Constellations: Serpens 'the Serpent' Content from the guide to life, the universe and everything

Constellations: Serpens 'the Serpent'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
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Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus
Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula

Name:Serpens (Latin: 'snake')
Short form:Ser
Area:637 sq deg
Co-ordinates1:Serpens Caput: 16h, +10°Serpens Cauda: 18h, −05°

Serpens is the only constellation to occupy two separate portions of the sky, representing the snake which Ophiuchus 'the serpent bearer' has draped across his shoulders and divided by his torso. Serpens Caput is the head of the snake and Serpens Cauda is the tail. For the purposes of this Entry we shall treat Serpens as one constellation but reference each object separately.

Serpens Caput is the more northern of the two sections, containing the most listed stars. Caput shares its borders with Corona Borealis, Boötes, Virgo, Libra, Ophiuchus and Hercules. Serpens Cauda has borders with Aquila, Ophiuchus, Sagittarius and Scutum.


A snake entwined around a staff or rod is found on the symbol of medicine worldwide. Legend has it that the rod belonged to Asclepius2, the demigod3 of healing, who learned how to treat the sick from watching a snake bring herbs to its ailing brother. Asclepius became so skilled he actually brought someone back to life, which shocked the gods who jealously guarded their power. They could not allow the humans to live forever, so Asclepius was doomed. Zeus, the king of the gods, killed him with a thunderbolt. However, Zeus then honoured Asclepius and his beloved snakes by creating their image in the heavens, conjoined for all eternity as Ophiuchus the serpent bearer and Serpens.

The caduceus (magic wand) held by Mercury (Hermes in Greek), the winged messenger of the gods, is described as a rod with a pair of attached wings and two intertwined serpents. The caduceus (Greek: kerykeion) appears in many cultures with various meanings, but mostly it represents a symbol of immortality.


The scientific star names are simple to understand (if you know your Greek alphabet), the 'alpha' star means that it is the brightest star in that constellation. Combined with the genitive name, this is known as the 'Bayer designation'. Sometimes the order of brightness doesn't agree with the listing, this could be due to error at the time of cataloguing or fluctuation on the part of the star. The star table below lists them in order of highest magnitude. Some stars have proper names as well; for example, alpha Serpentis is Unukalhai. Others are known by their catalogue numbers.

StarDesignationName or
catalogue number
Serpens Caput
or Cauda
(light years4)
Spectral classification
and/or comments
α Seralpha SerUnukalhaiCaput+2.6572Multiple star system
η Sereta SerTangCauda+3.2 var61Binary star system
μ Sermu SerLeiolepidotusCaput+3.5 var150White dwarf
β Serbeta SerZhouCaput+3.6150Multiple star system
ε Serepsilon Ser37 SerpentisCaput+3.769White dwarf
γ Sergamma Ser41 SerpentisCaput+3.8 var36White giant
θ Sertheta SerAlyaCauda+4 var130Binary star system
ν Sernu Ser53 SerpentisCauda+4 var180Binary
κ Serkappa Ser35 SerpentisCaput+4.1350Red giant
δ Serdelta SerQinCaput+4.2 var200Multiple star system
ο Seromicron Ser56 SerpentisCauda+4.2 var160Delta Scuti-type variable
ζ Serzeta Ser57 SerpentisCauda+4.6 var74Yellow-white dwarf
τ Septau Ser9 SerpentisCaput+5 var160 to 920Multiple star system
ω Seromega Ser34 SerpentisCaput+5.2250Yellow giant/has a planet

Alpha Serpentis, Unukalhai, is a multiple system representing the heart of the serpent, although unukalhai literally means 'the neck' in Arabic.

Some of the stars of Serpens are named after Chinese dynasties. One such is beta Serpentis, Chow, which is one of the three stars making up the head. Kappa Serpentis is a red giant which forms one of the snake's eyes. Gamma Serpentis is a white giant which creates the other snake eye, it lies just inside the border with Hercules.

Another named star is theta Serpentis, Alya, a binary star system in Cauda. Alya marks the tip of the serpent's tail and lies on the border with Aquila.

Tau Serpentis is a multiple system in Caput containing eight stars of varying magnitude and classification.

New General Catalogue (NGC)

The NGC catalogue was compiled by John Louis Emil Dreyer (the director of the Armagh Observatory from 1882 to 1916).

  • NGC 5953 and NGC 5954 aka Arp 91 are a pair of interacting galaxies5 inside the extreme north border, just beneath the tiara-shaped Corona Borealis.

  • NGC 5957 is a barred spiral galaxy although the arms have almost joined to form a ring.

  • NGC 6535 and NGC 6539 are globular clusters which were discovered in the 19th Century, both of them share the border with Ophiuchus.
  • NGC 6604 is an open cluster within 2° of M16 and close to the border with Scutum.

CatalogueSerpens Caput
or Cauda
TypeBrightness (m)Distance
(light years)
Arp 91CaputGalaxy pair+1280mInteracting
NGC 5953 + 5954
NGC 5957CaputGalaxy+1589mBarred spiral
NGC 6535CaudaGlobular cluster+10.522,000Discovered by Hind
in April 1852
NGC 6539CaudaGlobular cluster+9.327,000Discovered by Brorsen
in September 1856
NGC 6604CaudaOpen Cluster+6.56,000Nebulous

There are two more open clusters which were discovered too recently to be included in the NGC, both are found in Cauda. IC 4756 is 1,300 light years distant and visible magnitude +4.6. Tr 32 would be much harder for the amateur astronomer to locate due to its much lower magnitude of +12.


There is one Messier object to be noted in Cauda, the awesome Eagle Nebula (M16), and one in Caput, M5.

M5/NGC 5904

M5 is a 14 billion year old globular cluster, a tightly-packed 'ball' of stars, containing about 100,000 gravitationally-bound members. These aged 'objects' orbit the galactic centre forming a loose chain.

M16/NGC 6611

The Eagle Nebula is over 6,000 light years distant and spans 20 light years from one side to the other. This emission nebula contains the famous 'Pillars of Creation', a star factory immortalised by the Hubble Space Telescope in 1995. Also part of M16 is the fabulously photogenic open cluster.

Hoag's Object

Caution: this fabulous sight will turn a mild interest in astronomy into cosmic overload faster than you can say Mandolin Jones. Named after its discoverer the US astronomer Arthur Hoag who reported it in 1950, Hoag's Object aka PGC 54559 is an enigmatic ring galaxy. It is situated above the snake's head asterism6 in the northernmost portion of Caput, close to the border with Boötes.

Hoag's Object has a central elliptical core and an outer ring which could have been the arms of a spiral, now joined. The radius of Hoag's Object is 100,000 light years: the overall effect is rather like a sparkling brooch; at 600 million light years distant, that's one large piece of jewellery! It has such a 'wow' factor that it was the most-uploaded image at the Galaxy Zoo forum in 2007. Uncannily, in the space that we can see through, another ring galaxy can clearly be seen in the background, which could be millions of light years more distant than Hoag's Object. As ring galaxies are extremely rare, the odds against this occuring must have been astronomical, until it happened!

Dark Nebulae

Lynds Dark Nebula 183 is a dusty molecular cloud in Caput. It's one of the closest dark nebulae at just 325 light years distance. Another dark nebula in Serpens is LDN 483, which is located about 700 light years away.

Extrasolar Planets in Serpens

There have been several extrasolar planetary systems found in this constellation up to 2011; the first was discovered in 1998. Figures given in the table below are the length of the planet's orbital period around its parent star, which we know of as a year. The mass of the extrasolar planet is compared to that of Jupiter, our Solar System's largest planet, known by astronomers as the 'Jovian scale'.

HD 168443 is a yellow main sequence (dwarf) similar to our Sun. It has two satellites, a superjovian planet and a brown dwarf (failed star).

Extrasolar Planets Table

Star name or
catalogue number
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoverySerpens Caput
or Cauda
HD 168443HD 168443 b7.2581998CaudaHot superjovian
HD 168443HD 168443 c341,7422001CaudaBrown dwarf
HD 136118HD 136118 b421,2092002CaudaBrown dwarf
HD 168746HD 168746 b0.236.42000CaudaHot gas giant
HD 175541HD 175541 b0.63002007CaudaGas giant; eccentric orbit
CoRoT-9CoRoT-9 b0.8495.272010CaudaGas giant
CoRoT-11CoRoT-11 b2.532010CaudaSuperjovian
CoRoT-22CoRoT-22 b0.049.762014CaudaSuper Earth
CoRoT-23CoRoT-23 b2.83.632011CaudaSuperjovian
PSR 1719-14PSR 1719-14 b10.092011Cauda'Diamond' pulsar planet
HD 142245HD 142245 b1.91,2992011CaputSuperjovian
ω Seromega Ser b1.72772013CaputSuperjovian
HAT-P-45HAT-P-45 b0.93.132013CaudaHot Jupiter
HAT-P-46HAT-P-46 b0.5212013CaudaHot gas giant
CoRoT-27CoRoT-27 b10.43.572014CaudaSuperjovian
CoRoT-28CoRoT-28 b0.485.22015CaudaHot gas giant
CoRoT-33CoRoT-33 b59.25.82015CaudaBrown dwarf

Serpens Paraphernalia

While this Entry is mostly about the constellation Serpens, the author thought you may like some additional information on snakes and serpents.

Fear of Snakes

Some snakes are harmless7, but the fear of snakes is quite a common phobia8. Ophiophobia (or Ophidiophobia) is the name given to this fear. Some people who have no contact with snakes in their daily life are frightened of them, which is known as 'irrational fear'. Others fear the snake's ability to inflict harm or kill in their home environment. A true ophiophobic would dread even the image of a snake in a book or on a TV screen.

No Fear of Snakes

There are people who like serpents, and some even keep snakes as pets. If you don't want to go that far, you can at least have a taster by visiting somewhere like The Jungle, a popular tourist attraction in Cleethorpes, NE Lincolnshire. The Jungle is also a rescue centre, providing homes for exotic animals which have been donated or abandoned by previous owners, including snakes. Close contact with some of the animals, like the resident family of meerkats, is allowed, but the snakes are displayed safely behind glass. If you're willing to pay for the privilege, the staff will retrieve an animal so you can be photographed with it.

Snake Consumption

After a hard day of basic training, you could eat a rattlesnake9.
- Elvis Presley
  • Snake oil used to be sold at carnivals and door-to-door by disreputable salesmen who claimed it was good for whatever ails you. The key ingredient was usually alcohol.

  • Snake body parts are a component of some Chinese traditional medicines.

  • Some parts of the world consider snake flesh a delicacy. In Cantonese restaurants some of the popular dishes include Bamboo Shoots with Snake Slices, and Snake Soup (where nothing is wasted).

  • If you order a pint of 'snakebite' in a UK pub you'd get a drink consisting of half lager, half cider. Potent stuff, but nothing to do with snakes.

Serpent Stories

Snakes have played no small part in human history. It was a serpent in the Bible story Genesis which tempted Eve to partake of the fruit of the Tree of Knowledge, thus leading to human expulsion from the Garden of Eden. In the Gospel according to Mark: 'They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover' shouldn't be taken literally, as the Rev George Went Hensley paid the price of snake-handling in 1955.

Snake References

Snake references are made in generally derogatory terms, possibly stemming from the Biblical connection. Ergo, a snake in the grass is someone who is not to be trusted. Some snake terms have entered modern language, for example, an Australian person in a blind rage would be described as mad as a cut snake.

A snake in the lexicon of golf terminology is a long putt (a golf stroke) which rolls over the curvature of the green, much as a snake would slither along the ground.

There are people who like to tattoo their bodies and snakes are a powerful image, making them a popular choice of design. One such is the Kundalini, a Sanskrit word for 'coiled snake', and also translates to serpent power, which is usually engraved as if coiled around the person's backbone.

Harry Potter

Snake references abound in the magical world of 'Harry Potter'. JK Rowling gave her boy wizard the ability to speak Parseltongue (snake language), making him a 'Parselmouth'. One of the books, Harry Potter And The Chamber Of Secrets featured a gigantic snake called a Basilisk, which Harry had to do battle with. He was aided in being victorious by the phoenix which belonged to Professor Dumbledore.

Snake Entries in the Edited Guide

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2Various other spellings include Aesculapius and Asklepios.3He was the son of the god Apollo and the mortal Coronis.4A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion kms.5Astronomers refer to such events as 'cosmic trainwrecks'.6A group of stars which isn't a recognised constellation.7But not all. You would need to be careful when visiting Australia.8Phobia comes from phobos which is Greek for 'fear'.9This is a jest, akin to a British person saying they're so hungry they could eat a horse.

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