1910Ap J 31 8B hm0/ f ji559—182o very fewstars.Theextensionsofthisgreat nebulareachto,and are athindarklaneandnarrowstripofbrighternebulosity.These ing places(for1855.0): near theedgeofplate.Thediscoverythisobjecttherefore in thenebula,isnotdue toachancevacancy.Thelineofdemarka- two starsarejoinedto—19?4357,whichisitselfnebulous,byathin nebulous massinwhichonthenorthfollowingsideclosetostars In itsfainterportionsitinvolvestothesoutheaststarsB.D. noticed ontheWillardlensphotograph,whereitwasveryfaintand thinning outordimmingofthestarsinthisregion, thatareapparently in afeeblemannerconnectwith,thegreatnebula ofpOphiuchi. cially isthisnoticeableatitsnorthernandwestern end,nearthestars is duetothesmalllanternlens. also attachedtotheWillardmounting)showedaremarkablenebula it seemstoshowaveilingofthestarsincertain of itsportions.Espe- involving the4.5magnitudestarvScorpii(PlateI).Ithadnotbeen following theseobjectsaredarkregionswhere thereareapparently in 1893,theplateswithsmalllanternlens(iiinchesdiameter, thread ofnebulositywhichiswellshowninPlateIIA.Northand — i7?45ii,—17?4502,and--i8?424o.Itis quite evidentthatthe (which IhadfoundwiththeWillardlens)atLickObservatory ON AGREATNEBULOUSREGIONANDTHEQUES- TION OFABSORBINGMATTERINSPACEANDTHE © American Astronomical Society •Provided bytheNASA DataSystem i9?4357, —19?4359,and—i9?436i.Thelasttwoareinadense The greatestinterestinthisnebula,however, lies inthefactthat Roughly thisnebulaisboundedbythefigureformedfollow- While photographingtheregionofgreatnebulapOphiuchi TRANSPARENCY OFTHENEBULAE 16 —1850 16 10—2100 16 4—18o and By E.BARNARD a S 8 PLATE I © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem

Gkeat Nebula of Nu SCORPll io-Inch Lens. 1905, April 4, içh 25™ to 24h 2om G. M. T. Scale: i° = 37 mm The plate covers 3?9X3?i 1910Ap J 31 8B 0 ance duetoanactualthinningoutofthestars.Itlooks,wherethis and suddenlydrawnbytheedgesofnebulatoassumeappear- This remarkablefeatureofthenebulaisveryimportanttoaproper part ofthenebulaspreadsout,asiffainterstarswerelost,and tion betweentherichandpoorportionsofskyhereistoodefinitely understanding oftheregiongreatnebulapOphiuchi,which is fivedegreessouthofvScorpii.IntheregionpOphiuchithere nebula istransparentornot.Theassumptionhasalwaysbeenthat nebula. Atpresentwehavenomeansofdeterminingwhethera of thestarsisnotsoclearlyevidentasincasevScorpii of thenebula,butfromitscomplicatedandirregularformhiding is everyappearanceofablotting-outthestarsbyfainterportions the brightnessofothersreducedatleastamagnitudeormore. proof withrespecttothenebulae.Ithinkinpresentcase, of cometsiseasy,butforobviousreasonstherecanbenosimilar lead totheaboveconclusion. at thispoint.Thisfact,unfortunately,isnotsoevidentintherepro- however, thatthenebulaofvScorpiiisshowntobeatleastpartially they aretransparentlikethecomets.Theproofoftransparency duction asitisintheoriginal,aninspectionofwhichwouldatonce must beconsiderable.Thepictureisquiteconclusiveevidence Scorpio, Libra,andLupus,isintendedtoshow therelationofthese describes averyintricateandstragglingnebulainthisregion,con- be found,withmoresensitiveplatesandlongerexposures,tocon- necting thestarsttandSScorpii.Ibelievethisobjectwillultimately paper ofmineinAstrophysicalJournal,23,144,March1906,which that thenebulaisnearertousthangeneralbackgroundofstars transparent, buttheabsorptionoflightstarsbehindit panying chart,whichcoverspartsoftheconstellationsOphiuchus^ necte withthevScorpiiandpOphiuchinebulosities.Theaccom- nebulosities, especiallyinthecaseofpOphiuchi, forthatnebula all thisregion.Ihaveindicatedonlythebrighter portionsofthese various nebulositiestoeachother.Thereis strongevidencethat and canbetracedforatleast5ina6J° inS.IndeedIam extends inastronglymarkedmannerforsome distancetotheeast they arebutthebrighterpartsofoneenormous nebulathatcovers © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem In connectionwiththepresentsubjectIwouldcallattentiontoa A GREATNEBULOUSREGION9 1910Ap J 31 8B © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem parts ofthenebulafairlywell.Thedarklanes whichruneastward nature andthatofthesurroundingregion.The reproductionfalls convinced thatallthisregionasfareast6Ophiuchiandbeyond far shortofdoingjusticetothissubject,though itshowsthebrighter it. Itisimpossibleadequatelytodescribeindetail itsextraordinary is affectedwiththisdiffusednebulosity. respects ithasadeeperinterestbecauseofthe aspect oftheskynear sky. EvenincomparisonwiththegreatnebulaofOrionsome v Scorpii.IndeedIdonotthinkthereisafinernebulaintheentire io E.BARNARD The pOphiuchinebulaisfarmoreremarkablethanthatof Chart oftheGreatNebulousRegion 1 91 OAp J 31 8B 11mmm io-Inch Lens.1905,April5,1945™to24i5G.M.T.Scale:i°=i6.7 Great NebulousRegionofRhoOPHIUCHI The platecovers7^7X7?7 PLATE IIA N © AmericanAstronomicalSociety•ProvidedbytheNASAAstrophysicsDataSystem 11mmm io-Inch Lens.1905,June3,17oto21G.M.T.Scale:i°=i3.5 hra Plates overlapslightly.Centerofplateata=i645,522°South Extension ofVacantLanestowardtheEast The platecovers7?6X6?7 PLATE IIB N 1910Ap J 31 8B 0 7 in theextremeupperright-handcornerofPlate IIAisduetothe or 19mm(i8')tothewestofthesestars.Part oftheillumination I. Italsoshowsaportionofthenebulav Scorpiiaboutfinch nebulous starswhicharenearthelowerleft-hand comerofPlate nebulosity extendtoandbeyondAntares,diffùsing asfarsouth a humaneye,fromwhichfactIhavecalledit “the eye.”Wavesof around thestar.Thisstarandnebulousstripssingularlyresemble .Atitsupperedgethisplate(Plate II A)showsthethree diverging stripsofnebulosity,thenorthernandupperstripcurving assumes abeautifulribbedappearancewhichisbutfeeblyrepre- sented inthehalf-tone.Thestar22Ophiuchiliesbetweentwo west about30'.Thislastdoesnotseemtocenteratanyparticular lanes runningtotheeast. . Thesecondensationsareseparatedbyanirregulardarkrift pool appearancewhichisformedbythebeginningofvacant 20' to30'long,whichrunsnorthandsouth.Northofpthenebula star pOphiuchi,andtheother,equallyimportant,precedesitto a defect.Immediatelyfollowingthiscondensationisdarkwhirl- being thelongest.Aboutiqnorthandslightlyeastisasingular are eachabout20'or30'long,thetworunningnorthandsouth This presentsaverysingularandstrikingappearance.From equally remarkable,i°duesouthofpatthestarC.D.—24°12684. and whichspreadsinafaintdiffusionforseveraldegreestothesouth. the starasacenterissuefourbrightwhorlsofnebulosity,which In additiontothemaingreatcondensationsthereisanotherone, condensation whichismarkedbyaconsiderableamountofdetail condensations, o-Scorp'Uisinvolvedinaverystrongandirregular which vacantlanesextendfartotheeast.Besidestwomain is locatedinaholeverydensepartoftheMilkyWay,from impossible tobringthemout,inthehalf-tone.Thepictureshows, main portionsofthenebula.Toallappearance,greatnebula however, thestrikingabsenceofstarsinspaceoccupiedby importance asthebrightportionsofnebula,butithasbeen U-shaped darkmarkingthatissodistinctastoappearalmostlike one ofthetwo.Tomethesesingulardarkfeaturesareasmuch from itcontainverystrikingblackmarkings,especiallythenorthern © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The twomainandlargestcondensationslie,one,aboutthetriple A GREATNEBULOUSREGIONn 1910Ap J 31 8B 0 0 reproduction. TheportionofthegreatvScorpiinebulawhichis from theupperedge.Therestinthiscornerisunreal. 0.9 inchfromtheright-handouteredgeofblockand1.1inches diffused nebulositysouthofAntaresisrelativelytoobrightinthe shown atthispointisreadilymadeout(becauseofitsgreatintensity; p Ophiuchi,andothers,itsconnectionwiththesubstratumof black, irregular,andsharplydefinedriftsperforationswhich nection ofthisgreatnebulawithsuchbrightstarsascrScorpii, extending westandsouthfromitforabout6'.Thisisnoticeableon covery ofthisgreatnebulousregionseePopularAstronomy,5,227, overlaps PlateIIA.Itsedgesareveryclearlydefinedforabout east. Thelowerorsouthernofthese,whichisbroad,thestrongest 0.25 incheastof22Scorpii.Ithasanarrowstripnebulosity half-tone, thoughitisreal. the photographsofregion0Ophiuchi{Astrophysical Journal, with thepOphiuchinebula,andwhichareso wonderfully shownon holes areduetoabsorbingmediabetweenus andtheMilkyWay, connection withthesmallstarsisonlyapparent andthelanes part ofthesky,andhencerelativelysmallbodies. If,however,the Milky Wayatthispointandelsewhere.Thismustnecessarilybe of theactualsmallnessstarsforminggroundwork small starsoftheMilkyWay,inwhichlanesoccur,wasaproof September 1897. unfortunately arelostinthereproduction.Forahistoryofdis- of thetwomostconspicuouslanesismarkedforabout2withvery east inanirregulargroupofsmallholes.Thenorthernandshorter marked. ItsfullextentisbeautifullyshowninPlateIIB,which the vacantlanesorstreams,previouslyreferredto,extendingto Plate IIA. 12 E.BARNARD that thesmallstarsareroughlyasneartouslargeonesinthis true, fortheconnectionwithbrightandsmallstarswouldimply the suppositionofsmallnesswouldnotholdtrue. 7, afterwhichitbecomesbrokenandshatteredendsio°tothe © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem While speakingofthesestrangedarkforms,such asareconnected Among themostremarkablefeaturesofthismarvelousregionare The starn(whichisC.D.--24?i2098)0.41inchnorthand I haveatothertimescalledattentiontothefactthatrealcon- 1910Ap J 31 8B a to theeastfrom“theeye”onPlateIIAandcontinued inPlateIIB Solar ObservatoryoftheCarnegieInstitution onMountWilson, inch BrashearlensoftheBrucephotographicdoublet which,through runs almostdueeastandwest.Whileatthe LickObservatory, California, in1905. the courtesyofProfessorHale,wastemporarily stationedatthe exist intheskyindependentlyofstars. in theConstellationTaurus”AstrophysicalJournal,25,218,April ties Iwouldrefertoapaperofmine,OnNebulousGroundwork of darkabsorbingmatterinspaceconnectionwithvisiblenebulosi- condition ofnebulousmatterorisitsomethingwhollydifferent am acquainted.ItliesinanordinarypartoftheMilkyWayand nebula. Itisroundandsharplydefined.Itsmeasureddiameter' 1907, whereasystemofdarklanesandholesinTaurusisshownto from theordinarynebulosityofsky? out. Itishardtobelieveintheexistenceofsuchmatterona for incertainpartsoftheskystarsareapparentlyentirelyblotted us andthestars—andImustconfessthattheirlookstemptoneto is notduetothepresenceorabsenceofstars,butseemsreallybea It isasmallblackholeinthesky,verymuchlikeplanetary tremendous scaleasisimpliedbythephotographs.Astoitsnature this belief—suchmattermust,inmanycases,beperfectlyopaque, marking ontheskyitself. on thenegativeis2'6.Thepositionclosely: on anumberofmyphotographsforthepastfifteenyearsormore. call specialattentiontoanobjectofthisclasswhichhasbeenshown 9, 157/1899,andPopularAstronomy,14,579,Dec.1906)/!would find theminmostcasestobeintimatelyconnected.Isitanultimate if itdoesexist,mustinsomewayberelatedtothenebulae,forwe is perhapsthemostremarkableofallblackholeswithwhichI On accountofitssharpnessandsmallnessisolation,this © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem As willbenoticedinthephotographsgreat laneextending The accompanyingphotographsweremadebymewiththe10- To thosewhomaybeinterestedinthesubjectofpossiblemasses If thesedarkspacesoftheskyareduetoabsorbingmatterbetween hms0 A GREATNEBULOUSREGION13 1875.0 a==i8253i,S=-2Ó9'. I4 E. E. BARNARD

I once showed a plate of this region to Professor Tucker, who had such a large part in the making of the Cordoba . He said that this picture made clear an experience in his observing work at Cordoba that had always been a puzzle to him. One night he had set his telescope in the region a little north of and prepared to record the transits of as they passed through the field. Presently no stars came into the field of his telescope. After watching for some time he finally concluded the sky had clouded over, but on looking out he found it perfectly clear. He returned and watched a long time before any stars appeared. His telescope had been pointed to this lane and nothing but blank sky had passed.

LIST OF STARS REFERRED TO ON THE CHART Bonner Durchmusterung, 1855.0

No. Mag. b 180 4240 i6h om 39.sI 18° 36 c 17 4502 16 i 34-4 17 57 v Scorpii. ïQ 4333 16 3 33-9 19 4 d Ï7 4511 16 3 40.6 17 51 e 21 4^on; 16 5 9.4 21 i / 20 4444 16 5 56.9 20 43 g 20 4454 16 8 26.8 20 56 h T9 4357 16 ro 38-3 19 51 !9 4359 16 11 36.3 19 41 I 19 4361 16 12 0.8 19 45 t/' Ophiuchi = m. 19 4365 16 15 37-3 19 4

Cordoba Durchmusterung, Epoch 1875.0

No. Mag. X Lupi ■33 io754 i5h 43n i?8 33 14-7 Tr Scorpii., ■25 11228 15 51 18.0 25 45-3 8 Scorpii.. •22 11292 15 52 57-1 22 16.2 13 Scorpii. •27 10841 16 4 36.6 27 35-7 I 1

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