Serpens ( grc, , , the Serpent) is a

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...

, it remains one of the

88 modern constellations In contemporary astronomy, 88 constellations are recognized by the International Astronomical Union (IAU). Each constellation is a region of the sky, bordered by arcs of right ascension and declination. Together they cover the celestial spher ...

designated by the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

. 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 Ophiuchus () is a large constellation straddling the celestial equator. Its name comes from the Ancient Greek (), meaning "serpent-bearer", and it is commonly represented as a man grasping a snake. The serpent is represented by the constella ...

, 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 A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around o ...

star Alpha Serpentis, or Unukalhai, in Serpens Caput, with an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

of 2.63. Also located in Serpens Caput are the naked-eye

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

Messier 5 and the naked-eye variables

R Serpentis R Serpentis is a Mira variable type star in the equatorial constellation of Serpens. It ranges between apparent magnitude 5.16 and 14.4, and spectral types M5e to M8e, over a period of 356.41 days. The variability of this star was disc ...

and Tau⁴ Serpentis. Notable extragalactic objects include

Seyfert's Sextet Seyfert's Sextet is a group of galaxies about 190 million light-years away in the constellation Serpens. The group appears to contain six members, but one of the galaxies, NGC 6027d, is a background object and another "galaxy," NGC 6027e, i ...

, one of the densest galaxy clusters known;

Arp 220 Arp 220 is the result of a collision between two galaxies which are now in the process of merging. It is the 220th object in Halton Arp's ''Atlas of Peculiar Galaxies''. Features Arp 220 is the closest Ultraluminous Infrared Galaxy (ULIRG) to ...

, the prototypical ultraluminous infrared galaxy; and

Hoag's Object Hoag's Object is an unusual ring galaxy in the constellation of Serpens Caput. It is named after Arthur Hoag, who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy. The galaxy has approximately eight bill ...

, 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 object A deep-sky object (DSO) is any astronomical object that is not an individual star or Solar System object (such as Sun, Moon, planet, comet, etc.). The classification is used for the most part by amateur astronomers to denote visually observed fa ...

s, such as the Eagle Nebula (IC 4703) and its associated star cluster

Messier 16 Messier may refer to: People with the surname *Charles Messier, French astronomer *Éric Messier, former NHL defenseman *George Messier, French inventor *Jean-Marie Messier, former CEO of Vivendi Universal *Marc Messier, Canadian actor from Quebec ...

. The

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

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 Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

. Other striking objects include the

Red Square Nebula The Red Square Nebula is a celestial object located in the area of the sky occupied by star MWC 922 in the constellation Serpens. The first images of this bipolar nebula, taken using the Mt. Palomar Hale telescope in California, were released ...

, one of the few objects in astronomy to take on a square shape; and Westerhout 40, a massive nearby

star-forming region Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

consisting of a

molecular cloud A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydroge ...

and an

H II region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds ...

History

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities o ...

, Serpens represents a

snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more ...

held by the healer

Asclepius Asclepius (; grc-gre, Ἀσκληπιός ''Asklēpiós'' ; la, Aesculapius) is a hero and god of medicine in ancient Greek religion and mythology. He is the son of Apollo and Coronis, or Arsinoe, or of Apollo alone. Asclepius represen ...

. Represented in the sky by the constellation

, 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 Johann Bayer (1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain, Lower Bavaria, in 1572. At twenty, in 1592 he began his study of philosophy and law at the University of Ingolstadt, ...

; thus, Serpens' stars are cataloged with separate

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars ...

s 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 Deporte 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 Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categorized in the tw ...

, 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 Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the ...

. Serpens also contains a few

Chinese constellations Traditional Chinese astronomy has a system of dividing the celestial sphere into asterisms or constellations, known as "officials" ( Chinese ''xīng guān''). The Chinese asterisms are generally smaller than the constellations of Hellenisti ...

. Two stars in the tail represented part of Shilou, the tower with the market office. Another star in the tail represented Liesi, jewel shops. One star in the head ( Mu Serpentis) marked Tianru, the

crown prince A crown prince or hereditary prince is the heir apparent to the throne in a royal or imperial monarchy. The female form of the title is crown princess, which may refer either to an heiress apparent or, especially in earlier times, to the w ...

's wet nurse, or sometimes

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...

. There were two "serpent" constellations in

Babylonian astronomy Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia. Babylonian astronomy seemed to have focused on a select group of stars and constellations known as Ziqpu stars. These constellation ...

, known as Mušḫuššu and Bašmu. It appears that Mušḫuššu was depicted as a hybrid of a dragon, a lion and a bird, and loosely corresponded to Hydra. Bašmu was a horned serpent (c.f. Ningishzida) and roughly corresponds to the Ὄφις constellation of

Eudoxus of Cnidus Eudoxus of Cnidus (; grc, Εὔδοξος ὁ Κνίδιος, ''Eúdoxos ho Knídios''; ) was an ancient Greek astronomer, mathematician, scholar, and student of Archytas and Plato. All of his original works are lost, though some fragments are ...

on which the Ὄφις (''Serpens'') of Ptolemy is based.

Characteristics

Serpens is the only one of the

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 Virgo may refer to: *Virgo (astrology), the sixth astrological sign of the zodiac * Virgo (constellation), a constellation *Virgo Cluster, a cluster of galaxies in the constellation Virgo *Virgo Stellar Stream, remains of a dwarf galaxy * Virgo Su ...

and

Boötes Boötes ( ) is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from la, Boōtēs, which comes from grc-gre, Βοώτης, Boṓtē ...

to the west, Corona Borealis to the north, and Ophiuchus and

to the east; Serpens Cauda is bordered by Sagittarius to the south,

Scutum The ''scutum'' (; plural ''scuta'') was a type of shield used among Italic peoples in antiquity, most notably by the army of ancient Rome starting about the fourth century BC. The Romans adopted it when they switched from the military formatio ...

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 Belgian astronomer Eugène Delporte in 1930, are defined by a 10-sided polygon, while Serpens Cauda's are defined by a 22-sided polygon. In the

equatorial coordinate system The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth, a fu ...

, the

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the ( hour circle of the) point in question above the earth. When pair ...

coordinates of Serpens Caput's borders lie between and , while the

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of th ...

coordinates are between and . Serpens Cauda's boundaries lie between right ascensions of and and declinations of and . The

(IAU) adopted the three-letter abbreviation "Ser" for the constellation in 1922.

Features

Stars

Head stars

Marking the heart of the serpent is the constellation's brightest star, Alpha Serpentis. Traditionally called Unukalhai, is a

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

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. It has an exoplanet orbiting around it. Another

solar analog Solar-type star, solar analogs (also analogues), and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type ...

in Serpens is the primary of Psi Serpentis, a binary star located slightly further away at approximately 14 parsecs.

Beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...

Gamma Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter r ...

, and Iota Serpentis form a distinctive triangular shape marking the head of the snake, with Kappa Serpentis (the proper name is Gudja) 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

, 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 A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

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. Iota Serpentis is a binary star system. 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 Barium stars are spectral class G to K stars whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4 nm. Barium stars also show enhanced spectral features of carbon, the ...

16 Serpentis. Another notable variable star visible to the naked eye is Chi Serpentis, an Alpha² 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. Chi Serpentis is a chemically peculiar star. The two stars in Serpens Caput that form part of the Snake's body below the heart are

Epsilon Epsilon (, ; uppercase , lowercase or lunate ; el, έψιλον) is the fifth letter of the Greek alphabet, corresponding phonetically to a mid front unrounded vowel or . In the system of Greek numerals it also has the value five. It was d ...

and Mu Serpentis, both third-magnitude

A-type main-sequence star An A-type main-sequence star (A V) or A dwarf star is a main-sequence ( hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure betwe ...

s. Both have a peculiarity: Epsilon is an

Am star An Am star or metallic-line star is a type of chemically peculiar star of spectral type A whose spectrum has strong and often variable absorption lines of metals such as zinc, strontium, zirconium, and barium, and deficiencies of others, such as ca ...

, 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 Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

, and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

, while containing very low amounts of iron peak elements. The secondary star has also been a source of X-ray emissions. 25 Serpentis, positioned a few degrees northeast of Mu Serpentis, is a

spectroscopic binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in w ...

consisting of a hot B-type giant and an A-type main-sequence star. The primary is a

slowly pulsating B star A slowly pulsating B-type star (SPB), formerly known as a 53 Persei variable, is a type of pulsating variable star. They may also be termed a long-period pulsating B star (LPB). As the name implies, they are main-sequence stars of spectral type B2 ...

, which causes the system to vary by 0.03 magnitudes. Serpens Caput contains many

RR Lyrae variable RR Lyrae variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype a ...

s, 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 Tau⁴ 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

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in fr ...

ed hydrogen absorption lines next to the normal emission lines. Several stars in Serpens have been found to have

planets A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a youn ...

. The brightest, Omega Serpentis, located between Epsilon and Mu, is an orange giant with a planet of at least 1.7

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...

-masses.

NN Serpentis NN Serpentis (abbreviated NN Ser) is an eclipsing post-common envelope binary system approximately 1670 light-years away. The system comprises an eclipsing white dwarf and red dwarf. The two stars orbit each other every 0.13 days. Plan ...

, an eclipsing post-common-envelope binary consisting of a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...

and a

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. ...

, 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 137510 has been found to have a

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

companion within the brown-dwarf desert. PSR B1534+11 is a system consisting of two

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...

s orbiting each other, one of which is a

pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

with a period of 37.9 milliseconds. Situated approximately 1000 parsecs distant, the system was used to test

Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theor ...

's theory of

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...

, validating the system's relativistic parameters to within 0.2% of values predicted by the theory. The

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

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 Eta Serpentis, Latinized from η Serpentis, is a star in the constellation Serpens. In particular, it lies in Serpens Cauda, the snake's tail. The star has an apparent visual magnitude of 3.260, making it visible to the naked eye. Paral ...

, 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 Theta (, ; uppercase: Θ or ; lowercase: θ or ; grc, ''thē̂ta'' ; Modern: ''thī́ta'' ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals, it has a value of 9. G ...

and

Xi Serpentis Xi Serpentis, Latinized from ξ Serpentis, is a triple star system in the Serpens Cauda (tail) section of the equatorial constellation Serpens. Based upon an annual parallax shift of 30.98 mas as seen from Earth, it is located 105 ...

. 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 Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in par ...

of only 2.2 milli

arcseconds A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The ...

, and thus cannot be resolved with modern equipment. The primary is a

white giant A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

with an excess of

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is e ...

. 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. There is also a third G-type star with a mass and radius similar to that of the Sun. See Table 3. Lying near the boundary with Ophiuchus are

Zeta Zeta (, ; uppercase Ζ, lowercase ζ; grc, ζῆτα, el, ζήτα, label= Demotic Greek, classical or ''zē̂ta''; ''zíta'') is the sixth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 7. It was derived f ...

, 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 single star with a 9th-magnitude visual companion, while Omicron is a Delta Scuti variable with amplitude variations of 0.01 magnitudes. In 1909, the

symbiotic nova Symbiotic novae are slow irregular eruptive variable stars with very slow nova-like outbursts with an amplitude of between 9 and 11 magnitudes. The symbiotic nova remains at maximum for one or a few decades, and then declines towards its original ...

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 FH Serpentis (Nova Serpentis 1970) was a nova, which appeared in the constellation Serpens in 1970. It reached magnitude 4.4. It was discovered on February 13, 1970 by Minoru Honda located at Kurashiki, Japan. Other astronomers later stu ...

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

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 A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are th ...

. 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 6958, also known as MV Serpentis, is an Alpha² 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 Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

. Barely visible to the naked eye is HD 172365, a likely post- blue straggler in the open cluster IC 4756 that contains a large excess of

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense soli ...

. HD 172189, also located in IC 4756, is an

Algol variable Algol variables or Algol-type binaries are a class of eclipsing binary stars that are similar to the prototype member of this class, β Persei (Beta Persei, Algol). An Algol binary is a system where both stars are near-spherical such that ...

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 Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

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 variable Beta Cephei variables, also known as Beta Canis Majoris stars, are variable stars that exhibit small rapid variations in their brightness due to pulsations of the stars' surfaces, thought due to the unusual properties of iron at temperatures of 200 ...

s and slowly pulsating B stars. Although not visible to the naked eye, HD 167971 (MY Serpentis) is a Beta Lyrae variable triple system consisting of three very hot

O-type star An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvin (K). Stars of this type have strong absorption lines of ionised helium, ...

s. A member of the cluster NGC 6604, the two eclipsing stars are both blue giants, with one being of the very early spectral type O7.5III. The remaining star is either a blue giant or

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars spa ...

of a late O or early B spectral type. Also an eclipsing binary, the HD 166734 system consists of two O-type blue supergiants in orbit around each other. Less extreme in terms of mass and temperature is HD 161701, 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 Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...

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 An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other ...

, 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

, 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 X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively normal star), to the other component, called the ''accretor'', which ...

. One of these, GX 17+2, is a

low-mass X-ray binary X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively normal star), to the other component, called the ''accretor'', which ...

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 Sco-like Z source, meaning that its accretion is near the

Eddington limit The Eddington luminosity, also referred to as the Eddington limit, is the maximum luminosity a body (such as a star) can achieve when there is balance between the force of radiation acting outward and the gravitational force acting inward. The stat ...

. 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". Φ 332 (Finsen 332) is a tiny and difficult double-double star at 18:45 / +5°30', named Tweedledee and Tweedledum by South African astronomer William Stephen Finsen, who was struck by the nearly identical position angles and separations at the time of his 1953 discovery. Gliese 710 is a star that is expected to pass very close to the Solar System in around 1.29 million years.

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

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 Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distan ...

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 In physics, chemistry, and thermodynamics, an equation of state is a thermodynamic equation relating state variables, which describe the state of matter under a given set of physical conditions, such as pressure, volume, temperature, or intern ...

for such matter. The cluster has been used to test for

magnetic dipole moment In electromagnetism, the magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagnet ...

s in neutrinos, which could shed light on some hypothetical particles such as the

axion An axion () is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest ...

. The brightest stars in Messier 5 are around magnitude 10.6, and the globular cluster was first observed by

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...

in 1791. 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 A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the ...

over 30000 light-years long. It is over 11 billion years old. It has also been flattened and distorted by tidal effects. The L134/ L183 is a

dark nebula A dark nebula or absorption nebula is a type of interstellar cloud, particularly molecular clouds, that is so dense that it obscures the visible wavelengths of light from objects behind it, such as background stars and emission or reflection neb ...

complex that, along with a third cloud, is likely formed by 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. L183, also referred to as L134N, is home to several infrared sources, indicating pre-stellar sources thought to present the first known observation of the contraction phase between cloud cores and prestellar 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 Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae'' with an apparent magnitude of 11.34. Two supernovae have been observed in the galaxy, and NGC 5962 has two satellite galaxies. Slightly fainter is NGC 5921, a

barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxies ...

with a

LINER A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O+, N+, and S+. ...

-type

active galactic nucleus An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not prod ...

situated somewhat closer at a distance of 21 megaparsecs. A

type II supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...

was observed in this galaxy in 2001 and was designated SN 2001X. Fainter still are the spirals NGC 5964 and NGC 6118, with the latter being host to the

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...

SN 2004dk.

, located 600 million light-years from Earth, is a member of the 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.

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 Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

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 5953 and NGC 5954. In this case, both are

active galaxies An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not pro ...

, with the former a

Seyfert 2 galaxy Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra ...

and the latter a LINER-type galaxy. Both are undergoing a burst of star formation triggered by the interaction.

is a

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

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 may refer to: Science and technology Astronomy * Cluster (spacecraft), constellation of four European Space Agency spacecraft * Asteroid cluster, a small asteroid family * Cluster II (spacecraft), a European Space Agency mission to study th ...

lies at a distance of 190 million

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88 ...

s 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 An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Real ...

. 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-0.0354 Abell 2063. The cluster is thought to be interacting with the nearby galaxy group MKW 3s, based on radial velocity measurements of galaxies and the positioning of the

cD galaxy The type-cD galaxy (also cD-type galaxy, cD galaxy) is a galaxy morphology classification, a subtype of type-D galaxy, type-D Elliptical galaxy#Sizes and shapes, giant elliptical galaxy. Characterized by a large galactic halo, halo of stars, they ...

at the center of Abell 2063. The active galaxy at the center of MKW 3s— NGC 5920—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 6051, is a

radio galaxy A radio galaxy is a galaxy with giant regions of radio emission extending well beyond its visible structure. These energetic radio lobes are powered by jets from its active galactic nucleus. They have luminosities up to 1039 W at radio wav ...

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. Galaxy3C321-composite

Consisting of two quasars with a separation of less than 5

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...

s, 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 supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical ob ...

. An example of

gravitational lens A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known ...

ing is found in the radio galaxy

3C 324 3C may refer to: In astronomy: * 3C, the '' Third Cambridge Catalogue of Radio Sources'', an astronomical reference series In business: * Long March 3C, a 2008 Chinese orbital rocket * 3C Records, a record label * 3C (radio), a defunct digital r ...

. First thought to be a single overluminous 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 A BL Lacertae object or BL Lac object is a type of active galactic nucleus (AGN) or a galaxy with such an AGN, named after its prototype, BL Lacertae. In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and ...

PG 1553+113 is a heavy emitter of

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

s. This object is the most distant found to emit photons with energies in the

TeV TEV may refer to: * Transient Earth Voltage: a term for voltages appearing on the metal work of switchgear due to internal partial discharges * TeV, or teraelectronvolt or trillion electron volt, a measure of energy * Total Enterprise Value, a ...

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 burst In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten millise ...

s (GRBs) have been observed in Serpens Caput, such as GRB 970111, 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 060526 (redshift ''z'' = 3.221), from which X-ray and optical afterglows were detected. This GRB was very 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,

lie around 5,700 light-years from Earth in the direction of the galactic center. The

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

. 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

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and ...

s 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 A protostar is a very young star that is still gathering mass from its parent molecular cloud. The protostellar phase is the earliest one in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 50 ...

. North of Messier 16, at a distance of approximately 2000 parsecs, is the

OB association In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...

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 An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds ...

S 54. Within this HII region is the open cluster NGC 6604, 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 A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of galaxies comprise the halo: * the stellar halo * the galactic corona (hot gas, i.e. a plas ...

. Another open cluster in Serpens Cauda is IC 4756, containing at least one naked-eye star, HD 172365 (another naked-eye star in the vicinity, HD 171586, 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 6535, 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 A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelate ...

. Dubbed the

due to its similarities to the

Red Rectangle Nebula The Red Rectangle Nebula, so called because of its red color and unique rectangular shape, is a protoplanetary nebula in the Monoceros constellation. Also known as HD 44179, the nebula was discovered in 1973 during a rocket flight associated w ...

, 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 SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately from Earth and was the closest observed supernova since Kepler's Supernova. 1987A's light reached Earth on ...

. MWC 922 itself is an

FS Canis Majoris variable An FS Canis Majoris variable (FS CMa star) is a type of eruptive variable star. The class of variable stars are named after its prototype, FS Canis Majoris. They are somewhat poorly understood, but are probably binary star systems in which mass exc ...

, meaning that it is a Be star containing exceptionally bright

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identi ...

s as well as select

forbidden line In spectroscopy, a forbidden mechanism (forbidden transition or forbidden line) is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particu ...

s, 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 L483, a dark nebula which contains the protostar IRAS 18418-0440. Although classified as a class 0 protostar, it has some unusual features for such an object, such as a lack of high-velocity

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. ...

s, 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. W40 (=Sh2-64)

The Serpens cloud is a massive star-forming

situated in the southern part of Serpens Cauda. Only two million years old and 420 parsecs distant, the cloud is known to contain many protostars such as Serpens FIRS 1 and Serpens SVS 20. The Serpens South protocluster was uncovered by NASA's

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, ...

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 Westerhout 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 Bubble, Bubbles or The Bubble may refer to: Common uses * Bubble (physics), a globule of one substance in another, usually gas in a liquid ** Soap bubble * Economic bubble, a situation where asset prices are much higher than underlying fund ...

. 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 The Kerr metric or Kerr geometry describes the geometry of empty spacetime around a rotating uncharged axially symmetric black hole with a quasispherical event horizon. The Kerr metric is an exact solution of the Einstein field equations of gen ...

. 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 NRAO 530, a

blazar A blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet composed of ionized matter traveling at nearly the speed of light) directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from t ...

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 Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...

output over two different periods of six and ten years.

Meteor showers

There are two daytime

meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extr ...

s that radiate from Serpens, the Omega Serpentids and the Sigma Serpentids. Both showers peak between December 18 and December 25.

References

External links

The Deep Photographic Guide to the Constellations: Serpens (Caput)

*
Warburg Institute Iconographic Database (medieval and early modern images of Serpens)
more can be found unde
Serpentarius
{{DEFAULTSORT:Serpens Constellations Equatorial constellations Constellations listed by Ptolemy Legendary serpents