Ophiuchus constellation lies in the southern sky, on the celestial equator. Its name means “the serpent bearer” in Greek.
It is pronounced /ˌɒfiːˈjuːkəs/ (off-ee-YOO-cuss). The constellation is associated with the figure of Asclepius, the famous healer in Greek mythology. It was one of the constellations first catalogued by the Greek astronomer Ptolemy in the 2nd century. Sometimes, it is also known by its Latin name, Serpentarius. Ophiuchus is generally depicted as a man holding a snake, represented by the neighboring constellation Serpens, which is divided into two parts by Ophiuchus: Serpens Caput, the snake’s head, and Serpens Cauda, the snake’s tail. The snake is usually depicted coiled around his waist.
Even though Ophiuchus is one of the constellations that cross the ecliptic and there have been attempts to include it among the signs of the zodiac, it does not belong to the Zodiac family, but to the Hercules family of constellations.
Ophiuchus contains a number of notable stars, including Rasalhague, Barnard’s Star, and Kepler’s Supernova, and many famous deep sky objects, including the Twin Jet Nebula, the Little Ghost Nebula, the dark nebulae Barnard 68, the Pipe Nebula, the Snake Nebula, and the Dark Horse Nebula, and the globular clusters Messier 9, Messier 10, Messier 12, Messier 14, Messier 19, Messier 62, and Messier 107.
Facts, location and map
Ophiuchus is the 11th largest constellation in the sky, occupying an area of 948 square degrees. It is one of the 15 equatorial constellations. It is located in the third quadrant of the southern hemisphere (SQ3) and can be seen at latitudes between +80° and -80°. The neighboring constellations are Aquila, Hercules, Libra, Sagittarius, Scorpius and Serpens.
The constellation name Ophiuchus is pronounced /ˌɒfiˈjuːkəs/. In English, the constellation is known as the Serpent Bearer. The genitive form of Ophiuchus, used in star names, is Ophiuchi (pronunciation: /ˌɒfiˈjuːkaɪ/). The three-letter abbreviation, adopted by the International Astronomical Union (IAU) in 1922, is Oph.
The brightest star in the constellation is Rasalhague, Alpha Ophiuchi, with an apparent magnitude of 2.08. There are four meteor showers associated with the constellation: the Ophiuchids, the Northern May Ophiuchids, the Southern May Ophiuchids and the Theta Ophiuchids.
Ophiuchus belongs to the Hercules family of constellations, along with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hercules, Hydra, Lupus, Lyra, Sagitta, Scutum, Sextans, Serpens, Triangulum Australe and Vulpecula.
Ophiuchus contains seven Messier objects: Messier 9 (M9, NGC 6333), Messier 10 (M10, NGC 6254), Messier 12 (M12, NGC 6218), Messier 14 (M14, NGC 6402), Messier 19 (M19, NGC 6273), Messier 62 (M62, NGC 6266) and Messier 107 (M107, NGC 6171). It also has seven stars with known planets.
The constellation contains 11 named stars. The proper names of stars that have been officially approved by the International Astronomical Union (IAU) are Barnard’s Star, Cebalrai, Guniibuu, Mahsati, Marfik, Rasalhague, Rosalíadecastro, Sabik, Timir, Yed Posterior, and Yed Prior.
Ophiuchus is most frequently associated with the Greek mythical figure of Asclepius, son of the god Apollo, who was said to be able to bring people back to life with his healing powers. Asclepius learned how to do this after seeing one snake bringing healing herbs to another. This happened when Glaucus, the son of King Minos of Crete, fell into a jar of honey and drowned. Asclepius saw a snake slithering toward his body and did away with it. Then another snake came along and placed a herb on the first one, which miraculously brought the first snake back to life. Asclepius saw this and took the same herb and placed it on Glaucus’ body. The king’s son was miraculously resurrected.
Asclepius was raised by Chiron, the wise centaur, associated with Centaurus constellation, who taught him the art of healing. In one of the myths, Asclepius was given the blood of the Gorgon Medusa by the goddess Athene. The Gorgon’s blood from the veins on her left side was poison, but the blood from the veins on the right side was said to be able to bring people back to life.
In another tale, Asclepius resurrected Theseus’ son Hippolytus after the king’s son was thrown from his chariot. In this version of the myth, Hippolytus is associated with Auriga constellation, the charioteer.
The healer was struck down by Zeus because the god was worried that the human race would become immortal with Asclepius around to heal them. Zeus’ brother Hades, the god of the Underworld, was concerned that the flow of souls into his domain would dry up as a result of Asclepius’ healing ability. Hades complained about this to Zeus and the thunder god struck the healer down with a bolt of lightning. Zeus later placed Asclepius’ image in the sky to honour his gift and good deeds. The healer became the constellation Ophiuchus, the Serpent Bearer.
Ophiuchus constellation may be descended from an ancient Babylonian constellation that represented the serpent-god Nirah, who was sometimes depicted as a hybrid being, with a human head and torso, and serpents for legs. This theory, however, has not been confirmed by sufficient evidence.
The constellation got a notable mention in John Milton’s Book 2 of Paradise Lost, in which Satan was compared to a comet “that fries the length of Ophiuchus huge/In th’ arctic sky.”
Rasalhague – α Ophiuchi (Alpha Ophiuchi)
Rasalhague (or Ras Alhague) is the brightest star in Ophiuchus. It has an apparent magnitude of 2.07 and is approximately 48.6 light years distant from Earth. It is a binary star with an orbital period of 8.62 years.
The primary component in the system is a white giant star with the stellar classification of A5 III. It has a mass 2.4 times that of the Sun. The companion is an orange main sequence dwarf (K5-7 V) with 85 percent of the Sun’s mass.
The brighter component is about 25 times more luminous than the Sun. It is a very fast spinner, with a projected rotational velocity of 240 km/s. As a result, it has an equatorial bulge that is about 20 percent larger than the polar radius, which gives Alpha Ophiuchi the shape of an oblate spheroid.
The star’s traditional name, Rasalhague, is derived from the Arabic raʾs al-ḥawwἄ, which means “the head of the serpent collector.” The star marks Asclepius’ head.
Sabik – η Ophiuchi (Eta Ophiuchi)
Sabik, Eta Ophiuchi, is the second brightest star in the constellation. It has a combined visual magnitude of 2.43 and is approximately 88 light years distant from the Sun. It is a binary star that is not easy to resolve in smaller telescopes. The system is composed of two white main sequence dwarfs belonging to the spectral classes A1 V and A3 V. They have an orbital period of 87.58 years. The stars have apparent magnitudes of 3.05 and 3.27.
ζ Ophiuchi (Zeta Ophiuchi)
Zeta Ophiuchi is the third brightest star in Ophiuchus. It is an exceptionally large blue main sequence star with the stellar classification of O9.5 V. It has an apparent magnitude of 2.569 and is about 366 light years distant from the solar system.
The star is classified as a Beta Cephei variable, a star that exhibits variations in brightness as a result of pulsation of its surface. Within the next few million years, the star will expand into a red supergiant and likely go out as a supernova, leaving behind a pulsar or neutron star.
Zeta Ophiuchi has 8 times the Sun’s radius and more than 19 solar masses. It is a fast rotating star, spinning close to the velocity at which it could begin to break up. Its projected rotational velocity may be as high as 400 km/s. The star’s estimated age is only 3 million years.
Yed Prior – δ Ophiuchi (Delta Ophiuchi)
Delta Ophiuchi is a red giant with the stellar classification of M0.5 III. It is the fourth brightest star in the constellation. It has an apparent magnitude of 2.75 and is approximately 171 light years distant from the Sun.
It forms an optical double with the star Epsilon Ophiuchi, or Yed Posterior. The word “yed” comes from Arabic and means “the hand.” The two stars mark the left hand of the Serpent Bearer, which holds the head of the serpent.
Delta Ophiuchi has a mass 1.5 times that of the Sun and a radius about 59 times solar. It is a suspected variable star with possible variations in magnitude by 0.03.
Celbalrai – β Ophiuchi (Beta Ophiuchi)
Beta Ophiuchi is an orange giant star belonging to the spectral class K2 III. It is the fifth brightest star in the constellation. It has a visual magnitude that ranges from 2.75 to 2.77 and is 81.8 light years distant from Earth. The star’s traditional name, Celbalrai (and variants Cheleb and Kelb Alrai) comes from the Arabic kalb al-rā‘ī, which means “the shepherd dog.”
Celbalrai has 113 percent of the Sun’s mass and a radius 12.42 times solar. The star is 63.4 times more luminous than the Sun. It has an unconfirmed planetary companion in its orbit.
κ Ophiuchi (Kappa Ophiuchi)
Kappa Ophiuchi is another suspected variable star in Ophiuchus. It is an orange giant with the stellar classification of K2 III. It has a mean apparent magnitude of 3.20 and is 91.5 light years distant from the Sun.
Kappa Ophiuchi has 119 percent of the Sun’s mass and 11 times the solar radius. It is 46 times more luminous than the Sun.
Yed Posterior – ε Ophiuchi (Epsilon Ophiuchi)
Epsilon Ophiuchi is a yellow giant star belonging to the spectral class G9.5 IIIb. It has a visual magnitude of 3.220 and is 106.4 light years distant from the solar system. It is 1.85 times more massive than the Sun and has a radius 10.39 times solar. The star is 54 times more luminous than the Sun. Its estimated age is about a billion years.
θ Ophiuchi (Theta Ophiuchi)
Theta Ophiuchi is a multiple star system that marks Ophiuchus’ right foot. It has an apparent magnitude of 3.26 and is approximately 436 light years distant from the solar system.
The primary component in the system is a spectroscopic binary with the stellar classification of B2 IV, matching the spectrum of a blue-white subgiant star. It is 5,000 times more luminous than the Sun. The star is classified as a Beta Cephei variable.
Sinistra – ν Ophiuchi (Nu Ophiuchi)
Nu Ophiuchi is an orange giant with the stellar classification of K0 IIIa CN-1. It has an apparent magnitude of 3.332 and is approximately 151 light years distant from the Sun. The star is three times more massive than the Sun, has 14 times the solar radius, and is 123 times more luminous than the Sun.
A brown dwarf was discovered orbiting the star in early 2004. The dwarf has a mass at least 21.9 times that of Jupiter and orbits the star with a period of 536 days. In 2010, another brown dwarf companion was discovered, one with at least 24.5 Jupiter masses and an orbital period of 3,169 days.
The star’s traditional name, Sinistra, means “the left side” in Latin.
γ Ophiuchi – Gamma Ophiuchi
Gamma Ophiuchi is a white main sequence dwarf with the stellar classification of A0 V. It has a visual magnitude of 3.75 and is approximately 95 light years distant from Earth. The star’s estimated age is about 184 million years.
Gamma Ophiuchi has a mass 2.9 times that of the Sun, a radius 1.8 times solar, and is 29 times more luminous than the Sun. The star is radiating an excess emission of infrared, which indicates the presence of a circumstellar disk of dust in its orbit.
Marfik – λ Ophiuchi (Lambda Ophiuchi)
Marfik, Lambda Ophiuchi, is a triple star system in Ophiuchus. It has a combined apparent magnitude of 3.90 and is about 170 light years distant from the solar system. The star’s traditional name, Marfik, means “the elbow” in Arabic.
Lambda Ophiuchi is a suspected variable. It has the stellar classification of A0V+A, matching the spectrum of a white main sequence dwarf.
67 Ophiuchi is a blue-white supergiant with the stellar classification of B5Ib. It has an apparent magnitude of 3.93 and an absolute magnitude of -4.26. The star is approximately 1,400 light years distant from Earth. It is a member of the open cluster Collinder 359.
70 Ophiuchi is a binary star in Ophiuchus. It is only 16.58 light years distant from the Sun. The primary component in the system is an orange dwarf with the stellar classification of K0V. It has an apparent magnitude of 4.03. It is classified as a BY Draconis type variable, a star showing variations in brightness as a result of rotation coupled with star spots and other chromospheric activity.
The companion is another orange dwarf. It has the stellar classification K4V and an apparent magnitude of 6.00. The two stars have an orbital period of 88.3 years.
χ Ophiuchi (Chi Ophiuchi)
Chi Ophiuchi has the stellar classification of B2Vne. It is a Be star, a star that radiates emissions from hydrogen which are indicative of a circumstellar ring of gas. It has an apparent magnitude that ranges from 4.18 to 5.0 and is classified as a Gamma Cassiopeiae type variable.
The star has a mass 10.1 times that of the Sun and a radius 4.5 times solar. It is 200,000 times more luminous than the Sun. Its estimated age is 22.5 million years.
36 Ophiuchi is a triple star system only 19.5 light years from Earth. The three stars have apparent magnitudes of 5.29, 5.33 and 6.34. All three are orange dwarfs and have stellar classifications of K0 V, K1 V, and K5 V. The primary and secondary components are separated by 4.6 seconds of arc, and the tertiary star is separated from the main pair by 700 arc seconds. The third component is classified as an RS Canum Venaticorum variable, a close binary star with an active chromosphere that can cause large stellar spots, which in turn cause variations in brightness.
51 Ophiuchi is a blue-white giant star belonging to the stellar class B9.5IIIe. It has a visual magnitude of 4.81 and is approximately 410 light years distant from the solar system. The star has a disk of dust that seems to be a young debris disk, likely a planetary system entering the last stage of planet formation.
12 Ophiuchi is an orange main sequence dwarf with the stellar classification of K2V. It has an apparent magnitude of 5.77 and is 31.8 light years distant from the Sun. It is classified as a BY Draconis type variable.
12 Ophiuchi has 91 percent of the Sun’s mass, 84 percent of the solar radius, and only 39 percent of the Sun’s luminosity. It was one of the top 100 target stars for the Terrestrial Planet Finder mission before the mission was postponed indefinitely.
Barnard’s Star is a red dwarf with the stellar classification of M4Ve. It has a visual magnitude of 9.54 and is only 5.980 light years distant from Earth. It is the fourth closest known individual star to the Sun. The only known stars that are closer to us are the three components of the Alpha Centauri system in Centaurus constellation. The star is too faint to be seen without a telescope.
Barnard’s Star was named after the American astronomer E. E. Barnard, who was the first to measure the star’s proper motion in 1916. The star has the largest proper motion of any star relative to the Sun, 10.3 arc seconds per year. Around the year 9,800, the star will make its closest approach to the Sun and come within 3.75 light years.
Barnard’s Star has an estimated age of 7 to 12 billion years. Despite its age, the star has been seen exhibiting an intense stellar flare, in 1998, which earned it the classification as a flare star. It is also classified as a BY Draconis variable.
GJ 1214 is a red dwarf with the stellar classification of M4.5. It has a visual magnitude of 14.71 and is 47.5 light years distant from Earth. The star has only 15.7 percent of the Sun’s mass and 20 percent of the solar radius.
A transiting extrasolar planet was discovered orbiting the star in December 2009. The planet has 6.55 Earth masses and completes an orbit around the star every 1.58 days.
Wolf 1061 is a red dwarf of the spectral type M3 V located in the Sun’s neighbourhood. It is only 13.82 light years distant and has an apparent magnitude of 10.10.
Kepler’s Supernova – Supernova 1604
Kepler’s Supernova is a remnant of a supernova that was first observed in October 1604. The German mathematician and astronomer Johannes Kepler started observing the event in Prague on October 17 and tracked it for an entire year.
The supernova occurred approximately 20,000 light years from Earth and reached a peak magnitude of -2.25 to -2.5. It was brighter than all the stars and planets in the sky, and could be seen during the day for several weeks.
Supernova 17604 was the most recent supernova in the Milky Way that could be seen by the unaided eye.
RS Ophiuchi is a recurrent nova in Ophiuchus. It has an apparent magnitude ranging from 9.6 to 13.5 in the quiet phase and reaching magnitude 5 during eruptions.
The system consists of a white dwarf and a red giant star in a close orbit. When enough material from the giant star builds up on the surface of the white dwarf – about every 20 years – the result is a thermonuclear event.
Eruptions were observed in 1898, 1933, 1958, 1967, 1985, and 2006. If the white dwarf accretes enough material to reach the Chandrasekhar limit, the maximum mass of a stable white dwarf star (1.4 solar mass), it will likely meet its end as a Type Ia supernova.
COROT-6 is a yellow-white main sequence dwarf with the stellar classification of F5V. It has a visual magnitude of 13.9 and roughly the same mass and radius as the Sun.
The star has a confirmed planet in its orbit. The planet, COROT-6b, has a mass 2.96 times that of Jupiter and completes an orbit around the star every 8.887 days.
Deep sky objects in Ophiuchus
Messier 9 (M9, NGC 6333)
Messier 9 is a globular cluster with an apparent magnitude of 8.42. It is approximately 25,800 light years distant from Earth.
It is one of the nearest globular clusters to the centre of our Galaxy, lying at a distance of 5,500 light years. The cluster was discovered by Charles Messier in 1764. The brightest stars in M9 have a visual magnitude of 13.5 and can be observed in moderately sized telescopes.
Messier 10 (M10, NGC 6254)
Messier 10 is another globular cluster in Ophiuchus. It has an apparent magnitude of 6.4 and is approximately 14,300 light years distant from the Sun. It was discovered by Charles Messier on May 29, 1764, and subsequently included in his catalogue.
The cluster’s core is quite bright and spans about 35 light years across, and the cluster’s spatial diameter spans about 83 light years.
M10 lies about 16,000 light years from the Galactic Centre and completes an orbit around the Milky Way every 140 years.
Messier 12 (M12, NGC 6218)
Messier 12 is also a globular cluster, also discovered by Messier in May 1764. It has an apparent magnitude of 7.68 and is about 15,700 light years distant from the solar system. It can be found about 3 degrees from Messier 10.
The cluster is about 75 light years in diameter, and the brightest stars in it are of 12th magnitude.
Messier 14 (M14, NGC 6402)
Messier 14 is another globular cluster, discovered by Messier in 1764. It is about 100 light years across. It has a visual magnitude of 8.32 and is 30,300 light years distant from Earth.
The cluster contains several hundreds of thousands of stars, the brightest of which are of 14th magnitude, and can easily be seen with binoculars.
Messier 19 (M19, NGC 6273)
Messier 19 is a globular cluster with an apparent magnitude of 7.47. It is approximately 28,700 light years distant from the solar system.
The cluster was discovered by Charles Messier in June 1764. It lies 4.5 degrees to the west-southwest of the star Theta Ophiuchi and can be seen with binoculars. It is located only 6,500 light years from the Galactic Centre.
The estimated age of M19 is about 11.9 billion years.
Messier 62 (M62, NGC 6266)
M62 was discovered by Charles Messier in 1771. It is another globular cluster. It has an apparent magnitude of 7.39 and is about 22,200 light years distant. The cluster is approximately 100 light years across.
Messier 107 (M107, NGC 6171)
Messier 107 is the last globular cluster entered in Messier’s catalogue. It is a relatively loose cluster with an apparent magnitude of 8.85, approximately 20,900 light years distant from Earth.
The cluster was discovered by the French astronomer Pierre Méchain in April 1782, and then independently discovered by the German-born British astronomer William Herschel in 1793.
M107 was only added to the Messier catalogue in 1947, by the Canadian astronomer Helen Sawyer Hogg.
NGC 6240 is an ultraluminous infrared galaxy (ULIRG) in Ophiuchus. It has an apparent magnitude if 12.8 and is about 400 million light years distant from the solar system. It is a remnant of a collision of two smaller galaxies, which has resulted in formation of a single larger galaxy. The galaxy has two nuclei, both active galactic nuclei (AGN), and a highly irregular structure.
IC 4665 is an open cluster with an apparent magnitude of 4.2. It is approximately 1,400 light years distant from the solar system.
The cluster has an estimated age of less than 40 million years. It can be seen with binoculars and small telescopes, and also without visual aids in exceptionally good conditions. It was discovered by the Swiss astronomer Philippe Loys de Chéseaux in 1745.
Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule about 500 light years from the Sun. It is 0.25 light years in radius and has a mass twice that of the Sun.
The cloud consists of a high concentration of molecular gas and dust, and it absorbs the visible light of the stars in the background.
NGC 6572 is a planetary nebula in Ophiuchus. It has an apparent magnitude of 8.1 and can be seen with amateur telescopes. The nebula was discovered by the German astronomer Friedrich Georg Wilhelm von Struve in 1825.
IC 4603-04 is a reflection nebula in Ophiuchus. IC 4603 lies near the bright star Antares in Scorpius constellation, and IC 4604 contains several bright stars, the brightest of which is Rho Ophiuchi. The stars that illuminate the two nebulae are 400-440 light years distant from Earth.
Little Ghost Nebula (NGC 6369)
The Little Ghost Nebula is another planetary nebula in Ophiuchus. It has an apparent magnitude of 12.9 and is about 2,000 light years distant from Earth.
The nebula was discovered by William Herschel. Its main ring structure spans about a light year across and is illuminated by the central white dwarf.
Dark Horse Nebula
The Dark Horse Nebula, sometimes known as the Great Dark Horse, is a large dark nebula in Ophiuchus.
The nebula got the name Dark Horse because its shape resembles that of a side silhouette of a horse. It is one of the largest dark nebulae in the sky. In good viewing conditions, when there is no light pollution, the nebula can be seen without binoculars.
Pipe Nebula – Barnard 59
The Pipe Nebula is a dark nebula which is part of the larger Dark Horse Nebula in Ophiuchus. It forms the hind quarters of the Dark Horse.
The nebula appears as a pipe shaped dust lane that obscures the Milky Way in the background. It can be seen without visual aids, but is best observed through binoculars.
The Pipe Nebula is approximately 600-700 light years distant from the solar system. It consists of two parts: the Pipe Stem, which is composed of Barnard 59, 65, 66 and 67, and the Bowl of the Pipe, which consists of Barnard 78.
Snake Nebula – Barnard 72
The Snake Nebula is a dark nebula approximately 650 light years from Earth. It is small, but has a distinctive S-shape of a snake, which is how it got its name.
The nebula can be found in the north-western part of the bowl of the Pipe Nebula and is part of the larger Dark Horse Nebula. It lies to the left of the molecular cloud Barnard 68.
Twin Jet Nebula (Minkowski’s Butterfly) – Planetary Nebula M2-9
The planetary nebula M2-9, also known as the Twin Jet nebula, Minkowski’s Butterfly, or the Butterfly Nebula, is another planetary nebula in Ophiuchus.
It has an apparent magnitude of 14.7 and is approximately 2,100 light years distant from the solar system. It was discovered by the German-American astronomer Rudolph Minkowski is 1947.
M2-9 is a bipolar nebula formed in the shape of twin lobes of material ejected from the central star. The shape of the lobes is believed to be caused by polar jets, which is why the nebula is sometimes called the Twin Jet Nebula.
The star at the centre of the nebula is a binary system. The primary component is the hot core of a star that ejected its outer layers and contracted into a white dwarf. The secondary component is a smaller star in a close orbit with the primary. The interaction of the two stars is what has created the nebula.
Rho Ophiuchi Cloud Complex
The Rho Ophiuchi cloud complex is another dark nebula in Ophiuchus, located a degree to the south of the star Rho Ophiuchi. The nebula is approximately 460 light years distant from Earth. It is one of the nearest star-forming regions to the Sun.
The nebula covers an area of 4.5°x6.5° and consists of two major regions of dust and gas where new stars are being formed. About 425 infrared sources, presumably young stellar objects, have been detected in one of them.
NGC 6633 is another open cluster in Ophiuchus, discovered by Philippe Loys de Chéseaux in 1745-1746. It has a visual magnitude of 4.6 and is about 1,040 light years distant from the Sun.
The cluster contains about 30 stars and is almost the size of the full Moon. It is about 660 million years old.
Palomar 6 is a globular cluster discovered by Robert G. Harrington and Fritz Zwicky. It belongs to the halo of the Milky Way Galaxy. It is a relatively loose cluster, and one of only four globular clusters known to contain a planetary nebula.
Palomar 6 is approximately 18,900 light years distant from Earth.
NGC 6304 is another globular cluster in Ophiuchus. It has an apparent magnitude of 9.03 and is approximately 19,200 light years distant from the solar system. It was discovered by William Herschel in 1786. The cluster is located near the Milky Way’s central bulge.