text: serpens serpens ( " the serpent " , greek ὄφις ) is a constellation of the northern hemisphere . one of the 48 constellations listed by the 2nd - century astronomer ptolemy , it remains one of the 88 modern constellations defined by the international astronomical union . it is unique among the modern constellations in being split into two non - contiguous parts , serpens caput ( serpent head ) to the west and serpens cauda ( serpent tail ) to the east . between these two halves lies the constellation of ophiuchus , the " serpent - bearer " . in figurative representations , the body of the serpent is represented as passing behind ophiuchus between mu serpentis in serpens caput and nu serpentis in serpens cauda . the brightest star in serpens is the red giant star alpha serpentis , or , in serpens caput , with an apparent magnitude of 2 . 63 . also located in serpens caput are the naked - eye globular cluster messier 5 and the naked - eye variables r serpentis and serpentis . notable extragalactic objects include seyfert 's sextet , one of the densest galaxy clusters known ; arp 220 , the prototypical ultraluminous infrared galaxy ; and hoag 's object , the most famous of the very rare class of galaxies known as ring galaxies . part of the milky way 's galactic plane passes through serpens cauda , which is therefore rich in galactic deep - sky objects , such as the eagle nebula ( ic ) and its associated star cluster messier 16 . the nebula measures 70 light - years by 50 light - years and contains the pillars of creation , three dust clouds that became famous for the image taken by the hubble space telescope . other striking objects include the red square nebula , one of the few objects in astronomy to take on a square shape ; and 40 , a massive nearby star - forming region consisting of a molecular cloud and an h ii region . history in greek mythology , serpens represents a snake held by the healer asclepius . represented in the sky by the constellation ophiuchus , asclepius once killed a snake , but the animal was subsequently resurrected after a second snake placed a revival herb on it before its death . as snakes shed their skin every year , they were known as the symbol of rebirth in ancient greek society , and legend says asclepius would revive dead humans using the same technique he witnessed . although this is likely the logic for serpens ' presence with ophiuchus , the true reason is still not fully known . sometimes , serpens was depicted as coiling around ophiuchus , but the majority of atlases showed serpens passing either behind ophiuchus ' body or between his legs . in some ancient atlases , the constellations serpens and ophiuchus were depicted as two separate constellations , although more often they were shown as a single constellation . one notable figure to depict serpens separately was johann bayer ; thus , serpens ' stars are cataloged with separate bayer designations from those of ophiuchus . when eugène delporte established modern constellation boundaries in the 1920s , he elected to depict the two separately . however , this posed the problem of how to disentangle the two constellations , with deciding to split serpens into two areas — the head and the tail — separated by the continuous ophiuchus . these two areas became known as serpens caput and serpens cauda , caput being the latin word for head and cauda the latin word for tail . in chinese astronomy , most of the stars of serpens represented part of a wall surrounding a marketplace , known as tianshi , which was in ophiuchus and part of hercules . serpens also contains a few chinese constellations . two stars in the tail represented part of , the tower with the market office . another star in the tail represented , jewel shops . one star in the head ( mu serpentis ) marked , the crown prince 's wet nurse , or sometimes rain . there were two " serpent " constellations in babylonian astronomy , known as and . it appears that was depicted as a hybrid of a dragon , a lion and a bird , and loosely corresponded to hydra . was a horned serpent ( c.f. ) and roughly corresponds to the ὄφις constellation of eudoxus of cnidus on which the ὄφις ( serpens ) of ptolemy is based . characteristics serpens is the only one of the 88 modern constellations to be split into two disconnected regions in the sky : serpens caput ( the head ) and serpens cauda ( the tail ) . the constellation is also unusual in that it depends on another constellation for context ; specifically , it is being held by the serpent bearer ophiuchus . serpens caput is bordered by libra to the south , virgo and boötes to the east , corona borealis to the north , and ophiuchus and hercules to the west ; serpens cauda is bordered by sagittarius to the south , scutum and aquila to the east , and ophiuchus to the north and west . covering 636 . 9 square degrees total , it ranks 23rd of the 88 constellations in size . it appears prominently in both the northern and southern skies during the northern hemisphere 's summer . its main asterism consists of 11 stars , and 108 stars in total are brighter than magnitude 6 . 5 , the traditional limit for naked - eye visibility . serpens caput 's boundaries , as set by eugène delporte in 1930 , are defined by a 15 - sided polygon , while serpens cauda 's are defined by a 25 - sided polygon . in the equatorial coordinate system , the right ascension coordinates of serpens caput 's borders lie between 15h and 16h , while the declination coordinates are between 25 . 66 ° and − 03 . 72 ° . serpens cauda 's boundaries lie between right ascensions of 17h and 18h and declinations of 06 . 42 ° and − 16 . 14 ° . the international astronomical union ( iau ) adopted the three - letter abbreviation " ser " for the constellation in 1922 . notable features stars head stars marking the heart of the serpent is the constellation 's brightest star , alpha serpentis . traditionally called , is a red giant of spectral type k2iii located approximately 23 parsecs distant with a visual magnitude of 2 . 630 ± 0 . 009 , meaning it can easily be seen with the naked eye even in areas with substantial light pollution . a faint companion is in orbit around the red giant star , although it is not visible to the naked eye . situated near alpha is lambda serpentis , a magnitude 4 . 42 ± 0 . 05 star rather similar to the sun positioned only 12 parsecs away . another solar analog in serpens is the primary of psi serpentis , a binary star located slightly further away at approximately 14 parsecs . beta , gamma , and iota serpentis form a distinctive triangular shape marking the head of the snake , with kappa serpentis being roughly midway between gamma and iota . the brightest of the four with an apparent magnitude of roughly 3 . 67 , beta serpentis is a white main - sequence star roughly 160 parsecs distant . it is likely that a nearby 10th - magnitude star is physically associated with beta , although it is not certain . the mira variable r serpentis , situated between beta and gamma , is visible to the naked eye at its maximum of 5th - magnitude , but , typical of mira variables , it can fade to below magnitude 14 . gamma serpentis itself is an f - type subgiant located only 11 parsecs distant and thus is quite bright , being of magnitude 3 . 84 ± 0 . 05 . the star is known to show solar - like oscillations . delta serpentis , forming part of the body of the snake between the heart and the head , is a multiple star system positioned around 70 parsecs from earth . consisting of four stars , the system has a total apparent magnitude of 3 . 79 as viewed from earth , although two of the stars , with a combined apparent magnitude of 3 . 80 , provide nearly all the light . the primary , a white subgiant , is a delta scuti variable with an average apparent magnitude of 4 . 23 . positioned very near delta , both in the night sky and likely in actual space at an estimated distance of around 70 parsecs , is the barium star 16 serpentis . another notable variable star visible to the naked eye is chi serpentis , an alpha ² canum venaticorum variable situated midway between delta and beta which varies from its median brightness of 5 . 33 by 0 . 03 magnitudes over a period of approximately 1 . 5 days . the two stars in serpens caput that form part of the snake 's body below the heart are epsilon and mu serpentis , both third - magnitude a - type main - sequence stars . both have a peculiarity : epsilon is an am star , while mu is a binary . located slightly northwest of mu is 36 serpentis , another a - type main - sequence star . this star also has a peculiarity ; it is a binary with the primary component being a lambda boötis star , meaning that it has solar - like amounts of carbon , nitrogen , and oxygen , while containing very low amounts of iron peak elements . 25 serpentis , positioned a few degrees northeast of mu serpentis , is a spectroscopic binary consisting of a hot b - type giant and an a - type main - sequence star . the primary is a slowly pulsating b star , which causes the system to vary by 0 . 03 magnitudes . serpens caput contains many rr lyrae variables , although most are too faint to be seen without professional photography . the brightest is vy serpentis , only of 10th magnitude . this star 's period has been increasing by approximately 1 . 2 seconds per century . a variable star of a different kind is serpentis , a cool red giant that pulsates between magnitudes 5 . 89 and 7 . 07 in 87 days . this star has been found to display an inverse p cygni profile , where cold infalling gas on to the star creates redshifted hydrogen absorption lines next to the normal emission lines . several stars in serpens have been found to have planets . the brightest , omega serpentis , located between epsilon and mu , is an orange giant with a planet of approximately 1 . 7 jupiter - masses . nn serpentis , an eclipsing post - common - envelope binary consisting of a white dwarf and a red dwarf , is very likely to have two planets causing variations in the period of the eclipses . although it does not have a planet , the solar analog hd has been found to have a brown dwarf companion within the brown - dwarf desert . psr + 11 is a system consisting of two neutron stars orbiting each other , one of which is a pulsar with a period of 37 . 9 milliseconds . situated approximately 1000 parsecs distant , the system was used to test albert einstein 's theory of general relativity , validating the system 's relativistic parameters to within 0 . 2 % of values predicted by the theory . the x - ray emission from the system has been found to be present when the non - pulsar star intersects the equatorial pulsar wind of the pulsar , and the system 's orbit has been found to vary slightly . tail stars the brightest star in the tail , eta serpentis , is similar to alpha serpentis ' primary in that it is a red giant of spectral class k. this star , however , is known to exhibit solar - like oscillations over a period of approximately 2 . 16 hours . the other two stars in serpens cauda forming its asterism are theta and xi serpentis . xi , where the asterism crosses over to mu serpentis in the head , is a triple star system located approximately 105 parsecs away . two of the stars , with a combined apparent magnitude of around 3 . 5 , form a spectroscopic binary with an angular separation of only 2 . 2 milliarcseconds , and thus cannot be resolved with modern equipment . the primary is a white giant with an excess of strontium . theta , forming the tip of the tail , is also a multiple system , consisting of two a - type main - sequence stars with a combined apparent magnitude of around 4 . 1 separated by almost half an arcminute . lying near the boundary with ophiuchus are zeta , nu , and omicron serpentis . all three are 4th - magnitude main - sequence stars , with nu and omicron being of spectral type a and zeta being of spectral type f. nu is a binary star with a 9th - magnitude companion , while omicron is a delta scuti variable with amplitude variations of 0 . 01 magnitudes . in 1909 , the symbiotic nova rt serpentis appeared near omicron , although it only reached a maximum magnitude of 10 . the star system 59 serpentis , also known as d serpentis , is a triple star system consisting of a spectroscopic binary containing an a - type star and an orange giant and an orange giant secondary . the system shows irregular variations in brightness between magnitudes 5 . 17 and 5 . 2 . in 1970 , the nova fh serpentis appeared just slightly north of 59 serpentis , reaching a maximum brightness of 4 . 5 . also near 59 serpentis in the serpens cloud are several orion variables . mwc 297 is a herbig be star that in 1994 exhibited a large x - ray flare and increased in x - ray luminosity by five times before returning to the quiescent state . the star also appears to possess a circumstellar disk . another orion variable in the region is vv serpentis , a herbig ae star that has been found to exhibit delta scuti pulsations . vv serpentis has also , like mwc 297 , been found to have a dusty disk surrounding it , and is also a ux orionis star , meaning that it shows irregular variations in its brightness . the star hr , also known as mv serpentis , is an canum venaticorum variable that is faintly visible to the naked eye . the star 's metal abundance is ten times higher than the sun for most metals at the iron peak and up to 1 , 000 times more for heavier elements . it has also been found to contain excess silicon . barely visible to the naked eye is hd , a likely post - blue straggler in the open cluster ic 4756 that contains a large excess of lithium . hd , also located in ic 4756 , is an algol variable eclipsing binary with a 5 . 70 day period . the primary star in the system is also a delta scuti variable , undergoing multiple pulsation frequencies , which , combined with the eclipses , causes the system to vary by around a tenth of a magnitude . as the galactic plane passes through it , serpens cauda contains many massive ob stars . several of these are visible to the naked eye , such as nw serpentis , an early be star that has been found to be somewhat variable . the variability is interesting ; according to one study , it could be one of the first discovered hybrids between beta cephei variables and slowly pulsating b stars . although not visible to the naked eye , hd ( my serpentis ) is a beta lyrae variable triple system consisting of three very hot o - type stars . a member of the cluster ngc , the two eclipsing stars are both blue giants , with one being of the very early spectral type the remaining star is either a blue giant or supergiant of a late o or early b spectral type . also an eclipsing binary , the hd system consists of two o - type blue supergiants in orbit around each other . less extreme in terms of mass and temperature is hd , a spectroscopic binary consisting of a b - type primary and an ap secondary , although it is the only known spectroscopic binary to consist of a star with excess of mercury and manganese and an ap star . south of the eagle nebula on the border with sagittarius is the eclipsing binary w serpentis , whose primary is a white giant that is interacting with the secondary . the system has been found to contain an accretion disk , and was one of the first discovered serpentids , which are eclipsing binaries containing exceptionally strong far - ultraviolet spectral lines . it is suspected that such serpentids are in an earlier evolutionary phase , and will evolve first into double periodic variables and then classical algol variables . also near the eagle nebula is the eclipsing wolf – rayet binary cv serpentis , consisting of a wolf – rayet star and a hot o - type subgiant . the system is surrounded by a ring - shaped nebula , likely formed during the wolf – rayet phase of the primary . the eclipses of the system vary erratically , and although there are two theories as to why , neither of them is completely consistent with current understanding of stars . serpens cauda contains a few x - ray binaries . one of these , gx 17 + 2 , is a low - mass x - ray binary consisting of a neutron star and , as in all low - mass x - ray binaries , a low - mass star . the system has been classified as a - like z source , meaning that its accretion is near the eddington limit . the system has also been found to approximately every 3 days brighten by around 3 . 5 k - band magnitudes , possibly due to the presence of a synchrotron jet . another low - mass x - ray binary , serpens x - 1 , undergoes occasional x - ray bursts . one in particular lasted nearly four hours , possibly explained by the burning of carbon in " a heavy element ocean " . deep - sky objects head objects as the galactic plane does not pass through this part of serpens , a view to many galaxies beyond it is possible . however , a few structures of the milky way galaxy are present in serpens caput , such as messier 5 , a globular cluster positioned approximately 8 ° southwest of α serpentis , next to the star 5 serpentis . barely visible to the naked eye under good conditions , and is located approximately 25 , 000 ly distant . messier 5 contains a large number of known rr lyrae variable stars , and is receding from us at over 50 km / s . the cluster contains two millisecond pulsars , one of which is in a binary , allowing the proper motion of the cluster to be measured . the binary could help our understanding of neutron degenerate matter ; the current median mass , if confirmed , would exclude any " soft " equation of state for such matter . the cluster has been used to test for magnetic dipole moments in neutrinos , which could shed light on some hypothetical particles such as the . another globular cluster is palomar 5 , found just south of messier 5 . many stars are leaving this globular cluster due to the milky way 's gravity , forming a tidal tail over 30000 light - years long . a remarkable dark nebula complex is the / complex . along with a third cloud , they are likely fragments of a single original cloud located 36 degrees away from the galactic plane , a large distance for dark nebulae . the entire complex is thought to be around 140 parsecs distant . , also referred to as , is particularly interesting ; there are several infrared sources within , indicating pre - stellar sources thought to present the first known observation of the contraction phase between cloud cores and cores . the core is split into three regions , with a combined mass of around 25 solar masses . outside of the milky way , there are no bright deep - sky objects for amateur astronomers in serpens caput , with nothing else above 10th magnitude . the brightest is ngc 5962 , a spiral galaxy positioned around 28 megaparsecs distant with an apparent magnitude of 11 . 34 . slightly fainter is ngc , a barred spiral galaxy with a liner - type active galactic nucleus situated somewhat closer at a distance of 21 megaparsecs . a type ii supernova was observed in this galaxy in 2001 and was designated sn . fainter still are the spirals ngc and ngc , with the latter being host to the supernova sn . hoag 's object , located 600 million light - years from earth , is one of the most famous of a very rare class of galaxies known as ring galaxies . the outer ring is largely composed of young blue stars while the core is made up of older yellow stars . the predominant theory regarding its formation is that the progenitor galaxy was a barred spiral galaxy whose arms had velocities too great to keep the galaxy 's coherence and therefore detached . arp 220 is another unusual galaxy in serpens . the prototypical ultraluminous infrared galaxy , arp 220 is somewhat closer than hoag 's object at 250 million light - years from earth . it consists of two large spiral galaxies in the process of colliding with their nuclei orbiting at a distance of 1 , 200 light - years , causing extensive star formation throughout both components . it possesses a large cluster of more than a billion stars , partially covered by thick dust clouds near one of the galaxies ' core . another interacting galaxy pair , albeit in an earlier stage , consists of the galaxies ngc and ngc . in this case , both are active galaxies , with the former a seyfert 2 galaxy and the latter a liner - type galaxy . both are undergoing a burst of star formation triggered by the interaction . seyfert 's sextet is a group of six galaxies , four of which are interacting gravitationally and two of which simply appear to be a part of the group despite their greater distance . the gravitationally bound cluster lies at a distance of 190 million light - years from earth and is approximately 100 , 000 light - years across , making seyfert 's sextet one of the densest galaxy group known . astronomers predict that the four interacting galaxies will eventually merge to form a large elliptical galaxy . the radio source 3c 326 was originally though to emanate from a giant elliptical galaxy . however , in 1990 , it was shown that the source is instead a brighter , smaller galaxy a few arcseconds north . this object , designated 3c 326 n , has enough gas for star formation , but is being inhibited due to the energy from the radio galaxy nucleus . a much larger galaxy cluster is the redshift - 0 . abell 2063 . the cluster is thought to be interacting with the nearby galaxy group 3s , based on radial velocity measurements of galaxies and the positioning of the cd galaxy at the center of abell 2063 . the active galaxy at the center of 3s — ngc — appears to be creating a bubble of hot gas from its radio activity . near the 5th - magnitude star pi serpentis lies awm 4 , a cluster containing an excess of metals in the intracluster medium . the central galaxy , ngc , is a radio galaxy that is probably responsible for this enrichment . similar to awm 4 , the cluster abell 2052 has central cd radio galaxy , 3c 317 . this radio galaxy is believed to have restarted after a period of inactivity less than 200 years ago . the galaxy has over 40 , 000 known globular clusters , the highest known total of any galaxy as of 2002 . consisting of two quasars with a separation of less than 5 arcseconds , the quasar pair 4c 11 . 50 is one of the visually closest pairs of quasars in the sky . the two have markedly different redshifts , however , and are thus unrelated . the foreground member of the pair ( 4c 11 . 50 a ) does not have enough mass to refract light from the background component ( 4c 11 . 50 b ) enough to produce a lensed image , although it does have a true companion of its own . an even stranger galaxy pair is 3c 321 . unlike the previous pair , the two galaxies making up 3c 321 are interacting with each other and are in the process of merging . both members appear to be active galaxies ; the primary radio galaxy may be responsible for the activity in the secondary by means of the former 's jet driving material onto the latter 's supermassive black hole . a remarkable example of gravitational lensing is found in the radio galaxy 3c 324 . first thought to be a single radio galaxy with a redshift of z 1 . 206 , it was found in 1987 to actually be two galaxies , with the radio galaxy at the aforementioned redshift being lensed by another galaxy at redshift z 0 . 845 . the first example of a multiply - imaged radio galaxy discovered , the source appears to be an elliptical galaxy with a dust lane obscuring our view of the visual and ultraviolet emission from the nucleus . in even shorter wavelengths , the bl lac object pg 1553 + 113 is a heavy emitter of gamma rays . this object is the most distant found to emit photons with energies in the tev range as of 2007 . the spectrum is unique , with hard emission in some ranges of the gamma - ray spectrum in stark contrast to soft emission in others . in 2012 , the object flared in the gamma - ray spectrum , tripling in luminosity for two nights , allowing the redshift to be accurately measured as z 0 . 49 . several gamma - ray bursts ( grbs ) have been observed in serpens caput , such as grb , one of the brightest grbs observed . an optical transient event associated with this grb has not been found , despite its intensity . the host galaxy initially also proved elusive , however it now appears that the host is a seyfert i galaxy located at redshift z 0 . 657 . the x - ray afterglow of the grb has also been much fainter than for other dimmer grbs . more distant is grb ( redshift z 3 . 221 ) , from which x - ray and optical afterglows were detected . this grb was surprisingly faint for a long - duration grb . tail objects part of the galactic plane passes through the tail , and thus serpens cauda is rich in deep - sky objects within our own galaxy . the eagle nebula and its associated star cluster , messier 16 lie 7 , 000 light - years from earth in the direction of the galactic center . the nebula measures 70 light - years by 50 light - years and contains the pillars of creation , three dust clouds that became famous for the image taken by the hubble space telescope . the stars being born in the eagle nebula , added to those with an approximate age of 5 million years have an average temperature of 45 , 000 kelvins and produce prodigious amounts of radiation that will eventually destroy the dust pillars . despite its fame , the eagle nebula is fairly dim , with an integrated magnitude of approximately 6 . 0 . the star - forming regions in the nebula are often evaporating gaseous globules ; unlike bok globules they only hold one protostar . north of messier 16 , at a distance of approximately 2000 parsecs , is the ob association serpens ob2 , containing over 100 ob stars . around 5 million years old , the association appears to still contain star - forming regions , and the light from its stars is illuminating the hii region s 54 . within this hii region is the open cluster ngc , which is the same age as the surrounding ob association , and the cluster is now thought to simply be the densest part of it . the cluster appears to be producing a thermal chimney of ionized gas , caused by the interaction of the gas from the galactic disk with the galactic halo . another open cluster in serpens cauda is ic 4756 , containing at least one naked - eye star , hd ( another naked - eye star in the vicinity , hd , is most likely unrelated ) . positioned approximately 440 parsecs distant , the cluster is estimated to be around 800 million years old , quite old for an open cluster . despite the presence of the milky way in serpens cauda , one globular cluster can be found : ngc , although invisible to the naked eye , can be made out in small telescopes just north of zeta serpentis . rather small and sparse for a globular cluster , this cluster contains no known rr lyrae variables , which is unusual for a globular cluster . mwc 922 is a star surrounded by a planetary nebula . dubbed the red square nebula due to its similarities to the red rectangle nebula , the planetary nebula appears to be a nearly perfect square with a dark band around the equatorial regions . the nebula contains concentric rings , which are similar to those seen in the supernova sn 1987a . mwc 922 itself is an fs canis majoris variable , meaning that it is a be star containing exceptionally bright hydrogen emission lines as well as select forbidden lines , likely due to the presence of a close binary . east of xi serpentis is another planetary nebula , abell 41 , containing the binary star mt serpentis at its center . the nebula appears to have a bipolar structure , and the axis of symmetry of the nebula has been found to be within 5 ° of the line perpendicular to the orbital plane of the stars , strengthening the link between binary stars and bipolar planetary nebulae . on the other end of the stellar age spectrum is , a dark nebula which contains the protostar iras - . although classified as a class 0 protostar , it has some unusual features for such an object , such as a lack of high - velocity stellar winds , and it has been proposed that this object is in transition between class 0 and class i. a variable nebula exists around the protostar , although it is only visible in infrared light . the serpens cloud is a massive star - forming molecular cloud situated in the southern part of serpens cauda . only two million years old and 420 distant , the cloud is known to contain many protostars such as serpens 1 and serpens svs 20 . the serpens south was uncovered by nasa 's spitzer space telescope in the southern portion of the cloud , and it appears that star formation is still continuing in the region . another site of star formation is the 40 complex , consisting of a prominent hii region adjacent to a molecular cloud . located around 500 parsecs distant , it is one of the nearest massive regions of star formation , but as the molecular cloud obscures the hii region , rendering it and its embedded cluster tough to see visibly , it is not as well - studied as others . the embedded cluster likely contains over 600 stars above 0 . 1 solar masses , with several massive stars , including at least one o - type star , being responsible for lighting the hii region and the production of a bubble . despite the presence of the milky way , several active galaxies are visible in serpens cauda as well , such as pds 456 , found near xi serpentis . the most intrinsically luminous nearby active galaxy , this agn has been found to be extremely variable in the x - ray spectrum . this has allowed light to be shed on the nature of the supermassive black hole at the center , likely a kerr black hole . it is possible that the quasar is undergoing a transition from an ultraluminous infrared galaxy to a classical radio - quiet quasar , but there are problems with this theory , and the object appears to be an exceptional object that does not completely lie within current classification systems . nearby is 530 , a blazar that has been known to flare in the x - rays occasionally . one of these flares was for less than 2000 seconds , making it the shortest flare ever observed in a blazar as of 2004 . the blazar also appears to show periodic variability in its radio wave output over two different periods of six and ten years . meteor showers there are two daytime meteor showers that radiate from serpens , the omega serpentids and the sigma serpentids . both showers peak between december 18 and december 25 .