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On Cas A, Cassini, Comets and King Charles Roberto SoriaA, Riccardo BalestrieriB, and Yasuyo OhtsukaC AInternational Centre for Radio Astronomy Research, Curtin University,GPO Box U1987, Perth, WA 6845, Australia. Email: [email protected] BVia G. Giacomini 87/14, 47890 Citta`, RepubblicaSan Marino 3 CBritish Library,96 Euston Road, London NW12DB, UnitedKingdom 1 0 2 Abstract: Were-examinethelong-standingproblemofthedateoftheCassiopeia Asupernova(SN), n inviewofrecentclaimsthatitmightbethe1630“noon-star”seenatthebirthofKingCharlesII.We a do not support this identification, based on the expected brightness of a Type-IIb SN (too faint to be J seen in daylight), the extrapolated motion of the ejecta (inconsistent with a date earlier than 1650), 3 the lack of any scientific follow-up observations, the lack of any mention of it in Asian archives. The 2 origin of the 1630 noon-star event (if real) remains a mystery; there was a bright comet in 1630 June but no evidence to determine whether or not it was visible in daylight. Instead, we present French ] reportsabouta4th-magnitudestardiscoveredbyCassiniinCassiopeiainorshortlybefore1671,which h was not seen before or since. The brightness is consistent with what we expect for theCas A SN; the p date is consistent with the extrapolated motion of the ejecta. We argue that this source could be the - t long-sought SN. s hi Keywords: History and philosophy of astronomy — Atlases — Supernovae: general — Supernovae: . individual: Cas A s c i s 1 Introduction reviewed journals yet) byBritish astronomer DrMar- y tinLunnandAmericanhistorianDrLilaRakoczy,and h The youngsupernova remnant (SNR) Cassiopeia A is has become a topic of discussion also among the ed- p oneofthebest-studiedobjectsin thesky,at allwave- ucated public of amateur astronomers: the possibility [ lengths; however, the exact date of the SN event, as thatCasAwasthe“noon-star”allegedlyvisibleinthe 2 well as the nature of the progenitor, are still intrigu- skyonthebirthdayofthefutureBritishkingCharles v ingly unsolved problems. Finding reliable 17th cen- II(1630 May29in theJulian calendar,corresponding 5 tury evidence of visual observations would constrain to June 8 in theGregorian calendar). 5 the peak brightness of the event and hence test the Moreover, over the last few years, ice core records 8 currently favoured scenario of a relatively faint Type from Antarctica and Greenland have been studied in 1 IIb (Krause et al. 2008), based on the spectral study search of fossil records of impulsive ionization events 1. of scattered light echos. It would also help modelling (Dreschhoff & Laird 2006; Dreschhoff & Zeller 1990). 0 the expansion and deceleration of the ejecta, and the As suggested by Rood et al. (1979), γ-rays from SNe 3 propermotionofthecompactobject(Fesen et al.2006; can reach the polar stratosphere and ionize nitrogen 1 Thorstensen et al. 2001). and oxygen, which will then combine to form nitrate : Historians have long debated the possibility that ions(NO−). Suchnitrateswillultimatelybedeposited v 3 Cas A was the mysterious star “3 Cas” observed by in thin layers of polar ice (Zeller & Dreschhoff 1995). i X John Flamsteed on 1680 August 26 (Gregorian calen- Two nitrate peaks in the Greenland ice core record dar), with arguments in favour of this identification were interpreted as signatures of Tycho SN 1572 and r a (eg, Ashworth 1980) because their locations are quite Kepler SN 1604 (Dreschhoff & Laird 2006). In the close and no other star exists there today, or against sameicerecord,only twosignificant nitratespikesoc- it(eg,Stephenson & Green2002;Green & Stephenson curinthesecondhalfofthe17thcentury: onearound 2003; Stephenson & Green 2005a) based on the fact 1667andonearound1700: Dreschhoff & Laird(2006) thatthediscrepancybetweenthepositionof3Casand suggested that either of them could be the signature Cas Aisstill unusuallylarge forFlamsteed’s accurate of Cas A.Otherspikeswere found in thelayers corre- standards. AsStephenson& Green(2005a)pointout, sponding to 1619, 1637, 1639, 1647 (McCracken et al. the10′ discrepancybetween3CasandCasAismuch 2001); no spikes were found for either 1630 or 1680. larger than Flamsteed’s average error of 23′′ for the However,SNidentificationsbasedonnitratespikesre- other 20 stars hecatalogued on thesame night. mainacontroversialtopic(Motizuki et al.2010,2009; In the past couple of years, an alternative sugges- Risbo et al.1981): gamma-ray bursts,soft gammare- tionhasbeenpresentedinseveralinternationalconfer- peaters, magnetar flares and (most importantly) so- ences and press releases1 (unfortunately, not in peer- 4-did-a-supernova-mark-the-birth-of-the-merry-monarch 1See,forexample: and www.ras.org.uk/news-and-press/217-news2011/1948-nam- chandra.harvard.edu/edu/formal/icecore/king charles.html 1 2 Publications of theAstronomical Society of Australia porary writers andpamphleteers(Brown 2010). Lunn & Rakoczy’s argument in favour of a supernova rests strongly on their claim that in 1630 there were no cometsbrightenoughtobevisibleindaylight2. Asim- ilar claim wasconsidered andrefutedbyLynn(1894), who cites a rather obscure Latin chronicle (Giuseppe Ripamonti’sDePeste)describingthescaryapparition of two great comets in 1628 and 1630, which were be- lieved to be responsible for an outbreak of bubonic plague in Milan; both comets are also reported by Kronk (1999),based on thesame source. We examined Ripamonti (1640)’s original Latin text (Fig. 1): Ripamonti does not directly claim to haveseenthe1630comet: hereportstheobservationof the “physician and natural philosopher”3 Alessandro Tadini (1580–1661). According to Ripamonti (p.110), Tadiniwrotethat“the[comet]starhadascaryappear- ance,evenmorethanusual”(“Sydusfuissetruciultra solitum etiam facie”), a popular description that usu- allyreferstothesizeandshapeofacomet’stail. “This hairy star appeared in the month of June: it blazed towards the North, many people saw it” (“Mense Ju- nio [...] extitisse crinitam eam stellam: exarsisse ad Septentrionemspectatoresfuissemultos”). Wechecked a later edition of Tadini’s book (Tadini 1648), which states: “Ahugecomet appearedneartheendofJune, towards the North, and lasted a long time, seen by many people” (“Apparve nel fine del mese di Giugno una Cometa molto grande verso settentrione et duro` moltotempo,vistadapiu`persone”),confirmingRipa- Figure 1: Excerpts from Ripamonti’s book De monti’s account, although “the end of June” is up to Peste,mentioning a brightand(apparently)scary three weeks later than the London sighting. cometvisiblefromMilanin1630June,aroundthe Basedonthoserecords,weagreewithLynn(1894)’s time ofKingCharles’snoon-star. This isthe orig- conclusions that there is good evidence for a bright inal Latin text mentioned in Lynn (1894). cometinthesummerof1630,butcoulditbevisiblein daylight? For that to happen, the head of the comet must have an apparent visual magnitude mv <∼ −6 mag, dependingon the size of the comet head and its lar proton events can also produce nitrate concentra- angular distance from the Sun. Historically, they are tion spikes (Melott & Thomas 2011), and coastal ice rare: weknowoflessthanadozencometsthatreached records may be contaminated by nitrates transported suchbrightness,andcouldbeseenaftersunriseorbe- thorough the troposphere from lower latitudes fore sunset. Most butnot allof themweresungrazing (Motizuki et al. 2010). An argument in favour of a objects (Sauval1997). Forexample,Tycho’s comet in non-solarorigin (includingapossibleSN)forthe17th 1577 was observed before sunset (Kronk 1999), even century nitrate spikes is the low solar activity during theMaunder Minimum (≈ 1645–1715). though it was not a sungrazing object. Hence, Ta- dini’s observation that the comet shone “towards the Given the prominence enjoyed by the noon-star North“ is not inconsistent with a daylight brightness; claim on the NASA/Chandra public outreach website alternatively, it may mean that its tail was pointing andonpopularastronomymagazines,andthecontro- towards the North even though its head was near the versial nature of ice-core nitrate events, we think it is Sun. worth reconsidering this issue. Therefore, in this pa- In conclusion, a daylight comet in the summer of per, we discuss whether the identification of a 1630 1630cannotbeexcluded. TheEnglishrecordsaream- celestial event with Cas A is scientifically plausible. biguousonthenatureoftheobject,andthereremains We then suggest yet another alternative date for the a possibility that the whole story is a legend created SN,which deserves furtherinvestigation. to glorify theStuart King, as asign of divinefavour4. 2 The 1630 noon-star: comet 2chandra.harvard.edu/edu/formal/icecore/king charles.html 3Thisishowhedescribedhimselfonamemorialstonein or supernova? thenow-demolishedchurchofSantaMariadellaPassarella, inMilan. 4Similarstories areknown forother famous rulers. For Comets are the most obvious candidate for a “new example, on 1671 August 28, “the very night of the mar- star” unexpectedly appearing in the sky. Indeed, the riage [between Czar Peter the Great’s parents] a brilliant 1630 star was sometimes called “a comet” by contem- star was perceived quite close to the planet Mars, and www.publish.csiro.au/journals/pasa 3 In the Italian record, the memory of the event could be distorted by the popular belief that plagues were heralded by comets. Alternatively, implausible as it may seem, there could have been a bright comet and asupernovaintheskyatthesametime(CasAwould indeed be seen towards the North). To make the sit- uation even more confusing, there was also an almost totalsolareclipse5 visiblefromLondonanhourbefore sunseton1630May31JulianCalendar(June10inthe Gregorian Calendar), with a magnitude (that is, the fraction of thediameter ofthesolar diskin eclipse) of 93%, whichcouldhaveenhancedtheperceptionofas- trological significance for the alleged noon-star event reported two daysearlier. 3 Japanese records Strom (2002) cites the apparition of a bright object (star or comet) near the Sun, on 1630 August 5, reported by the Chinese Ancient Records of Celestial Phenomena (BAO1988). Strom (2002)’s favourite interpretation is a sungrazing comet belonging to the Kreutz group, seen at perihelion6. If the comet peri- helionwasinAugust,itisunlikelythatthesamecomet could bevisible in daylight already in June. For an independent test on this and other 17th- centuryevents,wedecidedtosearch foradditional in- formationintheJapanesearchives. Welookedintothe Dai-Nihon Shiryo Unified Database7, the most com- plete Japanese historical archives. Only the chrono- logical historyrecordsbetweenAD887and1622 have beencompiledandprintedbytheHistoriographicalIn- stituteoftheUniversityofTokyosofar;however,sub- sequentrecordswillbepublishedinthenextfewyears. We obtained access to yet-unpublished hand-written records covering the rest of the 17th century. We did find a “guest star” happening in the year Kan’ei 7th (corresponding to 1630). The annals’ entry for the 7th month, 8th day of the Japanese calendar, corresponding to August 16, is “fine weather, a guest star appeared in the East” (Fig. 2). We conclude that the Chinese and Japanese records reported the same object, but we do not have enough evidence to identify it with theEuropean event. We then searched for other possible events in the Dai-NihonShiryo,consistentwith aSNinCassiopeia, between 1630 and 1700. We did not find any plausible candidates. There are a few objects identified as “broom stars” (comets), or with corresponding detec- Figure 2: Excerpts from the Dai-Nihon Shiryo tions in China that are identified as comets, based on theirdescription of appearance and motion in thesky (Japanese historical annals), mentioning the ap- (seealsoadiscussiononthemeaningofbroomstarsin pearance of a guest star on 1630 August 16. Im- ageownedbytheHistoriographicalInstituteofthe was thought by the two astrologers to be a good omen” University of Tokyo; courtesy of Prof. Toru Hoya. (Sta¨hlinvonStorksburg 1788). In 1941, North Korean DearLeaderKimJong-il’sbirthwasallegedlyheraldedby a brightnew star inthe heavens and a double rainbow all thewayacrossthesky(eg.,French2007). 5eclipse.gsfc.nasa.gov/SEsearch/ SEsearchmap.php?Ecl=16300610 6CharlesII’sbirthstarismistakenlydated1648May29 inStrom(2002)’stable1andtext. 7www.hi.u-tokyo.ac.jp/english/publication/ dainihonshiryo-e.html 4 Publications of theAstronomical Society of Australia Stephenson & Green 2005a,b). For example, one seen catalogue hosted by the Harvard-Smithsonian Center in China on 1668 March 3–12, and reported in the for Astrophysics9. Sixty-eight of them have a host Dai-Nihon Shiryo entry of 1668 March 8; another one galaxy identification and a discovery or peak visual reported in the Chinese records on 1679 September 2 brightness. We converted the apparent brightness to and in theJapanese archives on 1679 August 21. absolute magnitudes, using the cosmology-corrected An interesting pair of (likely) separate events is luminosity distances in NED10, which are based on mentioned in the entry for the year Sho¯ho¯ 4th, 5th the 3K cosmic microwave background frame. We also month, 25th day, which translates as 1647 June 27 correctedeachsourceforline-of-sightextinction,using in the Gregorian calendar (a year corresponding to a the values from Schlafly & Finkbeiner (2011). When Greenland nitrate spike, McCracken et al. 2001): “a theoptical bandis not well definedor specified in the mysteriousbrightobjectflewintheNorth-Easternsky; Asiago Catalogue (as is thecase for most SNediscov- also, a guest star appeared in the West, something I ered byamateurastronomers), weusedtheextinction have never seen in my life before”. However, there is in the V band. For a few well-studied SNe (1993J: no evidenceto connect either of these two events(the Schmidt et al. 1993; 1996cb: Qiu et al. 1999; 2001ig: first of which isperhapsa brightmeteor) with Cas A. Bembrick et al. 2002; 2008ax: Pastorello et al. 2008; Abrightnewobjectreportedtohavebeenseeninthe 2011dh: Arcavi et al. 2011), we used more accurate East-NorthEastskyatdawnon1661July17couldbe peak brightnesses from individual studies in the liter- anothersun-grazingcomet. Similarly,on1671Novem- ature,ratherthanthevalueslisted intheAsiago Cat- ber29, a“hakki”(aword usuallyreferring tometeors alogue, but the difference is generally small and does orcomets)appeared“between7and9pmintheWest- not affect our general conclusions. We plot the re- ern sky, looking like a bright column of light”: but sultingabsolute brightnessdistribution inFig. 3. The that is obviously not where Cas A would have been distribution is clearly peaked at −17.5 <∼ M <∼−16.5 located. As for the year 1680 (alleged Flamsteed de- mag. Thetailofthedistributionatfaintermagnitudes tection),theonlycelestialeventintheJapaneseannals is probably dueto objects being discovered past their is, as expected, the Great Comet observed in Decem- peak brightness. The small number of sources with ber, well reported in European and North American −18.5<∼M <∼−19magmaybelongtoadifferentsub- historical records. class of Type IIb SNe, or may be mis-classifications, but that is beyond the scope of this paper. We are alsoawarethatthecataloguecontainsamixtureofdis- 4 Brightness of Type IIb SNe covery andpeak brightnesses, and often non-standard photometric bands or visual estimates; however, the A key assumption of the1630 noon-star identification mainpointofourexerciseissimplytoshowthatmost is that the Cas A SN must have been bright enough Type IIb SNe reach a characteristic absolute bright- to be seen in daylight, as was the Tycho SN in 1572. ness ∼ −17 mag. (See Richardson et al. 2006, 2002 Wenowdiscusswhetherthisisthecase. Opticalspec- for thebrightness distribution of otherclasses of SNe, troscopic studies of the light echo from Cas A have based on the Asiago Catalogue.) The distance of Cas revelead(Krause et al.2008)thatthesupernovawasof A is 3.4+0.3 kpc (Reed et al. 1995), that is a distance −0.1 TypeIIb. ThismeansthatitstartedasaTypeII(with modulus=12.7+−00..21 mag. Addinganextinction AV ∼ hydrogen lines) but quickly evolved to a Type Ib (no 8mag(Krauseet al.2008)resultsinanapparentpeak hydrogenlines). Thistypeofeventswasrecognizedas brightnessmV ∼3–4magforCasA,clearlynotvisible a distinct class only a few years ago, and its physical in day light, and not particularly impressive at night, interpretation is still disputed (Claeys et al. 2011). It either. appears that the progenitor star has only a thin layer ofhydrogenleft,withamassMH ∼0.1–0.5M⊙ whenit collapses. In one scenario (Podsiadlowski et al. 1993), 5 Additional evidence against theprogenitorstarfillsitsRochelobeinabinarysys- a 1630 Cas A identification temandtransfersmost ofitshydrogenenvelopetoits massivecompanionstar. Anotherscenario(Nomoto et al. 1993) suggests that two massive stars in abinary sys- Another constraint on the explosion date comes from temactuallymerge,formingacommonenvelope,which analysesofthepropermotionoftheejecta. Suchstud- is mostly but not entirely removed by the energy re- ies haveconsistently indicated a datelater than 1650. leased by thein-spiralling of the two cores, before the More specifically, Thorstensen et al. (2001) extrapo- implosion of the merged core. Observationally, a few lated an undecelerated convergence date of 1671.3± percentofcore-collapseSNearenowidentifiedasType 0.9,fromasampleof17brightknotsforwhicharchival IIb,with wildly discrepant estimates going from 1.5% imaging data was available overat least 50 years. Us- tomorethan10%(eg,Arcavi et al.2010;Smartt2009; ingalargersampleof72brightand/orcompactknots Smith et al. 2011; Claeys et al. 2011 for a review). imagedbytheHubbleSpaceTelescope,Fesen et al.(2006) Thereare76SNeidentifiedasTypeIIbintheAsi- estimated an explosion date of 1671.8±17.9 (again, ago Catalogue8 (Barbon et al. 1999); we also cross- neglecting deceleration). Using instead a subsample checkedtheAsiagolistwiththeListofSupernovaeweb of knotsfrom thenorthwestern limb, which appear to havesufferedtheleastamountofdeceleration,Fesen et al. 8Mostupdatedversionavailableonline: heasarc.gsfc.nasa.gov/W3Browse/star- 9cfa-www.harvard.edu/iau/lists/Supernovae.html catalog/asiagosn.html 10ned.ipac.caltech.edu www.publish.csiro.au/journals/pasa 5 0 2 e N S e IIb 15 p y T of ber 10 m u N 5 0 −14 −15 −16 −17 −18 −19 Absolute visual brightness (mag) Figure 3: Absolute visual magnitude of the 68 Type-IIb SNe identified since 1993 with a reliable host galaxy identification. Peak brightness were usedwheneverpossible;otherwise,weadopteddis- covery brightnesses from the Asiago catalogue. (2006) estimated 1680.5±18.7. Finally, we need to consider a common-sense argument. If the 1630 day-time object was real, and seen bysomany common people, it musthavecaught theattentionalsoofnaturalphilosophers,astrologers, astronomers, mathematicians, theologians. When a ”new star” (Tycho’s SN) appeared in Cassiopeia in 1572 (Brahe 1573), it sparked tremendous interest, with philosophicalandscientificdiscussionsabout the nature of fixed stars, for the first time unequivocally showingsignsofchangeratherthanbeingperfectand eternal. The new object was immediately reported in sky charts and mentioned in letters and academic treaties. A similar ”new star” event in 1630 (in the same region of sky!) would have been equally well reported,ormore,consideringtheprogressofastronomy in the intervening six decades. That was clearly not thecase;thelackofinterestisconsistentwiththe1630 event being a more familiar event (meteor or comet). Figure 4: Header and excerpts from Jean Gal- 6 The 1671 Cassini report lois’s report on new stars, published on the Jour- nal des Sçavans in 1671. We argue that the 4th- Based on thecharacteristic age extrapolated from the magnitudestarinCassiopeia(neverseenbeforeor ejecta, as discussed in Section 5, we decided to focus since) could be the Cas A SN. our search for further clues between about the years 1660and1680. Bythattime,observationalastronomy had become more advanced in Europe than in East Asia, and a 3th–4th mag object would be more likely to be discovered and catalogued there. If there was onepersonintheOldContinentspecificallyinterested in the study of variable or new stars, that was Gian DomenicoCassini(1625–1712). Cassiniandhiscollab- orator and academic successor Geminiano Montanari (1633–1687) established the first systematic survey of variable stars at the University of Bologna in the late 1660s(afterMontanarihadserendipitouslydiscovered the variability of Algol in 1667). Cassini moved to Parison1669 April4,invitedbyKingLouisXIV,but 6 Publications of theAstronomical Society of Australia continuedtopursuethislineofresearchfromthenewly established RoyalObservatory in Paris, which opened in1671. Hewasthemostrenownedandprobablymost skilled astronomer in ContinentalEurope at thetime, enjoying the same prestige as the British Astronomer Royal SirJohn Flamsteed. Only a minimal part of Cassini’s manuscript ob- servationrecordshavebeencataloguedandpublished; otherinformationonhisworkisavailablefromsecond- hand reports. We searched and found an article writ- tenbythenaturalphilosopherandmathematicianJean Gallois (1632–1707), on the “Journal des S¸cavans” (a prestigiousFrenchliteraryandscientificjournalfounded andeditedbyGalloishimself),datedMonday22June 1671 (Gallois 1671). The topic of the article is variable stars. Gallois writes (page 35): ”M. Cassini en a découvert plusieurs autres [étoiles] plus petites, de la nouveauté desquelles il y a de grandes presomptions. Par exemple, il en a observé une de la 4e grandeur & deuxdela5e dansCassiopée, ou` ilest certainqu’elles ne se voyoient pas auparavant, plusieurs Astronomes ayantexactementcomptéjusqu’auxpluspetitesEtoiles decetteconstellation,&pasund’euxn’ayantparlédé ces trois-la`”. This article is extremely important, because Gallois is very likely reporting what he heard directly from Cassini; the two scientists were close friends and Gallois used to proof-read the Frenchlan- guage of Cassini’s scientific communications (Cassini 1810). In summary, Cassini reported the discovery of a 4th-magnitude star in Cassiopeia in 1671 (together with two fainter ones), a star that was not accounted for in any previous sky chart. This is interesting because we know that all 4th- magnitude stars in Cassiopeia had already been discovered and published in sky charts decades before Cassini’s observations. For example, we examined Jo- hannBayer’sUranometria(Bayer1603)andcompared itwithtoday’sHipparcoscatalogue(van Leeuwen2007). Bayer’schartiscompletedowntoV =4.83mag. This completeness limit takes into account a couple of bi- nary stars that could not be visually resolved at the beginning of the 17th century. Notice that some of Bayer’sstars(inparticular,50Cas,V =3.95mag)are drawn with the correct location and magnitude in his chartsbutdidnotreceiveaGreek-letterclassification: that is routinely thecase for stars located outside the “classical” boundary of a constellation defined by the drawingofitstraditionalmythologicalfigure. Wealso Figure 5: Header and excerpts from the Histoire checkedthat Bayer’sscale ofvisual magnitudescorre- de l’Académie Royale des Sciences, reporting on sponds to today’s definition;we found that stars clas- Maraldi’scommunicationin1694thatsomeofthe < < sifiedas“4thmagnitude”correspondto3.5∼V ∼4.5 new stars found by Cassini in Cassiopeia were no magintheHipparcoscatalog. Therefore,thereshould longer visible. be no ambiguity when Cassini mentions thediscovery of a 4th-magnitudestar. Twenty-fiveyearsafterthepublicationofUranome- tria, Julius Schiller (1580–1627) worked with Johann Bayer (1572–1625) to create a revised and updated stellar atlas (Schiller 1627). Schiller did not simply replace all of the pagan constellations with Christian figures: he added several new stars discovered after thepublicationofBayer’scharts,andrefinedtheirpo- sitions. WeexaminedSchiller’smapofCassiopeia and foundthatitiscompletedowntoV =4.95mag(again, www.publish.csiro.au/journals/pasa 7 + Cas A SN 1572 Figure 6: An ancient star map: “St Mary Magdalen alias Cassiopeia” in Schiller’s Coelum Stellatum Christianum (circa 1627); source: the Linda Hall Library of Science, Engineering & Technology. We overplotted the positions of Cas A and of Tycho’s SN 1572. 8 Publications of theAstronomical Society of Australia 4=γ 12=β 20=υ Cas A 14=τ 30 3=η 13=ρ 2=α NGC 281 Figure 7: A modern sky map, from GoogleSky (circa 2012), showing the eastern section of Cassiopeia. We labelled some of the stars with Schiller’s numbers and Bayer’s Greek letters. Size of the image: 13◦×5◦.5. North is up, east to the left. Schiller’s star Number 30 (present but not labelled in Bayer’s map) is known today as AR Cas, and it may be the object Flamsteed really saw in 1680 (Kamper 1980; Green & Stephenson 2003). allowing for unresolved doublestars). Cassini (Cassini II)’s Elemens d’astronomie (Cassini CassiniwascertainlywellfamiliarwithbothBayer’s 1740), although he appears to summarize the infor- and Schiller’s charts. We find it impossible to believe mation previously reported by Gallois and Maraldi: thatthebestastronomer inEuropeatthetimewould ”Outre ces étoiles dont on vient de faire le rapport, not know all the dozen-or-so 4th-magnitude stars of mon pereen adécouvertplusieursautrespluspetites, Cassiopeia, orthatheestimated thewrongbrightness qu’on présume être nouvelles. Par exemple, il en a for his nouvelle étoile. That is even more implau- observé une de la quatrieme grandeur, & deux de la sible considering that Cassiopeia had probably been cinquieme, dans la constellation de Cassiopée, ou` il themost closely monitored region of theskysince the est certain qu’ellesnesevoyoientpauauparavant,n’y stunningappearanceofSN1572,andthatCassiniwas ayantaucunAstronomequienaitfaitmention,quoiqu’il specificallyinterestedinvariablestarsandthereforein y en ait eu plusieurs qui ayent exactement compté thepossibilityofare-appearanceofthatsource. More- jusqu’auxpluspetitesétoilesdecetteconstellation. En over,Cassiopeia iscircumpolarfrom Europe,soitcan 1671,iltrouvacinqnouvellesétoliesdanslaCassiopée, be observed all year round. As for the other two new dont trois avoient disparu”. stars observed by Cassini in Cassiopeia in or before We do not know the coordinates of the transient 1671, they were of 5th magnitude, at which level the 4th-magnitudestardiscoveredbyCassiniinCassiopeia, existingchartswerenotcomplete;thereforewedonot nor of the other variable ones. Cas A is outside the need to invokespecial variability for those. traditional mythological boundaries of Cassiopeia, lo- The next reference we found about Cassini’s new cated between Cassiopeia and Cepheus: this may ex- stars in Cassiopeia is from the ”Histoire & Mémoires plainwhyitslocation wasnotreportedmoreprecisely de l’Académie Royale des Sciences” (Maraldi 1694). at the time. Moreover, we should not assume (based WereadtherethattheItalian-FrenchastronomerGia- on the words used by Gallois and Maraldi) that the comoFilippo(JacquesPhilippe)Maraldi(1665–1729), firstobservationofthetransientstarinCassiopeiaoc- inductedintotheAcadémiein 1694 andresearch staff curred precisely in the first half of 1671. Cassini was memberattheParisObservatorysince1687,presented known to observe his targets meticulously for years, a report “On changes of the apparent brightness of sometimes, before reporting a result or a new discov- stars” (”Sur les changemens de grandeur apparentes ery. This caveat is important in view of the nitrate des Etoiles”). Maraldi’s communication was read to spike detected in the 1667 ice layers. On the other the Académie on 1694 December 4. Secretary Jean- hand,on1668July2,theJournaldesS¸cavansreported BaptisteDuHamel(1623–1706)summarizeditassuch, onthe“Apparizionicelestidell’anno1668osservatein in theHistoire: ”Dansl’année 1671 M. Cassini trouva Bologna da Gio. Domenico Cassini Astronomo dello 5étoilesnouvellesdansCassiopée;iln’yenaàprésent studiopublico”(Gallois1668),inwhichothervariable que deux qui subsistent, les trois autres ont disparu. stars are mentioned, butnot those in Cassiopeia. Maisilyenatroisautresnouvellesdela6e grandeur, To make further progress, we need to access and une au piedestal de la chaise, l’autre au ventre, & la search through the original records of Cassini’s ob- dernière à la poitrine”. servations, especially those between 1669 and 1671. A further mention of the variable stars in Cas- Such documents are still kept in the archives of the siopeiaobservedbyCassiniisfoundinhissonJacques Paris Observatory,andhaveneverbeen catalogued or www.publish.csiro.au/journals/pasa 9 scanned. As we send this paper to press, we are still Bayer, J. 1603, “Uranometria: omnium asterismorum negotiatingthepossibilityofaccessingthosearchivein continensschemata, novamethododelineata, aereis Parisforfurtherresearch. Hopefully,wewillreporton laminis expressa”, C. Mangus Ed., Augsburg (Ger- this in follow-up work. But for now, we can already many) propose that Cassini’s 1671 reported observation of a Beijing Astronomical Observatory [BAO] (Chief edi- 4th-magnitude transient star in Cassiopeia is at least as strong a candidate for Cas A as Flamsteed’s 1680 tor) 1988, Zhongguogudaitianxiangjiluzongji, observation. Jiangsu Science and Technology Publishing House, Nanjing Bembrick,C.,Pearce,A.,Evans,R.2002,IAUC,7804, 7 Conclusions 2 We examined recent claims that the Cas A SN might Brahe,T.1573,“Denovaetnulliusaevimemoriaprius be identified with a 1630 “noon-star” reported in the visa stella iam pridem anno a nato Christo 1572, Englishliterature. Westronglydisfavourthispossibil- mense Novembri primum conspecta, contemplatio ity,basedontheexpectedbrightnessofaType-IIbSN mathematica”, Copenhagen,LaurentiusBenedictus (toofainttobeseenindaylight),theextrapolatedmo- Brown, M. A. 2010, in ”The Pleiadic Age of Stuart tionoftheejecta(inconsistentwithanyexplosiondate Poesie: RestorationUranography,Dryden’sJudicial earlier than at least 1650), the lack of any scholarly Astrology,andtheFateofAnneKilligrew”,English reference totheevent. Wedetailstrong evidencethat Theses, Georgia StateUniversity,page49andfoot- there was a bright comet in 1630 June, but we found notes no evidence to determine whether it could be visible indaylight. Wealsofoundnorecordofday-timeguest Cassini, J. [Cassini II] 1740, in “Elemens stars or broom stars consistent with a1630 Cas A SN d’astronomie”, Paris, Imprimerie Royale, pages in the Japanese archives. Based on the motion of the 72–73 ejecta, we focused our search for the Cas A progenitor to the years between about 1660 and 1680, and Cassini IV, J.-D., 1810, in ”Mémoires pour servir à to the astronomers who would have been most likely l’Histoire des Sciences et à celle de l’Observatoire to notice it: Gian Domenico Cassini and his collab- Royal de Paris, suivis de la vie de J.-D. Cassini, orators, who were doing pioneering work on variable écrite par lui-même, et des éloges de plusieurs stars. We found a report about a 4th-magnitude star Académiciens morts pendant la Révolution”, Paris, (that is, with the brightness expected for the Cas A Bleuet, pages 292–293 SN) discovered by Cassini in Cassiopeia in or shortly before 1671 (the same epoch inferred for the event by Claeys,J.S.W.,deMink,S.E.,Pols,O.R.,Eldridge, Thorstensen et al.2001),whichwasnotseenbeforeor J. J., Baes, M. 2011, A&A,528, 131 since. We argue that this source could be the long- Dreschhoff,G.A.M.,Laird,C.M.2006,AdSpRes,38, soughtSN,butfurtherresearchintheoriginalobserv- 1307 ing logs (kept at the Paris Observatory) is needed to determine the discovery date and coordinates of the Dreschhoff,G.A.M., Zeller,E.J.1990, SolPhys,127, transient Cassiopeia object observed by Cassini. 333 Fesen, R. A.,et al. 2006, ApJ, 645, 283 Acknowledgments French, P. 2007, in “North Korea: The Paranoid Peninsula: AModernHistory”,London,ZedBooks, We thank Fabrizio Bònoli, Valeria Zanini, Suzanne p. 57 Débarbat, Nicola Masetti, Naomi Mockford and an anonymousrefereefortheirsuggestionsandcomments. Gallois, J. 1668, “Apparizioni celesti dell’anno 1668 WethankToru Hoyaand HidenoriOuchifortheir in- osservate in Bologna daGio. 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