Serpens () is a

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

in the

northern celestial hemisphere The northern celestial hemisphere, also called the Northern Sky, is the Northern Hemisphere, northern half of the celestial sphere; that is, it lies north of the celestial equator. This arbitrary sphere diurnal motion, appears to rotate westward ...

. One of the 48 constellations listed by the 2nd-century astronomer

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

, 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 covering the entire celestial sph ...

designated by the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

. 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 Mu Serpentis, Latinized from μ Serpentis, is a binary star in the Serpens Caput (head) section of the equatorial constellation Serpens. It is visible to the naked eye with an apparent visual magnitude of 3.543. Based upon an annual par ...

in ''Serpens Caput'' and

Nu Serpentis ν Serpentis, Latinized as Nu Serpentis, is a solitary star in the Serpens Cauda section of the equatorial constellation of Serpens. It is a white-hued star that is faintly visible to the naked eye with an apparent visual magnitude of 4 ...

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 stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

star

Alpha Serpentis Alpha Serpentis or α Serpentis, formally named Unukalhai (), is a star in the head (Serpens Caput) of the equatorial constellation of Serpens. With an apparent visual magnitude of 2.6, this star is the brightest in the constellation and ...

, or Unukalhai, in Serpens Caput, with an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

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

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

Messier 5 Messier 5 or M5 (also designated NGC 5904) is a globular cluster in the constellation Serpens. It was discovered by Gottfried Kirch in 1702. Discovery and visibility M5 is, under extremely good conditions, just visible to the naked eye as a fai ...

and the naked-eye

variables Variable may refer to: Computer science * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed Mathematics * Variable (mathematics), a symbol that represents a quantity in a mathemat ...

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 discov ...

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 (700 million light years behind the g ...

, 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) ...

, the prototypical

ultraluminous infrared galaxy Luminous infrared galaxies or LIRGs are galaxies with luminosities, the measurement of brightness, above . They are also referred to as submillimeter galaxies (SMGs) through their normal method of detection. LIRGs are more abundant than starburst ...

; and Hoag's Object, the most famous of the very rare class of galaxies known as

ring galaxies A ring galaxy is a galaxy with a circle-like appearance. Hoag's Object, discovered by Arthur Hoag in 1950, is an example of a ring galaxy. The ring contains many massive, relatively young blue stars, which are extremely bright. The central region ...

. Part of the Milky Way's

galactic plane The galactic plane is the plane (geometry), plane on which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms ''galactic plane'' and ''galac ...

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 The Eagle Nebula (catalogued as Messier 16 or M16, and as NGC 6611, and also known as the Star Queen Nebula) is a young open cluster of stars in the constellation Serpens, discovered by Jean-Philippe de Cheseaux in 1745–46. Both the "Eagle" a ...

(IC 4703) and its associated star cluster

Messier 16 Messier may refer to: People with the surname *Ashley Messier (born 2002), Canadian ice hockey player *Charles Messier (1730–1817), French astronomer * Doug Messier (born 1936), Canadian ice hockey player and coach *Éric Messier (born 1973), Can ...

. The

nebula A nebula (; 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 regions, such as in the Pillars of Creation in ...

measures 70 light-years by 50 light-years and contains the

Pillars of Creation ''Pillars of Creation'' is a photograph taken by the Hubble Space Telescope that depicts elephant trunks of interstellar gas and dust in the Eagle Nebula of the Serpens constellation, some from Earth. These elephant trunks had been disco ...

, three dust clouds that became famous for the image taken by the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

. 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 Palomar Observatory Hale Telescope in California, were rele ...

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

Westerhout 40 Westerhout 40 or W40 (also designated Sharpless 64, Sh2-64, or RCW 174) is a star-forming region in the Milky Way located in the constellation Serpens. In this region, interstellar gas forming a diffuse nebula surrounds a cluster of several hund ...

, a massive nearby

star-forming region Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"— collapse and form stars. As a branch of astronomy, star formation inclu ...

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 of which the density and size permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, ...

and an

H II region An H II 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 of light year ...

History

Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...

, Serpens represents a

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

held by the healer

Asclepius Asclepius (; ''Asklēpiós'' ; ) is a hero and god of medicine in ancient Religion in ancient Greece, Greek religion and Greek mythology, mythology. He is the son of Apollo and Coronis (lover of Apollo), Coronis, or Arsinoe (Greek myth), Ars ...

. 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 Johann Bayer (; 1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain in 1572. In 1592, aged 20, he began his study of philosophy and law at the University of Ingolstadt, after which he ...

; 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 alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

s from those of Ophiuchus. When

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 China, ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categori ...

, 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 Gr ...

. 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 (

) 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, crown princess, is held by a woman who is heir apparent or is married to the heir apparent. ''Crown prince ...

's wet nurse, or sometimes

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

. There were two "serpent" constellations in

Babylonian astronomy Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia. The numeral system used, sexagesimal, was based on 60, as opposed to ten in the modern decimal system. This system simplified the ca ...

, 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 The Horned Serpent appears in the mythologies of many cultures including Native American peoples, European, and Near Eastern mythology. Details vary among cultures, with many of the stories associating the mystical figure with water, rain, li ...

(cf.

Ningishzida Ningishzida ( Sumerian: DNIN.G̃IŠ.ZID.DA, possible meaning "Lord f theGood Tree") was a Mesopotamian deity of vegetation, the underworld and sometimes war. He was commonly associated with snakes. Like Dumuzi, he was believed to spend a part ...

) and roughly corresponds to the Ὄφις constellation of

Eudoxus of Cnidus Eudoxus of Cnidus (; , ''Eúdoxos ho Knídios''; ) was an Ancient Greece, ancient Greek Ancient Greek astronomy, astronomer, Greek mathematics, mathematician, doctor, and lawmaker. He was a student of Archytas and Plato. All of his original work ...

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 Libra generally refers to: * Libra (constellation), a constellation * Libra (astrology), an astrological sign based on the star constellation Libra may also refer to: Arts and entertainment * ''Libra'' (novel), a 1988 novel by Don DeLillo Musi ...

to the south,

Virgo Virgo may refer to: Arts and entertainment * Virgo (film), a 1970 Egyptian film * Virgo (character), several Marvel Comics characters * Virgo Asmita, a character in the manga ''Saint Seiya: The Lost Canvas'' * ''Virgo'' (album), by Virgo Four, ...

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 , which comes from 'herder, herdsman' or 'plowman' (literally, 'o ...

to the west,

Corona Borealis Corona Borealis is a small constellation in the Northern Celestial Hemisphere. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and remains one of the 88 modern constellations. Its brightest stars form a sem ...

to the north, and Ophiuchus and

to the east; Serpens Cauda is bordered by

Sagittarius Sagittarius ( ) may refer to: *Sagittarius (constellation) *Sagittarius (astrology), a sign of the Zodiac * Sagittarius of Gap, a 6th century bishop *Sagittarius A*, the supermassive black hole at the center of the Milky Way galaxy Ships *'' S ...

to the south, Scutum and

Aquila Aquila may refer to: Arts, entertainment, and media * ''Aquila'', a series of books by S.P. Somtow * ''Aquila'', a 1997 book by Andrew Norriss * ''Aquila'' (children's magazine), a UK-based children's magazine * ''Aquila'' (journal), an orni ...

to the east, and Ophiuchus to the north and west. Covering 636.9

square degree __NOTOC__ A square degree (deg2) is a non- SI unit measure of solid angle. Other denotations include ''sq. deg.'' and (°)2. Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere. Analogous ...

s 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 Eugene is a common male given name that comes from the Greek εὐγενής (''eugenēs''), "noble", literally "well-born", from εὖ (''eu''), "well" and γένος (''genos''), "race, stock, kin".equatorial coordinate system The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of astronomical object, celestial objects. It may be implemented in spherical coordinate system, spherical or Cartesian coordinate system, rect ...

, 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 equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

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. The declination angle is measured north (positive) or ...

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,

. 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 Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

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 Lambda Serpentis, Latinized from λ Serpentis, is a star in the constellation Serpens, in its head (Serpens Caput). It has an apparent visual magnitude of 4.43, making it visible to the naked eye. Based upon parallax measurements, this s ...

, 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 stars, 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 ; or ) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Ancient Greek, beta represented the voiced bilabial plosive . In Modern Greek, it represe ...

Gamma Gamma (; uppercase , lowercase ; ) 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 normally repr ...

, and

Iota Serpentis ι Serpentis, Latinized as Iota Serpentis and abbreviated Iot Ser, is a triple star system in the constellation Serpens, in its head (Serpens Caput). It is approximately 190 light years from Earth. At the centre of the system is a spec ...

form a distinctive triangular shape marking the head of the snake, with

Kappa Serpentis Kappa Serpentis, Latinised from κ Serpentis, is a single, red-hued star in the constellation Serpens, in its head (Serpens Caput). It has the proper name Gudja and the Flamsteed designation 35 Serpentis. This star is visible to the ...

(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 Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wave ...

, 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 Solar-like oscillations are oscillations in star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many ot ...

. Iota Serpentis is a binary star system.

Delta Serpentis Delta Serpentis, Latinized from δ Serpentis, is a hierarchical triple star system in the constellation Serpens, in its head (Serpens Caput). The light from the two stars in the system give a combined apparent magnitude of +3.80, which ...

, 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 A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a class of pulsating star, comprising several sub-classes of object with A- or F-type spectra. The variables follow a period-luminosity ...

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 b ...

16 Serpentis 16 Serpentis is a binary star system in the Serpens Caput portion of the equatorial constellation of Serpens, located 228 light years from the Sun. It is visible to the naked eye as a fain, orange-hued star with an apparent visual ma ...

. Another notable variable star visible to the naked eye is Chi Serpentis, an

Alpha² Canum Venaticorum variable Alpha2 Canum Venaticorum variable (or α2 CVn variable) is a type of magnetic variable star. These are chemically peculiar stars of the CP2 type that are photometrically variable. That is, they are upper main sequence stars of spectral class B8p ...

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 ; ) 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 derived from the Phoenic ...

and Mu Serpentis, both third-magnitude

A-type main-sequence star An A-type main-sequence star (A) or A dwarf star is a main-sequence (hydrogen burning) star of spectral type A and luminosity class (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

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 Zinc is a chemical element; it has symbol Zn and atomic number 30. ...

, while Mu is a binary. Located slightly northwest of Mu is

36 Serpentis 36 Serpentis is a triple star system in the equatorial constellation of Serpens. It has the Bayer designation b Serpentis, while ''36 Serpentis'' is the Flamsteed designation. The system is visible to the naked eye as a dim, white-hue ...

, 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 Lambda (; uppercase , lowercase ; , ''lám(b)da'') is the eleventh letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoeni ...

, meaning that it has solar-like amounts of

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

, and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

, while containing very low amounts of

iron peak The iron peak is a local maximum in the vicinity of Iron, Fe (Chromium, Cr, Manganese, Mn, Fe, Cobalt, Co and Nickel, Ni) on the graph of the abundances of the chemical elements. For elements lighter than iron on the periodic table, nuclear fusio ...

elements. The secondary star has also been a source of X-ray emissions.

25 Serpentis 25 Serpentis is a star system in the constellation of Serpens Caput. With an apparent magnitude of 5.37, it is just barely visible to the naked eye. The system is estimated to be some 450 light-years (138 parsecs) based on its parallax. ...

, positioned a few degrees northeast of Mu Serpentis, is a

spectroscopic binary A binary star or binary star system 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 as separate stars us ...

consisting of a hot

B-type giant In astronomy, a blue giant is a hot star with a luminosity class of III (giant) or II (bright giant). In the standard Hertzsprung–Russell diagram, these stars lie above and to the right of the main sequence. The term applies to a variety of s ...

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, main-sequence stars of B- ...

, 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 P Cygni (34 Cygni) is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in ''Uranometria'' as a nova. Located about 5,300 light-years (1,560 parsecs) from Earth, it is a hypergiant ...

, 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 increase in frequency and e ...

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 generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the te ...

. The brightest,

Omega Serpentis Omega Serpentis (ω Ser, ω Serpentis) is a solitary star within the Serpens Caput part of the equatorial constellation of Serpens. It is visible to the naked eye with an apparent visual magnitude of +5.22. Based upon an annual stellar para ...

, located between Epsilon and Mu, is an

orange giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspr ...

with a planet of at least 1.7

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

-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. Plane ...

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

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

and a

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

, 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 HD may refer to: Business * H-D or Harley-Davidson, a motorcycle manufacturer * The Home Depot, NYSE stock symbol: HD Chemistry * Hydrogen deuteride, a diatomic compound of hydrogen and deuterium * Mustard gas Codes * Air Do, formerly Ho ...

has been found to have a

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

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

neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...

s orbiting each other, one of which is a

pulsar A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...

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

Albert Einstein Albert Einstein (14 March 187918 April 1955) was a German-born theoretical physicist who is best known for developing the theory of relativity. Einstein also made important contributions to quantum mechanics. His mass–energy equivalence f ...

's theory of

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

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

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

emission from the system has been found to be present when the non-pulsar star intersects the equatorial

pulsar wind A pulsar wind nebula (PWN, plural PWNe), sometimes called a plerion (derived from the Greek "πλήρης", ''pleres'', meaning "full"), is a type of nebula sometimes found inside the shell of a supernova remnant (SNR), powered by winds generate ...

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. Parall ...

, 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 ; ''thē̂ta'' ; Modern: ''thī́ta'' ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth 𐤈. In the system of Greek numerals, it has a value of 9. Gree ...

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 or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...

of only 2.2 milli

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

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

white giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspr ...

with an excess of

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

. 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; , , 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 from the Phoenician alphabet, Phoenician letter zay ...

, Nu, and

Omicron Serpentis Omicron Serpentis (ο Ser, ο Serpentis) is a solitary star in the Serpens Cauda (tail) section of the equatorial constellation Serpens. Based upon an annual parallax shift of 18.83 mas as seen from Earth, it is located around 173&nb ...

. 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 59 Serpentis, also known as d Serpentis, is a multiple star in the constellation Serpens. The system shows irregular variations in brightness between magnitudes 5.17 and 5.29. Components 59 Serpentis appears as a close pair of stars, ...

, 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 stud ...

appeared just slightly north of 59 Serpentis, reaching a maximum brightness of 4.5. Also near 59 Serpentis in the

Serpens Cloud Serpens () is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International Astronomical Union. It ...

are several

Orion variable An Orion variable is a variable star which exhibits irregular and eruptive variations in its luminosity and is typically associated with diffuse nebulae. It is thought that these are young stars which will later become regular, non-variable stars ...

s. 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 the res ...

. Another Orion variable in the region is

VV Serpentis VV, V V, or v. v. may refer to: Arts and entertainment * Vopli Vidopliassova, a Ukrainian rock band * V/V, a secondary chord in music * V.V., a character in ''Code Geass'' * Ville Valo, Finnish vocalist for gothic rock band HIM also known as VV ...

, 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 UX Orionis is a variable star in the constellation of Orion. It is a Herbig Ae star, located about 1000 light years from the Earth. At its brightest it is a magnitude 9.5 object, so it is too faint to be seen with the naked eye. UX Orion ...

, 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; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

. Barely visible to the naked eye is HD 172365, a likely post-

blue straggler A blue straggler is a type of star that is more luminous and bluer than expected. Typically identified in a stellar cluster, they have a higher effective temperature than the main sequence turnoff point for the cluster, where ordinary stars b ...

in the open cluster

IC 4756 IC 4756 is a large bright open cluster in the constellation Serpens. Known as Graff's Cluster, it is bright enough to be seen with the naked eye and considered a fine cluster for binoculars or small telescopes. IC 4756 is also known as the Tweed ...

that contains a large excess of

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

HD 172189 HD may refer to: Business * H-D or Harley-Davidson, a motorcycle manufacturer * The Home Depot, NYSE stock symbol: HD Chemistry * Hydrogen deuteride, a diatomic compound of hydrogen and deuterium * Mustard gas Codes * Air Do, formerly Ho ...

, 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

passes through it, Serpens Cauda contains many massive

OB star OB stars are hot, massive stars of spectral types O or early-type B that form in loosely organized groups called OB associations. They are short lived, and thus do not move very far from where they formed within their life. During their life ...

s. Several of these are visible to the naked eye, such as

NW Serpentis NW may refer to: Arts and entertainment * ''NW'' (novel), by Zadie Smith * Nat Wolff, a singer and actor * New wave music, a genre * '' New Weekly'', an Australian celebrity magazine * Nintendo Wii, a video game console * Northern Whig, Irish ne ...

, 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 ...

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 HD may refer to: Business * H-D or Harley-Davidson, a motorcycle manufacturer * The Home Depot, NYSE stock symbol: HD Chemistry * Hydrogen deuteride, a diatomic compound of hydrogen and deuterium * Mustard gas Codes * Air Do, formerly Ho ...

(MY Serpentis) is a

Beta Lyrae variable Beta Lyrae variables are a class of close binary stars. Their total brightness is variable star, variable because the two component stars orbit each other, and in this orbit one component periodically passes in front of the other one, thereby bloc ...

triple system consisting of three very hot

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

s. A member of the cluster

NGC 6604 NGC 6604 is a young open cluster of stars in the equatorial constellation of Serpens, positioned about 1.5° north of the Eagle Nebula (NGC 6611). The cluster was discovered by William Herschel on July 15, 1784. It is located at a distance of 4 ...

, 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 temperatures of supergiant stars range ...

of a late O or early B spectral type. Also an eclipsing binary, the

HD 166734 HD may refer to: Business * H-D or Harley-Davidson, a motorcycle manufacturer * The Home Depot, NYSE stock symbol: HD Chemistry * Hydrogen deuteride, a diatomic compound of hydrogen and deuterium * Mustard gas Codes * Air Do, formerly Ho ...

system consists of two O-type blue supergiants in orbit around each other. Less extreme in terms of mass and temperature is

HD 161701 HD may refer to: Business * H-D or Harley-Davidson, a motorcycle manufacturer * The Home Depot, NYSE stock symbol: HD Chemistry * Hydrogen deuteride, a diatomic compound of hydrogen and deuterium * Mustard gas Codes * Air Do, formerly Ho ...

, 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; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

and an Ap star. South of the

on the border with Sagittarius is the eclipsing binary

W Serpentis W Serpentis is an eclipsing binary star in the constellation Serpens. It is always too faint to be seen with the naked eye, varying between apparent magnitudes 8.42 and 10.2 with a period of just over 14 days. This is mainly due to ecli ...

, 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 most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and ...

, and was one of the first discovered Serpentids, which are eclipsing binaries containing exceptionally strong

far-ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of the ...

spectral lines. It is suspected that such Serpentids are in an earlier evolutionary phase, and will evolve first into

double periodic variable A Double Periodic Variable (DPV) is a type of binary star. As the name implies, the systems vary in brightness not only due to eclipses of one star by the other, but also on a cycle of roughly 33 times longer than the orbit. The star gaining mass f ...

s and then classical Algol variables. Also near the Eagle Nebula is the eclipsing Wolf–Rayet binary

CV Serpentis CV Serpentis is a binary star system in the equatorial constellation of Serpens. It is a detached eclipsing binary with an orbital period of 29.7 days. The system includes a Wolf–Rayet (WR) star with the identifier WR 113. The sy ...

, 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 An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelengt ...

. One of these,

GX 17+2 GX, Gx, or gx may refer to: Airlines * Guangxi Beibu Gulf Airlines (IATA airline designator GX) * Air Ontario (1983-2001, former IATA airline designator GX) * JetMagic (2003-2004, former IATA airline designator GX) Arts, entertainment, and me ...

, 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 common main sequence star), to the other component, called the ''acc ...

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 William Stephen Finsen FRAS (28 July 1905 – 16 May 1979) was a South African astronomer. He discovered a number of double stars and took many photographs of Mars. He developed the Finsen eyepiece interferometer to measure very close double s ...

, who was struck by the nearly identical position angles and separations at the time of his 1953 discovery.

Gliese 710 Gliese 710, or HIP 89825, is an orange star in the constellation Serpens Cauda. It is projected to pass near the Sun in about 1.29 million years at a predicted minimum distance of 0.051 parsecs— (about 1.6 trillion km)—about 1/25th o ...

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 5 Serpentis is a wide binary star system in Serpens Caput, the western section of the equatorial constellation of Serpens. It is faintly visible to the naked eye with an apparent visual magnitude of 5.10. Based upon an annual parallax s ...

. 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 pulsar A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio pulsar, radio, X-ray pulsar, X-ray, and gamma ray portions of the electromagnetic spectrum. The leadi ...

s, one of which is in a binary, allowing the

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

of the cluster to be measured. The binary could help our understanding of

neutron degenerate matter Degenerate matter occurs when the Pauli exclusion principle significantly alters a state of matter at low temperature. The term is used in astrophysics to refer to dense stellar objects such as white dwarfs and neutron stars, where thermal pressu ...

; the current median mass, if confirmed, would exclude any "soft"

equation of state In physics and chemistry, 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 internal energy. Most mo ...

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

magnetic dipole moment In electromagnetism, the magnetic moment or magnetic dipole moment is the combination of strength and orientation of a magnet or other object or system that exerts a magnetic field. The magnetic dipole moment of an object determines the magnitude ...

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

axion An axion () is a hypothetical elementary particle originally theorized in 1978 independently by Frank Wilczek and Steven Weinberg as the Goldstone boson of Peccei–Quinn theory, which had been proposed in 1977 to solve the strong CP problem ...

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

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

in 1791. Another globular cluster is

Palomar 5 Palomar 5 is a globular cluster in the constellation Serpens and a member of the Palomar Globular Clusters group. It was discovered by Walter Baade in 1950, and independently found again by Albert George Wilson in 1955. After the initial name of ...

, 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 L183 or L134N is a much-studied pre-stellar core in the constellation Serpens Cauda 360 light-years away. This massive accumulation of gas and dust was the interstellar object in which the phenomenon of coreshine Coreshine is an astronomical ter ...

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 ...

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 NGC 5962 is a spiral galaxy in the celestial equator, equatorial constellation of Serpens Caput. It was discovered by the Anglo-German astronomer William Herschel on March 21, 1784. The NGC 5962 galaxy is located at a distance of 120 million ...

, a

spiral galaxy Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''

positioned around 28 megaparsecs distant 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 NGC 5921 is a barred spiral galaxy located approximately 65 million light-years from the Solar System in the constellation Serpens Caput. It was discovered by William Herschel on 1 May 1786. In February 2001 a type II supernova ( SN 2001X) was dis ...

, 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 in the local universe, and generally affect both the motions of stars and interstellar gas ...

with a

LINER Liner or LINER may refer to: Line drawing * Eye liner, a type of makeup * Marker pen, a porous-tip pen with its own ink source * Multiple lining tool used in engraving * A sable brush used by coach painters Linings * Acoustic liner, a no ...

-type

active galactic nucleus An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such e ...

situated somewhat closer at a distance of 21 megaparsecs. A

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

was observed in this galaxy in 2001 and was designated SN 2001X. Fainter still are the spirals

NGC 5964 NGC 5964 is a barred spiral galaxy in the constellation Serpens Caput. NGC 5964 is also known by the names IC 4551 and PGC 55637. NGC 5964 has relatively unwound spiral arms; it lacks the clear defined spiral arms the Milky Way galaxy has. The ...

and

NGC 6118 NGC 6118 is a grand design spiral galaxy located 83 million light-years away in the constellation Serpens (the Snake). It was discovered on 14 April 1785 by German-British astronomer William Herschel. NGC 6118 measures roughly 110,000 light-years ...

, with the latter being host to the

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

SN 2004dk. Hoag's Object, 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

, 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 interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

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 emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such e ...

, with the former a

Seyfert 2 galaxy Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei (very luminous sources of electromagnetic radiation that are outside of our own galaxy) with very high surface ...

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 iden ...

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 * Cluster II (spacecraft), a European Space Agency mission to study the magnetosphere * Asteroid cluster, a small ...

lies at a distance of 190 million

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from Earth and is approximately 100,000 light-years across, making Seyfert's Sextet one of the densest galaxy groups known. Astronomers predict that the four interacting galaxies will eventually

merge Merge, merging, or merger may refer to: Concepts * Merge (traffic), the reduction of the number of lanes on a road * Merge (linguistics), a basic syntactic operation in generative syntax in the Minimalist Program * Merger (politics), the comb ...

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 three main galaxy morphological classification, classes of galaxy described by Edwin Hubble in his Hub ...

. The radio source

3C 326 3C may refer to: In astronomy: * 3C, the ''Third Cambridge Catalogue of Radio Sources'', an astronomical reference series In business: * 3C Records * 3C (radio), a defunct digital radio station * 3C (trade association), an American trade associ ...

was originally thought 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 Abell may refer to: People *Abell (surname) * George O. Abell, of the astronomical catalogues fame Places ;United States * Abell, Maryland, a location in St. Mary's County, Maryland * Abell, a neighborhood in Baltimore, Maryland * Abells Corners, ...

. The cluster is thought to be interacting with the nearby galaxy group

MKW 3s MKW or variations may refer to: * ''Mario Kart Wii'', a 2008 kart racing video game developed and published by Nintendo for the Wii * ''Mario Kart World'', a 2025 kart racing video game by Nintendo for the Nintendo Switch 2 * MKW, the IATA code for ...

, 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, the ...

at the center of Abell 2063. The active galaxy at the center of MKW 3s—

NGC 5920 NGC 5920 is a large lenticular galaxy located in the Serpens constellation. Discovered on March 30, 1887, by American astronomer Lewis Swift, NGC 5920 is 711 million light-years distant from planet Earth. It is a narrow-line radio galaxy and about ...

—appears to be creating a bubble of hot gas from its radio activity. Near the 5th-magnitude star

Pi Serpentis Pi Serpentis, Latinized from π Serpentis, is a solitary white-hued star in the constellation Serpens, located in its head, Serpens Caput. Based upon an annual parallax shift of 18.22 mas as seen from Earth, it is located around 179 ...

lies

AWM 4 AWM may refer to: *Academies of West Memphis, a public high school in West Memphis, Arkansas * Appliance Wiring Material, covered by UL standard 758 *Apostolic Women's Ministries, an organization that serves the women of the Apostolic Church of Pent ...

, a cluster containing an excess of metals in the

intracluster medium In astronomy, the intracluster medium (ICM) is the superheated plasma (physics), plasma that permeates a galaxy cluster. The gas consists mainly of ionized hydrogen and helium and accounts for most of the baryonic material in galaxy clusters. The ...

. 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 3C may refer to: In astronomy: * 3C, the ''Third Cambridge Catalogue of Radio Sources'', an astronomical reference series In business: * 3C Records * 3C (radio), a defunct digital radio station * 3C (trade association), an American trade associ ...

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

s, the quasar pair

4C 11.50 4C may refer to : * "4C" (''Person of Interest''), an episode of the TV series ''Person of Interest'' * 4C Array, a cylindrical paraboloid radio telescope at the Mullard Radio Astronomy Observatory * 4C Entity, a consortium to establish a platform ...

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 ...

. An example of

gravitational lens A gravitational lens is matter, such as a galaxy cluster, cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's Ge ...

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: * 3C Records * 3C (radio), a defunct digital radio station * 3C (trade association), an American trade associ ...

. 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 A dust lane consists of relatively dense, obscuring clouds of interstellar dust, observed as a dark swath against the background of brighter object(s), especially a galaxy. These dust lanes can usually be seen in spiral galaxies, such as the M ...

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 l ...

PG 1553+113 PG, P.G., P&G, pg, or Pg, or similar, may refer to: *Parental Guidance (PG), a content rating in the following motion picture content rating systems and television content rating systems: ** Australian Classification Board ** Film Censorship Boar ...

is a heavy emitter of

gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

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 extremely energetic events occurring in distant Galaxy, galaxies which represent the brightest and most powerful class of explosion in the universe. These extreme Electromagnetic radiation, ele ...

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 the Milky Way 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 Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...

. 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

. 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 base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...

s and produce prodigious amounts of radiation that will eventually

destroy Destroy may refer to: * ''Destroy'' (album), a 2004 album by Ektomorf * Destroy!, a Minneapolis Crust punk band * '' Destroy!!'', a comic book by Scott McCloud See also * Destroyer (disambiguation) * Destruction (disambiguation) * Destroy 2 ...

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 globule An evaporating gas globule (EGG) is a region of hydrogen gas in outer space approximately 100 astronomical units in size, such that gases shaded by it are shielded from ionizing UV rays. Dense areas of gas shielded by an evaporating gas globule c ...

s; unlike

Bok globule In astronomy, Bok globules are isolated and relatively small dark nebulae containing dense cosmic dust and gas from which star formation may take place. Bok globules are found within H II regions, and typically have a mass of about two to 50 sol ...

s they only hold one

protostar A protostar is a very young star that is still gathering mass from its parent molecular cloud. It is the earliest phase in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. The p ...

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

OB association The Ob (; ) is a major river in Russia. It is in western Siberia, and with its tributary the Irtysh forms the world's seventh-longest river system, at . The Ob forms at the confluence of the Biya and Katun which have their origins in the Al ...

Serpens OB2 Serpens () is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International Astronomical Union. It ...

, 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 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 of light year ...

S 54. Within this HII region is the open cluster

, 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 A galactic disc (or galactic disk) is a component of disc galaxies, such as spiral galaxies like the Milky Way and lenticular galaxies. Galactic discs consist of a stellar component (composed of most of the galaxy's stars) and a gaseous component ...

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 a galaxy comprise its halo: * the stellar halo * the galactic corona (hot gas, i.e. a plas ...

. Another

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

in Serpens Cauda is

, containing at least one naked-eye star, HD 172365 (another naked-eye star in the vicinity,

HD 171586 HD may refer to: Business * H-D or Harley-Davidson, a motorcycle manufacturer * The Home Depot, NYSE stock symbol: HD Chemistry * Hydrogen deuteride, a diatomic compound of hydrogen and deuterium * Mustard gas Codes * Air Do, formerly Ho ...

, 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 NGC 6535 is a globular cluster of stars located at a distance of 22,200 light years from Earth in the equatorial constellation of Serpens, and is listed in the ''New General Catalogue''. Its discovery is usually attributed to astronomer Jo ...

, 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 MWC may refer to: Organisations * Mark Williams Company, a software company * Mennonite World Conference, a global community of Christian churches * Midwest Conference, a U.S. college athletic conference * Mountain West Conference, another U.S. col ...

is a star surrounded by a

planetary nebula A planetary nebula 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 unrelated to planets. The ...

. Dubbed the

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 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 in 1604. Light and neutrinos ...

. 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 ex ...

, meaning that it is a Be star containing exceptionally bright

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

emission line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

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 Abell may refer to: People *Abell (surname) *George O. Abell, of the astronomical catalogues fame Places ;United States * Abell, Maryland, a location in St. Mary's County, Maryland * Abell, Baltimore, Abell, a neighborhood in Baltimore, Maryland ...

, 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 The Infrared Astronomical Satellite (Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mon ...

. 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 stellar atmosphere, 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 spheri ...

s, and it has been proposed that this object is in transition between class 0 and class I. A

variable nebula Variable nebulae are reflection nebulae that change in brightness because of changes in their star. See also *McNeil's Nebula *NGC 1555 (Hind's Variable Nebula) *NGC 2261 NGC 2261 (also known as Hubble's Variable Nebula or Caldwell 46) is a v ...

exists around the protostar, although it is only visible in infrared light. The

Serpens cloud Serpens () is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International Astronomical Union. It ...

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 The Serpens South star cluster is a relatively dense group of more than 600 young stars, dozens of which are protostars just beginning to form. The cluster is situated in the southern portion of the Serpens cloud (adjacent to the star-forming reg ...

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, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicate ...

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 fundame ...

. Despite the presence of the Milky Way, several active galaxies are visible in Serpens Cauda as well, such as

PDS 456 PDS 456 is a relatively nearby radio-quiet quasar located in the constellation of Serpens. This is a luminous active galactic nucleus (AGN) with a redshift of (z) 0.184, first discovered by astronomers conducting the Pico dos Dias survey in 1997. ...

, 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 NRAO 530 or PKS 1730-13 is a flat-spectrum radio quasar located in the southern constellation of Serpens. It has a redshift of 0.902. and was first discovered by two astronomers, W.J. Welch and Hyron Spinrad in 1973. It is classified as a blazar ...

, 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 the ...

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 (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...

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 ext ...

s that radiate from Serpens, the

Omega Serpentids Omega (, ; uppercase Ω, lowercase ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and last letter in the Greek alphabet. In the Greek numeric system/isopsephy (gematria), it has a value of 800. The wo ...

and the

Sigma Serpentids Sigma ( ; uppercase Σ, lowercase σ, lowercase in word-final position ς; ) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used as an operator ...

. 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