The Centaurus constellation is a large constellation located in the southern sky. It is also called “the Centaur.” The origin of this half-man half-horse creature can be traced back to the wondrous world of Greek mythology. Another constellation represents the same creature, Sagittarius, otherwise known as “the Archer.”
Different stories surround Centaurus. One of which, and the most famous, relates it to Chiron. Chiron was known as a wise creature who mentored well-known names in Greek mythology such as Achilles, Hercules, and Jason among others.
The constellation of Centaurus was catalogued by Claudius Ptolemy in the 2nd century along with 47 others. Many years after, it remains one of the 88 modern constellations today acknowledged by the International Astronomical Union (IAU).
9th Largest Constellation
It is one of the largest constellations that we have, occupying an area of 1,060 square degrees. With that size, it ranks as the 9th largest constellation overall. The abbreviation for this southern constellation is Cen. When talking about its stars and things related to it, we can use the genitive Centauri.
There are a great number of notable stars and deep-sky objects in Centaurus. The closest star system in our own Solar System is from this constellation. Some of the most remarkable bright stars in the sky are also there. Alpha Centauri is the 4th brightest star in the night sky while Beta Centauri is the 11th. An extraordinary star called V766 Centauri is another interesting object because it is one of the largest stars ever discovered. On top of that, some stars in Centaurus were given official names approved by the IAU.
Though it does not have Messier objects, star clusters, nebulae, and galaxies are plenty in this constellation. The bright globular cluster Omega Centauri and the galaxy Centaurus A are just some of them. There are also planetary systems that are hosted by at least 11 of its stars. Alpha Centaurids, Omicron Centaurids, and Theta Centaurids are the three meteor showers related to Centaurus.
The celestial centaur is in the constellation family of Hercules. It is the biggest group, having 19 member constellations.
- Hercules (the Kneeler)
- Ophiuchus (the Serpent Bearer)
- Ara (the Celestial Alter)
- Serpens (the Serpent)
- Sextans (the Sextant)
- Crater (the Cup)
- Corvus (the Crow)
- Hydra (the Female Water Snake)
- Centaurus (the Centaur)
- Crux (the Southern Cross)
- Lupus (the Wolf)
- Triangulum Australe (the Southern Triangle)
- Corona Australis (the Southern Crown)
- Aquila (the Eagle)
- Sagitta (the Arrow)
- Vulpecula (the Fox)
- Cygnus (the Swan)
- Lyra (the Lyre)
What’s In A Name?
The constellation that we know today as Centaurus the Centaur was known to the Babylonians as MUL.GUD.ALIM or the Bison-man. They pictured this creature as a bison with the head and torso of a man.
It was the Greeks that gave the name Centaurus to this constellation. Greek poet Aratus called it Kentauros. Another name he used for this constellation is Ippota pher, which means “the Horseman Beast.” However, the same title was used to refer to another centaur, Pholus.
The figure in the sky was interpreted by Eratosthenes as a representation of the noble centaur Cheiron. He was a common subject in classical poems. Other versions of this name in written forms are Chyron and Chiron.
What Does Centaurus Look Like?
Centaurus is outlined by many stars. There are many versions and interpretations of what this constellation looks like in the night sky. One way to help us find it is by going back to what it represents, which is the centaur.
By that, it has two arms, a man’s torso, and a lower body of a horse. The front feet are marked by two of the brightest stars in the constellation, Alpha and Beta Centauri. They are among the brightest stars in the entire sky. The two are called “pointer stars” because they serve as a guide for observers in spotting Crux. This small constellation is located just below Centaurus, near its hind legs.
The zodiac constellation of Sagittarius also represents a centaur but it looks very different from Centaurus. It contains a distinct asterism called “the Teapot” which makes the Milky Way look like its spout’s “steam.”
Where To See the Centaurus Constellation
We already know that Centaurus is in the southern sky. It is located in the southern hemisphere’s third quadrant (SQ3), at about 13 hours right ascension and -40º declination. It is visible for observers whose latitudes are between +25° and -90°
Centaurus and His Neighbors
The celestial centaur is located below the largest constellation of Hydra (the Female Water Snake). Other surrounding constellations are Antlia (the Air Pump), Vela (the Sails), Carina (the Keel), Crux (the Southern Cross), Musca (the Fly), Circinus (the Compass), Lupus (the Wolf), and Libra (the Scales).
Centaurus is often portrayed holding a spear in one of his hands. Lupus the wolf is in front of him, impaled by the weapon. It is said that the celestial wolf is to be sacrificed in the altar of the sky represented by the nearby constellation of Ara.
When To See the Centaurus Constellation
Centaurus would not be visible from every observer around the globe because of its south declination. For observers in the northern hemisphere, it is a spring constellation that is visible from late March to June. The time to see it best is around 9 pm.
The celestial centaur is circumpolar in the southern hemisphere. With that said, it is visible in locations south of the equator all year long.
Centaurus and His Stars
Centaurus is a bright constellation as a whole. When it was charted in the 2nd century, Ptolemy included just 37 stars.
Now, 281 of the stars in Centaurus have magnitudes brighter than 6.5. Some stars were officially given names approved by the IAU. These are Rigil Kentaurus, Toliman, Proxima Centauri, Hadar, Menkent, Döfida, Uklun, and Nyamien.
Alpha Centauri (α Centauri)
Alpha Centauri is a triple star system. It is the brightest star in this constellation and the 4th brightest in the sky. Not including the Sun on the list, it is the third brightest star overall, after Sirius and Canopus.
Its components are the binary Alpha Centauri AB and the third component known as Alpha Centauri C. These three stars form what is known as the closest star and planetary system to us. They lie at a distance of 4.37 light-years away from our Sun.
Alpha Centauri AB
Alpha Centauri AB is a binary that looks like a single star to our naked eye. It is very bright as its apparent magnitude is −0.27. The distance between the pair varies. It is about the same distance as the Sun and Saturn or the Sun and Pluto. They have an orbital period of 79.91 years.
Alpha Centauri A
Alpha Centauri A is officially named Rigil Kentaurus. It means “Foot of the Centaur,” referring to its location in the outline of Centaurus. It is a G-type star just like the Sun, with the stellar classification of G2V. Alpha Centauri A is 1.1 times as massive as the Sun and is 1.519 times as luminous. Its radius is also larger by roughly 22%.
Alpha Centauri B
Alpha Centauri B is also called Toliman. It is less massive than the primary, Alpha Centauri A. Its luminosity is 0.445 times that of the Sun’s. This star belongs to the spectral class K1 V.
Alpha Centauri C
Alpha Centauri C is most commonly known as Proxima Centauri. Its apparent magnitude is about 11.05, so we cannot see it in the naked eye. It has the stellar classification M6 Ve. This red dwarf is the closest member of its star system to us, located 4.24 light-years away. It hosts two exoplanets, Proxima b, and Proxima c.
Beta Centauri (β Centauri)
Beta Centauri is the second-brightest star in Centaurus. It is a multiple star system composed of three stars, traditionally called Hadar or Agena. It has an overall apparent magnitude of 0.61 and is approximately 390 light-years distant.
The components of this system are a spectroscopic binary, β Centauri A, and β Centauri B. The stars in the binary are β Centauri Aa (officially named Hadar) and β Centauri Ab. They are both in the stellar class B1 III, with a mean distance of about 4 AU. The third component is also a B-type star.
Gamma Centauri (γ Centauri)
Gamma Centauri is a binary star also known as Muhlifain. The name means “Two Things.” The components of the system are A-type stars whose combined apparent magnitude is +2.17. They have an orbital period of roughly 84.5 years. Gamma Centauri is 130 light-years from our planet.
Delta Centauri (δ Centauri)
Delta Centauri belongs to the spectral class B2 IVne. It has an apparent magnitude of +2.57. It varies between +2.51 to +2.65 in magnitude because it is a Gamma Cassiopeiae variable. Delta Centauri is 8.7 times as massive as the Sun and 5,129 as luminous. Circumstellar gas is surrounding it as it is a Be star. It is 410 light-years away from us.
Delta Centauri is also known by the name Ma Wei san, meaning “Third Star of Horse’s Tail.” It is the Chinese name of this star, referring to an asterism it forms with two other stars in the constellation, G Centauri and Rho Centauri.
Epsilon Centauri (ε Centauri)
Epsilon Centauri is a B-type star with the stellar classification B1 III. It is 430 light-years distant from us. This blue-white hued star has a mass of 11.60 solar masses. It is more luminous than the Sun by about 15,217 times. Its apparent magnitude is about +2.30. But since it is a Beta Cephei variable, it differs from +2.29 to +2.31.
Zeta Centauri (ζ Centauri)
Zeta Centauri is a binary star traditionally called Alnair. This name is from a phrase that means “Bright Body Star of the Centaur” in Arabic. Its overall apparent magnitude is +2.55. The primary star in this spectroscopic binary belongs to the spectral class B2.5 IV. Together with the other component, it has an orbital period of around eight days. Zeta Centauri is approximately 382 light-years from us.
Eta Centauri (η Centauri)
Eta Centauri is a Be star of +2.35 apparent magnitude. This main-sequence star has a stellar classification of B1.5 Vne. Its mass is approximately 12 times the Sun’s mass. It is also more luminous than the Sun by about 8,700.
Eta Centauri is a Gamma Cassiopeiae variable displaying variability of multiple periods. It is about 306 light-years away from Earth.
Theta Centauri (θ Centauri)
Theta Centauri is given the name Menkent, which means “Shoulder of the Centaur.” Its apparent magnitude is +2.06, making it the fourth brightest star in Centaurus constellation. The stellar classification of this star is K0 III. Its radius is 10.6 times the Solar radius. It radiates with the luminosity of 60 Suns. The estimated distance of Theta Centauri 58.8 light-years.
Kappa Centauri (κ Centauri)
Kappa Centauri is a spectroscopic binary of +3.14 apparent magnitude. The primary is a subgiant with the stellar classification B2 IV. It is a suspected Beta Cephei variable. This star is around seven times as massive as the Sun. Meanwhile, its companion star only has around 68% of its mass. This star is located 380 light-years away from our planet.
The star Kappa Centauri is also referred to as Ke Kwan, from its Chinese name Qí Guān sān. It means “third Star of Imperial Guards” in English. The Imperial Guards is an asterism in Chinese astronomy that Kappa Centauri forms with other stars from the Lupus constellation.
Nu Centauri (ν Centauri)
Nu Centauri is a single-lined spectroscopic binary whose combined apparent magnitude is +3.41. The primary component is a Beta Cephei variable of stellar classification B2 IV. Its tidal interaction with the other star component has made it a rotating ellipsoidal variable. The components have an orbital period of 2.622 days. Nu Centauri is more or less 437 light-years away from us.
V766 Centauri is otherwise known as HR 5171. It is a multiple star system that is among the largest stars ever known. Its components are a contact binary and a third star orbiting it.
The two components in contact are yellow star orbiting in a period of about 1,304 days. The third star belongs in the spectral class B0. It is a supergiant with a luminosity of 316,000 Suns. Even with that, it still appears fainter than the yellow hypergiant primary. HR 5171 is estimated to be 4,900 to 11,700 light-years distant.
BPM 37093 is also designated V886 Centauri. It is a ZZ Ceti type of pulsating white dwarf. It is smaller in radius and luminosity compared to the Sun but 1.10 times as massive. This 14th magnitude star is located 50 light-years from us.
Döfida is also known as HD 117618. It has the stellar classification of G0 V. We cannot see it in the naked eye because its apparent magnitude is 7.17. The mass of this main-sequence star equates to 1.10 times the Sun’s mass. It is 1.6 times as luminous.
HD 117618 has an exoplanet designated HD 117618 b. This system lies at a distance of about 124 light-years away.
Uklun is the official name given to the star HD 102117. It is a main-sequence star of G6V stellar classification. Its apparent magnitude is 7.47 so we need at least a small telescope or binoculars to see it. The age of this star is about 5.3 billion years, so it is older than our Sun.
An exoplanet, designated HD 102117b, is orbiting around Uklun in a planetary system 129 light-years distant from Earth.
WASP-15 is officially named Nyamien from the Akan mythology. It is an F-type star with an apparent magnitude of 10.9. It is hotter and more massive than the Sun.WASP-15 hosts an exoplanet, designated WASP-15b. They are approximately 1,000 light-years away from us.
Planets in the Centaur’s Constellation
More than 10 stars in the Centaurus constellation have planetary systems. Some are Super-Earths, with sizes larger than our planet but smaller than the gas giant Neptune. Others have sizes comparable to Jupiter.
Several controversial exoplanets are in the closest planetary system to us in the star Alpha Centauri. Interestingly, there is a confirmed planet close to us that is in the habitable zone.
Proxima Centauri b
Proxima Centauri b is an exoplanet larger than Earth. It has an orbital period of 11.2 days. Its mass is 1.27 times that of the Earth’s. This exoplanet lies in the habitable zone of the nearest star to us, Proxima Centauri. It orbits the red star in a period of about 11 days. It is a rocky world that can potentially support life. This super-Earth was discovered in 2016.
Proxima Centauri c
Proxima Centauri c is another super-Earth in Alpha Centauri. Unlike Proxima Centauri b, it is most probably inhabitable. Its mass equates roughly seven times the Earth’s mass. It was reported in 2019 and confirmed in 2020. It is possible that this exoplanet has a ring system.
HD 117618 b
HD 117618 b orbits around the yellow star Döfida. Its orbital period is 25.8 days. The IAU officially named it Noifasui. This exoplanet is a gas giant that is less massive than Jupiter, having a mass of about 0.1780 Jupiters. It was discovered in 2004 through radial velocity.
HD 102117 b.
HD 102117 b is a confirmed planet that belongs to the gas giant type. It was officially given the name Leklsullun. It orbits the G-type star HD 102117 (Uklun) in a period of 20.7 days. Its mass is 0.1720 times that of Jupiter’s.
PDS 70 c is a giant planet that is primarily composed of gas. It is twice as massive as the largest planet in our solar system, Jupiter. It orbits the star PDS 70 in a period of 227.5 years. The detection method used for this exoplanet is direct imaging back in 2019.
PDS 70 b is another confirmed planet that orbits the K-type star PDS 70. It is 370 light-years away from Earth. It is around three times as massive as Jupiter. Its orbital period is 119.2 years. It was discovered in 2018 through Direct Imaging.
WASP-15 b orbits the star Nyamien (WASP-15) so it is also called Nyamien b. It was officially given the name Asye. This gas giant has a mass of 0.54 Jupiters. It orbits the F-type star in 3.8 days. It was detected through the transit method.
Deep-sky Objects in Centaurus Constellation
The Centaurus constellation is home to many galaxies. The Centaurus Cluster or A3526 in itself already has hundreds of galaxies. Other celestial objects are NGC 5408, NGC 5291, NGC 5253, the open cluster NGC 3766, and a pair of interacting galaxies, NGC 5090 and NGC 5091.
Blue Planetary (NGC 3918)
NGC 3918 is nicknamed “The Blue Planetary” because of its blue appearance similar to Neptune. It is sometimes called “The Southerner.” Remnants of a dying star are in its center. This planetary nebula is 4,900 light-years from us. As its apparent magnitude is 8.5, we can see it with the help of small telescopes. It was discovered in 1834 by English astronomer John Herschel.
Omega Centauri (NGC 5139)
Omega Centauri was first identified as a star by Ptolemy. From that, Johann Bayer assigned it a Greek letter. It was rediscovered in 1677 by Edmond Halley. He found out that it was actually a non-stellar object.
Also designated NGC 5139, Omega Centauri is a large globular cluster that has about 10 million stars. It is 150 light-years across. We can see it in the naked eye as its apparent magnitude is 3.9. It is the largest of its kind in the Milky Way. Aside from that, it is also the brightest globular cluster. It is 17,090 light-years away from us.
NGC 5460 is another star cluster in Centaurus. This loose open cluster has about 272 members. The stars HD 123226 and HD 122983 are in this cluster. It is located near Zeta Centauri, approximately 2,300 light-years away from our planet.
Centaurus A (NGC 5128)
Centaurus A is a peculiar galaxy that is either lenticular or elliptical. Other designations for this celestial object are NGC 5128 and Caldwell 77. This active galaxy is the closest of its kind to us, located 11 million light-years away. With an apparent magnitude of 6.84, it is the 5th brightest galaxy that we can see in the night sky. It was discovered by James Dunlop in 1826.
Centaurus A has many star-forming regions. There is a supermassive black hole in the center of this galaxy. It is as massive as 55 million Suns. It is part of the Centaurus A/M83 Group, a group of galaxies encompassing the Centaurus, Virgo, and Hydra constellations.
NGC 4945 is designated Caldwell 83 in the Caldwell catalogue. This barred spiral galaxy is relatively close to our Milky Way, located roughly 11.7 million light-years away. It has a supermassive black hole that is more massive than a million Suns.
Meteor Showers Related to Centaurus
Three meteor showers have radiant points from Centaurus.
Alpha Centaurids occur between January 28 to February 21. The peak of its shower activity is on the 8th of February. We can expect to see about 6 meteors an hour at most during the shower. They travel at a speed of 56 km/s.
The closest star to the radiant of this meteor shower is Rigil Kentaurus. Alpha Centaurids was discovered in 1969.
Omicron Centaurids is another meteor shower associated with the Centaurus constellation. Its radiant point is located close to the star Omicron Centaurus, thus the name. Its activity period is from January 31 to February 19, peaking on February 11.
During the peak, the zenith hourly rate is 2. That means, we can expect to see two meteors an hour.
Theta Centaurids occur between January 23 to March 12, or as other sources say, from February 12 to February 16. It peaks on the 14th of February, with an hourly rate of 4. This fast meteor shower has a speed of about 60 km/s.
The radiant of Theta Centaurids lies west of the Lupus constellation.
Mythology Related to Centaurus Constellation
In Greek mythology, the centaurs have the upper body of a man and the lower body of a horse. They are often described as wild and savage beings who live in the mountainous parts of Thessaly. This is their origin:
The centaurs came to be when the king of the Lapiths, Ixion, tried to seduce Hera. Zeus knew about this and tricked him. The king of the gods made Nephele, a cloud that resembled Hera. Ixion was fooled and ended up with the cloud Nephele instead. From this, the centaurs were born.
Centaurus is said to be the sky representation of the centaur Chiron. Other sources say that it is Pholus, another centaur who is highly skilled in prophecy. Although Chiron is most commonly associated with it, no clear evidence as to who among the two is represented by the constellation. Their distinct characteristic of being wise and civilized, as opposed to the beastly and barbaric nature of most centaurs, made them great inspirations for Centaurus.
Chiron the Tutor
Chiron’s ancestry was different from other centaurs. His father was Cronus, the Titan king. He seduced a sea nymph named Philyra. To avoid being discovered by his wife, Rhea, he turned himself into a horse.
Later on, Philyra gave birth to Chiron. She was disgusted with her baby and abandoned it. The baby was found by no other than Apollo who became Chiron’s foster father. He taught the young centaur the arts such as medicine, music, and prophecy. Artemis, Apollo’s twin, taught Chiron archery as well as hunting.
Chiron was different from other centaurs not just in his manners but also in appearance. Unlike other centaurs, he is often depicted as having the front legs of a man. He also wore clothes that made him more cultured than the rest.
Chiron turned out to be highly respected in the fields of astrology, medicine, and prophecy among others. He became a teacher to many heroes including Achilles, Asclepius, Jason, Perseus, Ajax, and Aeneas.
Chiron and Achilles were in the cave of another wise centaur named Pholus when Heracles (Hercules) visited after one of his twelve labours. He drank the centaurs’ communal wine which made them very angry. The cave was attacked by the angry centaurs and a fight ensued.
Having no choice, Heracles had to fight back and shoot his arrows. They were poisoned with Hydra’s blood. Amid the commotion, one poisoned arrow hit Chiron.
Chiron was in agony but he cannot die because he was immortal. He bargained his immortality to free Prometheus who was chained to a rock for eternity. (In some tales, it was Heracles who rescued Prometheus). To honor Chiron’s noble act, his half-brother Zeus placed him in the sky.
In a different version, one story states that Chiron put his image in the sky to guide Jason and the Argonauts in their search for the Golden Fleece.
Changes in Centaurus Constellation
Centaurus was an equatorial constellation a long time ago. Nowadays, it is already in the southern sky as a result of precession.
The constellations of Circinus, Lupus, and Crux were previously part of Centaurus. Circinus was just an undefined area of the sky under the front hooves of the celestial centaur. It was later named and identified by Nicolas-Louis de Lacaille. Lupus, before it became known as a wolf, was an asterism of an unknown animal.
Another asterism that became a constellation of its own is the Crux. Before that, the Southern Cross was located on one of the hind legs of Centaurus. This may have been the place where Chiron was hit by the arrow that eventually led to his death.