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Serpens CaputSerpens Cauda
Abbreviation Ser
Genitive Serpentis
Pronunciation /ˈsɜrpɨnz/,
genitive /sərˈpɛntɨs/
Symbolism the Snake
Right ascension Serpens Caput: 15h 10.4m to 16h 22.5m
Serpens Cauda: 17h 16.9m to 18h 58.3m
Declination Serpens Caput: 25.66° to −03.72°
Serpens Cauda: 06.42° to −16.14°
Family Hercules
Area Serpens Caput: 428 sq. deg.
Serpens Cauda: 208 sq. deg.
Total: 637 sq. deg. (23rd)
Main stars 11
Stars with planets 15
Stars brighter than 3.00m 1
Stars within 10.00 pc (32.62 ly) 2
Brightest star α Ser (Unukalhai) (2.63m)
Nearest star GJ 1224
(24.60 ly, 7.54 pc)
Messier objects 2
Serpens Caput:
Corona Borealis

Serpens Cauda:
Visible at latitudes between +80° and −80°.
Best visible at 21:00 (9 p.m.) during the month of July.

Serpens ("the Serpent", Greek Ὄφις) is a constellation of the northern hemisphere. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and it remains one of the 88 modern constellations defined by the International Astronomical Union.

It is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput (Serpent's Head) to the west and Serpens Cauda (Serpent's 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 μ Ser in Serpens Caput and ν Ser in Serpens Cauda. The brightest star in Serpens is Unukalhai or Cor Serpentis "Serpent's Heart", with an apparent magnitude of 2.63.


Serpens held by Ophiuchus, as depicted in Urania's Mirror, a set of constellation cards published in London c. 1825. Above the tail of the serpent is the now-obsolete constellation Taurus Poniatovii while below it is Scutum.

Aratus describes the constellation as follows:

Both [hands of Ophiuchus] firmly clutch the Serpent, which encircles the waist of Ophiuchus, but he, steadfast with both his feet well set, tramples a huge monster, even the Scorpion, standing upright on his eye and breast. Now the Serpent is wreathed about his two hands – a little above his right hand, but in many folds high above his left. ... Toward the Crown leans the Serpent’s jaw, but beneath his coiling form seek thou for the mighty Claws [Libra][1]

There were two "serpent" constellations in Babylonian astronomy, known as Mušḫuššu and Bašmu. It appears that Mušḫuššu was depicted as a hybrid of dragon, lion and bird, and loosely corresponds to Hydra. Bašmu was a horned serpent (c.f. Ningishzida) and loosely corresponds to the Ὄφις constellation of Eudoxus of Cnidus on which the Ὄφις (Serpens) of Ptolemy is based.[2]


Serpens Caput is bordered by Libra and to the south, Virgo and Boötes to the east, Corona Borealis to the north, and Ophiuchus and Hercules to the west; Serpens Cauda is bordered by Sagittarius to the south, Scutum and Aquila to the east, and Ophiuchus to the north and west. Covering 636.9 square degrees total, it ranks 23rd of the 88 constellations in size. It appears prominently in the both the northern and southern skies during the Northern Hemisphere's summer.[3] Its main asterism consists of 11 stars, and 108 stars in total are brighter than magnitude 6.5.[3] Serpens Caput's boundaries, as set by Eugène Delporte in 1930, are defined by a 15-sided polygon, while Serpens Cauda's are defined by a 25-sided polygon. In the equatorial coordinate system, the right ascension coordinates of Serpens Caput's borders lie between 15h 10.4m and 16h 22.5m, while the declination coordinates are between 25.66° and −03.72°. Serpens Cauda's boundaries lie between right ascensions of 17h 16.9m and 18h 58.3m and declinations of 06.42° and −16.14°.[4] The International Astronomical Union (IAU) adopted the three-letter abbreviation "Ser" for the constellation in 1922.[5]

Notable features[edit]

The constellation Serpens (Caput) as it can be seen by the naked eye.
The constellation Serpens (Cauda) as it can be seen by the naked eye.


Since Serpens is regarded as one constellation despite being split into two halves, the ordering of Bayer designations goes roughly in order of brightness among both halves (i.e. there is only one Alpha, one Beta, etc. in the entire constellation). Only one of the stars in Serpens is brighter than third magnitude, so the constellation is not easy to perceive.

Head stars[edit]

The brightest star in Serpens, Alpha Serpentis, also known as Unukalhai, is a red giant located approximately 22.68 parsecs (74.0 ly) away. With a visual magnitude of 2.63,[6] 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,[7] although it is not visible to the naked eye.

δ Serpentis is a double star 210 light-years from Earth.

Stars in the head include Alpha, Beta, Gamma, Delta, Epsilon, Iota, Kappa, Lambda, Mu, Pi, Rho, Sigma, Tau, Chi and Omega Serpentis.

Tail stars[edit]

Stars in the tail include Zeta, Eta, Theta, Nu, Xi, and Omicron Serpentis.

Deep-sky objects[edit]

Head objects[edit]

Messier 5 is a globular cluster located approximately 8° southwest of α Serpentis.

Hoag's Object is a perfectly shaped ring galaxy located 600 million light-years from Earth (redshift 0.00425). The outer ring is largely composed of young blue stars but 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 a velocity too great to keep its coherence and therefore detached.[8]

Arp 220 is another unusual galaxy in Serpens. The prototypical ultraluminous infrared galaxy, Arp 220 is located 250 million light-years from Earth (redshift 0.0181). It consists of two large spiral galaxies in the process of colliding with their nuclei orbiting at a distance of 1,200 light-years, causing extensive star formation throughout both components. It possesses a large cluster of more than a billion stars, partially covered by thick dust clouds near one of the galaxies' core.[8]

Seyfert's Sextet is a group of six galaxies, four of which are interacting gravitationally and two of which simply appear to be a part of the group despite their greater distance. The gravitationally bound cluster lies at a distance of 190 million light-years from Earth (redshift 0.0145) and is approximately 100,000 light-years across, making Seyfert's Sextet one of the densest galaxy clusters known. Astronomers predict that the four interacting galaxies will eventually merge to form a large elliptical galaxy.[8]

Tail objects[edit]

The Eagle Nebula (IC 4703) and its associated star cluster lie 7,000 light-years from Earth in the direction of the galactic center. The nebula measures 70 light-years by 50 light-years and contains the Pillars of Creation, three dust clouds that became famous for the image taken by the Hubble Space Telescope. The stars being born in the Eagle Nebula, added to those with an approximate age of 5 million years have an average temperature of 45,000 degrees Kelvin and produce prodigious amounts of radiation that will eventually destroy the dust pillars.[8] 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.[9]

MWC 922, a nebula in the Mount Wilson Catalog, is a Symmetric Bipolar Nebula notable for its appearance as a perfectly symmetrical square or rectangle. It is also known as IRAS 18184-1302, and located at RA: 18:21:16 DEC: -13:01:27, near M16 in Serpens Cauda. The MWC is from Mount Wilson Observatory.

Part of the Milky Way passes through the tail, as illustrated by the shaded regions of the star map.

The Serpens South star cluster was uncovered by NASA's Spitzer Space Telescope in the southern portion of the Serpens cloud. The discovery was possible due to the infrared observation capabilities of the SST because at visible wavelengths the stars are completely obscured by interstellar dust in the Serpens cloud.

Meteor showers[edit]

There are two daytime meteor showers that radiate from Serpens, the Omega Serpentids and the Sigma Serpentids. Both showers peak between December 18th and December 25th.[10]


USS Serpens (AK-97) was a United States Navy Crater class cargo ship named after the constellation.


  1. ^ trans. Mair, A. W. & G. R. Loeb Classical Library Volume 129. London: William Heinemann, 1921.[1]
  2. ^ Gavin White, Babylonian Star-Lore (2007), p. 180.
  3. ^ a b Ridpath, Ian. "Constellations: Andromeda–Indus". Star Tales. self-published. Retrieved 1 April 2014. 
  4. ^ "Caelum, Constellation Boundary". The Constellations (International Astronomical Union). Retrieved 20 April 2014. 
  5. ^ Russell, H. N. (1922). "The New International Symbols for the Constellations". Popular Astronomy 30: 469–71. Bibcode:1922PA.....30..469R. 
  6. ^ "* Alpha Serpentis – Star in double system". SIMBAD. Retrieved 18 April 2014. 
  7. ^ Eggleton, P. P.; Tokovinin, A. A. (2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society 389 (2): 869. doi:10.1111/j.1365-2966.2008.13596.x.  edit
  8. ^ a b c d Wilkins, Jamie; Dunn, Robert (2006). 300 Astronomical Objects: A Visual Reference to the Universe (1st ed.). Buffalo, New York: Firefly Books. ISBN 978-1-55407-175-3. 
  9. ^ Levy 2005, pp. 112-113.
  10. ^ Jenniskens, Peter (September 2012). "Mapping Meteoroid Orbits: New Meteor Showers Discovered". Sky & Telescope: 24. 

External links[edit]

Coordinates: Sky map 17h 00m 00s, +03° 00′ 00″