withnumberslikeM13)andtheNewGeneralCatalog(withnumberslikeNGC2392).Charles
Messierwasacomet-hunterinthe1700swhohadnouseforgalaxiesandnebulae.Hekept
findingthemoverandoveragain,andgettingconfusedbecausemanyofthemlookedlike
comets.Sohemadealistofthem,tolethimknowwhatnottolookatwhilehewassearching
forcomets.Intheprocesshewoundupfindingandcataloguingmostoftheprettiestobjects
inthesky.Buthemanagedtonumbertheminatotallyhaphazardorder. TheNewGeneral
Catalog,whichdatesfromthenineteenthcentury,numbersobjectsfromwesttoeastacross
thesky.ObjectsthatyouseeinthesameareaoftheskyhavesimilarNGCnumbers.
Foreachobjectweprovidearating,andlisttheskyconditions,eyepiecepower,andthe
Diffusenebula:TheOrionNebula bestmonthsoftheyeartolookforthem.
Theratingisourownhighlysubjectivejudgementofhowimpressiveeachobjectlooks
inasmalltelescope.