SerpensFrom Wikipedia, the free encyclopediaSerpensConstellationSerpens CaputSerpens CaudaList of stars in SerpensAbbreviationSerGenitiveSerpentisPronunciation /srpnz/,genitive /srpnts/Symbolismthe SnakeRight ascension Serpens Caput: 15h 10.4m to 16h 22.5mSerpens Cauda: 17h 16.9m to 18h 58.3mDeclinationSerpens Caput: 25.66 to 03.72Serpens Cauda: 06.42 to 16.14Family HerculesAreaSerpens Caput: 428 sq. deg.Serpens Cauda: 208 sq. deg.Total: 637 sq. deg. (23rd)Main stars11Bayer/Flamsteedstars 57Stars with planets15Stars brighter than 3.00m1Stars within 10.00 pc (32.62 ly)2Brightest star Ser (Unuk lh i) (2.63m)Ne rest st rGJ 1224(24.60 ly, 7.54 pc)Messier objects 2Borderingconstell tions Serpens C put:Coron Bore lisBotesVirgoLibrOphiuchusHerculesSerpens C ud :AquilOphiuchusS gitt riusScutumVisible t l titudes between +80 nd 80.Best visible t 21:00 (9 p.m.) during the month of July.Serpens ("the Serpent", Greek ) s a constellaton o the northern hemsphere. One o the 48 constellatons lsted by the 2nd-century astronomer Ptolemy, t remansone o the 88 modern constellatons dened by the Internatonal Astronomcal Unon. It s unque among the modern constellatons n beng splt nto two non-contguous parts, Serpens Caput (Serpent's Head) to the west and Serpens Cauda (Serpent's Tal) to the east. Between these two halves les the constellaton o Ophuchus, the "Serpent-Bearer". In guratve representatons, the body o the serpent s represented as passng behnd Ophuchus between Mu Serpents n Serpens Caput and Nu Serpents n Serpens Cauda.The brghtest star n Serpens s the red gant star Alpha Serpents, or Unukalha, n Serpens Caput, wth an apparent magntude o 2.63. Also located n SerpensCaput are the naked-eye globular cluster Messer 5 and the naked-eye varablesR Serpents and Tau4 Serpents. Notable extragalactc objects nclude Seyert'sSextet, one o the densest galaxy clusters known; Arp 220, the prototypcal ultr

alumnous nrared galaxy; and Hoag's Object, the most amous o the very rare class o galaxes known as rng galaxes.Part o the Mlky Way's galactc plane passes through Serpens Cauda, whch s thereore rch n galactc deep-sky objects, such as the Eagle Nebula (IC 4703) and ts assocated star cluster Messer 16. The nebula measures 70 lght-years by50 lght-years and contans the Pllars o Creaton, three dust clouds that became amous or the mage taken by the Hubble Space Telescope. Other strkng objects nclude the Red Square Nebula, one o the ew objects n astronomy to take on a square shape; and Westerhout 40, a massve nearby star-ormng regon consstng o a molecular cloud and an H II regon.Contents [hde]1 Hstory2 Characterstcs3 Notable eatures3.1 Stars3.1.1 Head stars3.1.2 Tal stars3.2 Deep-sky objects3.2.1 Head objects3.2.2 Tal objects3.3 Meteor showers4 Reerences5 External lnksHstory[edt]Serpens shown as a snake beng held by Ophuchus n Urana's Mrror.Serpens held by Ophuchus, as depcted n Urana's Mrror, a set o constellaton cards publshed n London c. 1825. Above the tal o the serpent s the now-obsolete constellaton Taurus Ponatov whle below t s ScutumIn Greek mythology, Serpens represents a snake held by the healer Asclepus. Represented n the sky by the constellaton Ophuchus, Asclepus once klled a snake, but the anmal was subsequently resurrected ater a second snake placed a revval herb on t beore ts death. As snakes shed ther skn every year, they were known as the symbol o rebrth n ancent Greek socety, and legend says Asclepus would revve dead humans usng the same technque he wtnessed. Although ths s lkely the logc or Serpens' presence wth Ophuchus, the true reason sstll not ully known. Sometmes, Serpens was depcted as colng around Ophuchus, but the majorty o atlases showed Serpens passng ether behnd Ophuchus'body or between hs legs.[1]In some ancent atlases, the constellatons Serpens and Ophuchus were depctedas two separate constellatons, although more oten they were shown as a sngleconstellaton. One notable gure to depct Serpens separately was Johann Bayer;thus, Serpens' stars are cataloged wth separate Bayer desgnatons rom thoseo Ophuchus. When Eugne Delporte establshed modern constellaton boundares nthe 1920s, he elected to depct the two separately. However, ths posed the problem o how to dsentangle the two constellatons, wth Deporte decdng to spltSerpens nto two areasthe head and the talseparated by the contnuous Ophuchus.These two areas became known as Serpens Caput and Serpens Cauda,[1] caput bengthe Latn word or head and cauda the Latn word or tal.[2]In Chnese astronomy, most o the stars o Serpens represented part o a wall surroundng a marketplace, known as Tansh, whch was n Ophuchus and part o Hercules. Serpens also contans a ew Chnese constellatons. Two stars n the tal represented part o Shlou, the tower wth the market oce. Another star nthe tal represented Les, jewel shops. One star n the head (Mu Serpents) marked Tanru, the crown prnce's wet nurse, or sometmes ran.[1]There were two "serpent" constellatons n Babylonan astronomy, known as Muuu and B

amu. It appears that Muuu was depcted as a hybrd o a dragon, a lon and a brd, and loosely corresponded to Hydra. Bamu was a horned serpent (c.. Nngshzda) androughly corresponds to the constellaton o Eudoxus o Cndus on whch the (Serpeno Ptolemy s based.[3]Characterstcs[edt]Serpens s the only one o the 88 modern constellatons to be splt nto two dsconnected regons n the sky: Serpens Caput (the head) and Serpens Cauda (the tal). The constellaton s also unusual n that t depends on another constellaton or context; speccally, t s beng held by the Serpent Bearer Ophuchus.[1]Serpens Caput s bordered by Lbra to the south, rgo and Botes to the east, Corona Boreals to the north, and Ophuchus and Hercules to the west; Serpens Caudas bordered by Sagttarus to the south, Scutum and Aqula to the east, and Ophuchus to the north and west. Coverng 636.9 square degrees total, t ranks 23rdo the 88 constellatons n sze. It appears promnently n both the northern and southern skes durng the Northern Hemsphere's summer.[4] Its man astersmconssts o 11 stars, and 108 stars n total are brghter than magntude 6.5, the tradtonal lmt or naked-eye vsblty.[4]Serpens Caput's boundares, as set by Eugne Delporte n 1930, are dened by a 15-sded polygon, whle Serpens Cauda's are dened by a 25-sded polygon. In theequatoral coordnate system, the rght ascenson coordnates o Serpens Caput'sborders le between 15h 10.4m and 16h 22.5m, whle the declnaton coordnatesare between 25.66 and 03.72. Serpens C ud 's bound ries lie between right scensions of 17h 16.9m nd 18h 58.3m nd declin tions of 06.42 nd 16.14.[5] The Intern tion l Astronomic l Union (IAU) dopted the threeletter bbrevi tion "Ser" for theconstell tion in 1922.[5][6]Not ble fe tures[edit]St rs[edit]See lso: List of st rs in SerpensHe d st rs[edit]The p ttern of st rs in Serpens C put seen with the n ked eye, withtri ngle mrking the he d ndline of st rs extending down m rking the upper bodyThe constell tion Serpens (C put) s it c n be seen by the n ked eyeM rking the he rt of the serpent is the constell tion's brightest st r, Alph Serpentis. Tr dition lly c lled Unuk lh i, is red gi nt of spectr l type K2III loc ted pproxim tely 23 p rsecs dist nt with visu l m gnitude of 2.630 0.009,[7] me ning it c n e sily be seen with the n ked eye even in re s with subst ntil light pollution. A f int comp nion is in orbit round the red gi nt st r,[8]lthough it is not visible to the n ked eye. Situ ted ne r Alph is L mbd Serpentis, m gnitude 4.42 0.05 st r r ther simil r to the Sun[9] positioned only 12p rsecs w y.[10] Another sol r n log in Serpens is the prim ry of Psi Serpentis, bin ry st r[11] loc ted slightly further w y t pproxim tely 14 p rsecs.[12]Bet , G mm , nd Iot Serpentis form distinctive tri ngul r sh pe m rking thehe d of the sn ke, with K pp Serpentis being roughly midw y between G mm nd Iot . The brightest of the four with n pp rent m gnitude of roughly 3.67, BetSerpentis is white m insequence st r roughly 160 p rsecs dist nt.[13] It is likely th t ne rby 10thm gnitude st r[14] is physic lly ssoci ted with Bet ,lthough it is not cert in.[15] The Mir v ri ble R Serpentis, situ ted betweenBet nd G mm , is visible to the n ked eye t its m ximum of 5thm gnitude, but, typic l of Mir v ri bles, it c n f de to below m gnitude 14.[16] G mm Serpentis itself is n Ftype subgi nt loc ted only 11 p rsecs dist nt nd thus is quite bright, being of m gnitude 3.84 0.05.[17] The st r is known to show sol rlike oscill tions.[18]

Delt Serpentis, forming p rt of the body of the sn ke between the he rt nd thehe d, is multiple st r system[19] positioned round 70 p rsecs from E rth. Consisting of four st rs, the system h s tot l pp rent m gnitude of 3.79 s viewed from E rth,[20] lthough two of the st rs, withcombined pp rent m gnitude of 3.80, provide ne rly ll the light.[21] The prim ry, white subgi nt, isDelt Scuti v ri ble with n ver ge pp rent m gnitude of 4.23.[22] Positionedvery ne r Delt , both in the night sky nd likely in ctu l sp ce t n estim ted dist nce of round 70 p rsecs,[23] is the b rium st r 16 Serpentis.[24] Another not ble v ri ble st r visible to the n ked eye is Chi Serpentis, n Alph C num Ven ticorum v ri ble situ ted midw y between Delt nd Bet which v ries fromits medi n brightness of 5.33 by 0.03 m gnitudes over period of pproxim tely1.5 d ys.[25]The two st rs in Serpens C put th t form p rt of the Sn ke's body below the he rt re Epsilon nd Mu Serpentis, both thirdm gnitude Atype m insequence st rs.[26][27] Both h ve peculi rity: Epsilon is n Am st r,[28] while Mu isbin ry.[29] Loc ted slightly northwest of Mu is 36 Serpentis, nother Atype m insequence st r. This st r lso h s peculi rity; it is bin ry with the prim ry component being L mbd Botis st r, me ning th t it h s sol rlike mounts of c rbon, nitrogen, nd oxygen, while cont ining very low mounts of iron pe k elements.[30] 25 Serpentis, positioned few degrees northe st of Mu Serpentis, is spectroscopic bin ry[31] consisting of hot Btype gi nt nd n Atype m insequence st r. The prim ry is slowly puls ting B st r, which c uses the system to vry by 0.03 m gnitudes.[32]Serpens C put cont ins m ny RR Lyr e v ri bles, lthough most re too f int to be seen without profession l photogr phy. The brightest is VY Serpentis, only of10th m gnitude. Interestingly, this st r's period h s been incre sing by pproxim tely 1.2 seconds per century.[33] A v ri ble st r ofdifferent kind is T u4Serpentis, cool red gi nt th t puls tes between m gnitudes 5.89 nd 7.07 in 87d ys.[34] This st r h s been found to displ y n inverse P Cygni profile,[35] where cold inf lling g s on to the st r cre tes redshifted hydrogen bsorption lines next to the norm l emission lines.[36]Sever l st rs in Serpens h ve been found to h ve pl nets. The brightest, Omeg Serpentis, loc ted between Epsilon nd Mu, is n or nge gi nt with pl net of pproxim tely 1.7 Jupiterm sses.[37] NN Serpentis, n eclipsing postcommonenvelope bin ry consisting of white dw rf ndred dw rf,[38] is very likely to hve two pl nets c using v ri tions in the period of the eclipses.[39] Although itdoes not h ve pl net, the sol r n log HD 137510 h s been found to h ve brown dw rf comp nion within the browndw rf desert.[40]PSR B1534+11 is system consisting of two neutron st rs orbiting e ch other, one of which is puls r with period of 37.9 milliseconds. Situ ted pproxim tely 1000 p rsecs dist nt, the system w s used to test Albert Einstein's theory ofgener l rel tivity, v lid ting the system's rel tivistic p r meters to within 0.2% of v lues predicted by the theory.[41] The Xr y emission from the system h sbeen found to be present when the nonpuls r st r intersects the equ tori l puls r wind of the puls r, nd the system's orbit h s been found to v ry slightly.[42]T il st rs[edit]The p ttern of st rs in Serpens C ud seen with the n ked eye, with line of strs m rking the t ilThe constell tion Serpens (C ud ) s it c n be seen by the n ked eyeThe brightest st r in the t il, Et Serpentis, is simil r to Alph Serpentis' prim ry in th t it is red gi nt of spectr l cl ss K. This st r, however, is known to exhibit sol rlike oscill tions overperiod of pproxim tely 2.16 hours.[43] The other two st rs in Serpens C ud forming its sterism re Thet nd Xi Serpentis. Xi, where the sterism crosses over to Mu Serpentis in the he d, is

triple st r system[8] loc ted pproxim tely 105 p rsecs w y.[44] Two of the strs, withcombined pp rent m gnitude of round 3.5, form spectroscopic bin ry with n ngul r sep r tion of only 2.2 milli rcseconds,[45] nd thus c nnot beresolved with modern equipment. The prim ry is white gi nt with n excess ofstrontium.[44] Thet , forming the tip of the t il, is lso multiple system, consisting of two Atype m insequence st rs withcombined pp rent m gnitude ofround 4.1 sep r ted by lmost h lf n rcminute.[8]Lying ne r the bound ry with Ophiuchus re Zet , Nu, nd Omicron Serpentis. Allthree re 4thm gnitude m insequence st rs, with Nu nd Omicron being of spectrl type A[46][47] nd Zet being of spectr l type F.[48] Nu is bin ry st r[8]with 9thm gnitude comp nion,[49] while Omicron isDelt Scuti v ri ble withmplitude v ri tions of 0.01 m gnitudes.[50] In 1909, the symbiotic nov [51] RTSerpentis ppe red ne r Omicron, lthough it only re chedm ximum m gnitude of 10.[52]The st r system 59 Serpentis, lso known s d Serpentis, is triple st r system[53] consisting of spectroscopic bin ry cont ining n Atype st r nd n or nge gi nt[54] nd n or nge gi nt second ry.[55] The system shows irregul r v ritions in brightness between m gnitudes 5.17 nd 5.2.[56] In 1970, the nov FH Serpentis ppe red just slightly north of 59 Serpentis, re ching m ximum brightness of 4.5.[57] Also ne r 59 Serpentis in the Serpens Cloud re sever l Orion vri bles. MWC 297 is Herbig Be st r th t in 1994 exhibitedl rge Xr y fl rend incre sed in Xr y luminosity by five times before returning to the quiescent st te.[58] The st r lso ppe rs to possess circumstell r disk.[59] AnotherOrion v ri ble in the region is VV Serpentis, Herbig Ae st r th t h s been found to exhibit Delt Scuti puls tions.[60] VV Serpentis h s lso, like MWC 297, been found to h vedusty disk surrounding it,[61] nd is lso UX Orionis st r,[62] me ning th t it shows irregul r v ri tions in its brightness.[63]The st r HR 6958, lso known s MV Serpentis, is n Alph 2 C num Ven ticorum v ri ble th t is f intly visible to the n ked eye.[64] The st r's met l bund nce is ten times higher th n the Sun for most met ls t the iron pe k nd up to 1,000times more for he vier elements. It h s lso been found to cont in excess silicon.[65] B rely visible to the n ked eye is HD 172365,[66] likely postblue strggler in the open cluster IC 4756 th t cont ins l rge excess of lithium.[67]HD 172189, lso loc ted in IC 4756, is n Algol v ri ble eclipsing bin ry[68] with 5.70 d y period. The prim ry st r in the system is lso Delt Scuti v rible, undergoing multiple puls tion frequencies, which, combined with the eclipses, c uses the system to v ry by round tenth ofm gnitude.[69]As the g l ctic pl ne p sses through it, Serpens C ud cont ins m ny m ssive OBst rs. Sever l of these re visible to the n ked eye, such s NW Serpentis, n erly Be st r th t h s been found to be somewh t v ri ble. The v ri bility is interesting; ccording to one study, it could be one of the first discovered hybrids between Bet Cephei v ri bles nd slowly puls ting B st rs.[70] Although not visible to the n ked eye, HD 167971 (MY Serpentis) is Bet Lyr e v ri ble triple system consisting of three very hot Otype st rs. A member of the cluster NGC6604,[71] the two eclipsing st rs re both blue gi nts, with one being of the very e rly spectr l type O7.5III. The rem ining st r is either blue gi nt or supergi nt of l te O or e rly B spectr l type.[68] Also n eclipsing[72] bin ry,the HD 166734 system consists of two Otype blue supergi nts in orbit round e ch other.[73] Less extreme in terms of m ss nd temper ture is HD 161701, spectroscopic bin ry consisting ofBtype prim ry nd n Ap second ry, lthough itis the only known spectroscopic bin ry to consist of st r with excess of mercury nd m ng nese nd n Ap st r.[74]South of the E gle Nebul on the border with S gitt rius is the eclipsing bin ryW Serpentis, whose prim ry is white gi nt th t is inter cting with the secondry. The system h s been found to cont in n ccretion disk, nd w s one of the

first discovered Serpentids, which re eclipsing bin ries cont ining exception lly strong f rultr violet spectr l lines.[75] It is suspected th t such Serpentids re in n e rlier evolution ry ph se, nd will evolve first into double periodic v ri bles nd then cl ssic l Algol v ri bles.[76] Also ne r the E gle Nebulis the eclipsing WolfRayet bnary C Serpents, consstng o a WolRayet star and a hot O-type subgant. The system s surrounded by a rng-shaped nebula, lkely ormed durng the WolRayet phase o the prmary.[77] The eclpses o the system vary erratcally, and although there are two theores as to why, nether o them s completely consstent wth current understandng o stars.[78]Serpens Cauda contans a ew X-ray bnares. One o these, GX 17+2, s a low-mass X-ray bnary consstng o a neutron star and, as n all low-mass X-ray bnares, a low-mass star. The system has been classed as a Sco-lke Z source, meanng that ts accreton s near the Eddngton lmt.[79] The system has also beenound to approxmately every 3 days brghten by around 3.5 K-band magntudes, possbly due to the presence o a synchrotron jet.[80] Another low-mass X-ray bnary, Serpens X-1, undergoes occasonal X-ray bursts. One n partcular lasted nearly our hours, possbly explaned by the burnng o carbon n "a heavy elementocean".[81]Deep-sky objects[edt]Head objects[edt]Messer 5's central dense core o stars, contanng a large number o stars packed nto a small areaMesser 5, a globular cluster that can be seen wth the naked eye under good condtonsAs the galactc plane does not pass through ths part o Serpens, a vew to manygalaxes beyond t s possble. However, a ew structures o the Mlky Way Galaxy are present n Serpens Caput, such as Messer 5, a globular cluster postoned approxmately 8 southwest o Serpentis, next to the st r 5 Serpentis. B rely visible to the n ked eye under good conditions,[82] nd is loc ted pproxim tely 25,000 ly dist nt.[83] Messier 5 cont ins l rge number of known RR Lyr e v ri ble st rs,[84] nd is receding from us t over 50 km/s.[85] The cluster cont instwo millisecond puls rs, one of which is inbin ry, llowing the proper motionof the cluster to be me sured. The bin ry could help our underst nding of neutron degener te m tter; the current medi n m ss, if confirmed, would exclude ny "soft" equ tion of st te for such m tter.[86] The cluster h s been used to test for m gnetic dipole moments in neutrinos, which could shed light on some hypothetic l p rticles such s the xion.[87] Another globul r cluster is P lom r 5, found just south of Messier 5. Interestingly, m ny st rs re le ving this globul rcluster due to the Milky W y's gr vity, forming tid l t il over 30000 lightyers long.[88]A rem rk ble d rk nebul complex is the L134/L183 complex. Along withthird cloud, they re likely fr gments of single origin l cloud loc ted 36 degrees wy from the g l ctic pl ne, l rge dist nce for d rk nebul e.[89] The entire complex is thought to be round 140 p rsecs dist nt.[90] L183, lso referred to sL134N, is p rticul rly interesting; there re sever l infr red sources within, indic ting prestell r sources[91] thought to present the first known observ tionof the contr ction ph se between cloud cores nd prestell r cores.[92] The coreis split into three regions,[93] with combined m ss of round 25 sol r m sses.[94]Outside of the Milky W y, there re no bright deepsky objects for m teur stronomers in Serpens C put, with nothing else bove 10th m gnitude. The brightest is NGC 5962, spir l g l xy positioned round 28 meg p rsecs dist nt[95] with npp rent m gnitude of 11.34.[96] Slightly f inter is NGC 5921,b rred spir lg l xy with LINERtype ctive g l ctic nucleus situ ted somewh t closer t dist nce of 21 meg p rsecs.[97] A type II supernov w s observed in this g l xy in 2001 nd w s design ted SN 2001X.[98] F inter still re the spir ls NGC 5964[9

9] nd NGC 6118, with the l tter being host to the supernov

SN 2004dk.[100]

The yellow nucleus of Ho g's Object surrounded byblue ring of st rsHo g's Object, g l xy in Serpens ndmember of the very r re cl ss known sring g l xiesHo g's Object, loc ted 600 million lightye rs from E rth, is one of the most fmous of very r re cl ss of g l xies known s ring g l xies. The outer ring isl rgely composed of young blue st rs while the core is m de up of older yellow st rs. The predomin nt theory reg rding its form tion is th t the progenitor g lxy w s b rred spir l g l xy whose rms h d velocities too gre t to keep the gl xy's coherence nd therefore det ched.[101] Arp 220 is nother unusu l g l xyin Serpens. The prototypic l ultr luminous infr red g l xy, Arp 220 is somewh tcloser th n Ho g's Object t 250 million lightye rs from E rth. It consists oftwo l rge spir l g l xies in the process of colliding with their nuclei orbitingt dist nce of 1,200 lightye rs, c using extensive st r form tion throughoutboth components. It possessesl rge cluster of more th n billion st rs, p rti lly covered by thick dust clouds ne r one of the g l xies' core.[101] Anotherinter cting g l xy p ir, lbeit in n e rlier st ge, consists of the g l xies NGC 5953 nd NGC 5954. In this c se, both re ctive g l xies, with the formerSeyfert 2 g l xy nd the l tterLINERtype g l xy. Both re undergoing burstof st r form tion triggered by the inter ction.[102]Seyfert's Sextet is group of six g l xies, four of which re inter cting gr vit tion lly nd two of which simply ppe r to be p rt of the group despite their gre ter dist nce. The gr vit tion lly bound cluster lies t dist nce of 190million lightye rs from E rth nd is pproxim tely 100,000 lightye rs cross,m king Seyfert's Sextet one of the densest g l xy group known. Astronomers predict th t the four inter cting g l xies will eventu lly merge to form l rge elliptic l g l xy.[101] The r dio source 3C 326 w s origin lly though to em n te from gi nt elliptic l g l xy. However, in 1990, it w s shown th t the source is inste d brighter, sm ller g l xy few rcseconds north.[103] This object, design ted 3C 326 N, h s enough g s for st r form tion, but is being inhibited due to the energy from the r dio g l xy nucleus.[104]A much l rger g l xy cluster is the redshift0.0354 Abell 2063.[105] The clusteris thought to be inter cting with the ne rby g l xy group MKW 3s, b sed on r dil velocity me surements of g l xies nd the positioning of the cD g l xy t thecenter of Abell 2063.[106] The ctive g l xy t the center of MKW 3sNGC 5920 ppers to be cre tingbubble of hot g s from its r dio ctivity.[107] Ne r the 5thm gnitude st r Pi Serpentis lies AWM 4, cluster cont ining n excess of met ls in the intr cluster medium. The centr l g l xy, NGC 6051, isr dio g l xy tht is prob bly responsible for this enrichment.[108] Simil r to AWM 4, the cluster Abell 2052 h s centr l cD r dio g l xy, 3C 317. Interestingly, this r dio g lxy is believed to h ve rest rted fterperiod of in ctivity less th n 200 yers go.[109] The g l xy h s over 40,000 known globul r clusters, the highest known tot l of ny g l xy s of 2002.[110]A brilli nt red g l xy on the left inter cts withblue g l xy on the right, forming the merging ctive g l xy p ir 3C 321A composite im ge of 3C 321, merging ctive g l xy p irConsisting of two qu s rs with sep r tion of less th n 5 rcseconds, the qu sr p ir 4C 11.50 is one of the visu lly closest p irs of qu s rs in the sky. Thetwo h ve m rkedly different redshifts, however, nd re thus unrel ted.[111] Theforeground member of the p ir (4C 11.50 A) does not h ve enough m ss to refr ctlight from the b ckground component (4C 11.50 B) enough to produce lensed imge, lthough it does h ve true comp nion of its own.[112] An even str nger g lxy p ir is 3C 321. Unlike the previous p ir, the two g l xies m king up 3C 321re inter cting with e ch other nd re in the process of merging. Interestingly, both members ppe r to be ctive g l xies; the prim ry r dio g l xy m y be responsible for the ctivity in the second ry by me ns of the former's jet driving

m teri l onto the l tter's superm ssive bl ck hole.[113]A rem rk ble ex mple of gr vit tion l lensing is found in the r dio g l xy 3C 324. First thought to besingle overluminous r dio g l xy with redshift of z =1.206, it w s found in 1987 to ctu lly be two g l xies, with the r dio g l xyt the forementioned redshift being lensed by nother g l xy t redshift z = 0.845. The first ex mple of multiplyim ged r dio g l xy discovered,[114] the source ppe rs to be n elliptic l g l xy with dust l ne obscuring our view of the visu l nd ultr violet emission from the nucleus.[115] In even shorter w velengths, the BL L c object PG 1553+113 is he vy emitter of g mm r ys. This object is the most dist nt found to emit photons with energies in the TeV r nge s of 2007.[116] The spectrum is unique, with h rd emission in some r nges of the gmm r y spectrum in st rk contr st to soft emission in others.[117] In 2012, theobject fl red in the g mm r y spectrum, tripling in luminosity for two nights,llowing the redshift to be ccur tely me sured s z = 0.49.[118]Sever l g mm r y bursts (GRBs) h ve been observed in Serpens C put, such s GRB970111, one of the brightest GRBs observed. Interestingly, n optic l tr nsientevent ssoci ted with this GRB h s not been found, despite its intensity. The host g l xy initi lly lso proved elusive, however it now ppe rs th t the host is Seyfert I g l xy loc ted t redshift z = 0.657.[119] The Xr y fterglow ofthe GRB h s lso been much f inter th n for other dimmer GRBs.[120] More dist ntis GRB 060526 (redshift z = 3.221), from which Xr y nd optic l fterglows were detected. This GRB w s surprisingly f int for longdur tion GRB.[121]T il objects[edit]Three pill rs of op que g s st nd t ll in green nebulous b ckgroundThe Pill rs of Cre tion, wellknown st rforming region in the E gle Nebul mde f mous by this Hubble photogr phP rt of the g l ctic pl ne p sses through the t il, nd thus Serpens C ud is rich in deepsky objects within our own g l xy. The E gle Nebulnd its ssoci ted st r cluster, Messier 16 lie 7,000 lightye rs from E rth in the direction ofthe g l ctic center. The nebul me sures 70 lightye rs by 50 lightye rs nd cont ins the Pill rs of Cre tion, three dust clouds th t bec me f mous for the imge t ken by the Hubble Sp ce Telescope. The st rs being born in the E gle Nebul, dded to those with n pproxim te ge of 5 million ye rs h ve n ver ge temper ture of 45,000 kelvins nd produce prodigious mounts of r di tion th t willeventu lly destroy the dust pill rs.[101] Despite its f me, the E gle Nebul isf irly dim, with n integr ted m gnitude of pproxim tely 6.0. The st rformingregions in the nebul re often ev por ting g seous globules; unlike Bok globules they only hold one protost r.[122]North of Messier 16, t dist nce of pproxim tely 2000 p rsecs, is the OB ssoci tion Serpens OB2, cont ining over 100 OB st rs. Around 5 million ye rs old, the ssoci tion ppe rs to still cont in st rforming regions, nd the light fromits st rs is illumin ting the HII region S 54.[123] Within this HII region is the open cluster NGC 6604, which is the s me ge s the surrounding OB ssoci tion,[124] nd the cluster is now thought to simply be the densest p rt of it.[125]Interestingly, the cluster ppe rs to be producing therm l chimney of ionizedg s, c used by the inter ction of the g s from the g l ctic disk with the g l ctic h lo.[123]Another open cluster in Serpens C ud is IC 4756, cont ining t le st one n kedeye st r, HD 172365[126] ( nother n kedeye st r in the vicinity, HD 171586, ismost likely unrel ted). Positioned pproxim tely 440 p rsecs dist nt,[127] the cluster is estim ted to be round 800 million ye rs old, quite old for n open cluster.[128] Despite the presence of the Milky W y in Serpens C ud , one globul rcluster c n be found: NGC 6535, lthough invisible to the n ked eye, c n be m de out in sm ll telescopes just north of Zet Serpentis. R ther sm ll nd sp rsefor globul r cluster,[129] this cluster cont ins no known RR Lyr e v ri bles,

which is unusu l for

globul r cluster.[130]

A brilli nt red squ resh ped pl net ry nebulThe Red Squ re Nebul , one of the very few ne rperfect squ res in stronomyMWC 922 is st r surrounded by pl net ry nebul . Dubbed the Red Squ re Nebuldue to its simil rities to the Red Rect ngle Nebul , the pl net ry nebul ppers to bene rly perfect squ re with d rk b nd round the equ tori l regions.The nebul cont ins concentric rings, which re simil r to those seen in the supernov SN 1987A.[131] MWC 922 itself is n FS C nis M joris v ri ble,[132] me ning th t it is Be st r cont ining exception lly bright hydrogen emission liness well s select forbidden lines, likely due to the presence of close bin ry.[133] E st of Xi Serpentis is nother pl net ry nebul , Abell 41, cont ining the bin ry st r MT Serpentis t its center. The nebul ppe rs to h vebipol r structure, nd the xis of symmetry of the nebul h s been found to be within 5 ofthe line perpendicul r to the orbit l pl ne of the st rs, strengthening the link between bin ry st rs nd bipol r pl net ry nebul e.[134] On the other end of the stell r ge spectrum is L483,d rk nebul which cont ins the protost r IRAS184180440. Although cl ssified s cl ss 0 protost r, it h s some unusu l fetures for such n object, such s l ck of highvelocity stell r winds, nd ith s been proposed th t this object is in tr nsition between cl ss 0 nd cl ss I.[135] A v ri ble nebul exists round the protost r, lthough it is only visiblein infr red light.[136]Bright blue st rs in l rge gold cloud of g sWesterhout 40, one of the ne rest sites of m ssive st r form tionThe Serpens cloud is m ssive st rforming molecul r cloud situ ted in the southern p rt of Serpens C ud . Only two million ye rs old[137] nd 420 p recs distnt,[138] the cloud is known to cont in m ny protost rs such s Serpens FIRS 1[139] nd Serpens SVS 20.[140] The Serpens South protocluster w s uncovered by NASA's Spitzer Sp ce Telescope in the southern portion of the cloud,[141] nd it ppe rs th t st r form tion is still continuing in the region.[142] Another site ofst r form tion is the Westerhout 40 complex, consisting of prominent HII region dj cent to molecul r cloud.[143] Loc ted round 500 p rsecs dist nt,[144]it is one of the ne rest m ssive regions of st r form tion, but s the molecul rcloud obscures the HII region, rendering it nd its embedded cluster tough to see visibly, it is not s wellstudied s others.[145] The embedded cluster likely cont ins over 600 st rs bove 0.1 sol r m sses,[146] with sever l m ssive st rs, including t le st one Otype st r, being responsible for lighting the HII region nd the production of bubble.[144]Despite the presence of the Milky W y, sever l ctive g l xies re visible in Serpens C ud s well, such s PDS 456, found ne r Xi Serpentis. The most intrinsic lly luminous ne rby ctive g l xy,[147] this AGN h s been found to be extremely v ri ble in the Xr y spectrum. This h s llowed light to be shed on the n ture of the superm ssive bl ck hole t the center, likely Kerr bl ck hole.[148] It is possible th t the qu s r is undergoing tr nsition from n ultr luminous infr red g l xy to cl ssic l r dioquiet qu s r, but there re problems with this theory, nd the object ppe rs to be n exception l object th t does not completely lie within current cl ssific tion systems.[147] Ne rby is NRAO 530, blz r th t h s been known to fl re in the Xr ys occ sion lly. One of these fl resw s for less th n 2000 seconds, m king it the shortest fl re ever observed inbl z r s of 2004.[149] The bl z r lso ppe rs to show periodic v ri bility inits r dio w ve output over two different periods of six nd ten ye rs.[150]Meteor showers[edit]There re two d ytime meteor showers th t r di te from Serpens, the Omeg Serpentids nd the Sigm Serpentids. Both showers pe k between December 18 nd December 25.[151]