Star Constellation Facts: Centaurus

Star Constellation Facts: Centaurus

Centaurus is the ninth largest constellation, and takes up an area of 1,060 square degrees of the southern hemisphere night sky, although it can be seen by any observer located between latitudes +25° and -90°. Centaurus is home to two of the top ten most luminous stars in the sky, namely Alpha Centauri, and Beta Centauri, in addition to one of the most active galaxies known called Centaurus A.

In addition, Centaurus contains Omega Centauri, one of the Milky Way’s largest attendant globular clusters. This cluster, that is estimated to have about 1 million solar masses, is a perennial favourite among southern observers, and once seen through a telescope, it is never forgotten. Although Centaurus contains no Messier objects, it does have eleven stars with confirmed planets, and several notable deep sky objects, such as the Southerner, a famous blue planetary nebula, and the equally famous Boomerang Nebula.

Hercules Family of Constellations

Centaurus belongs to the large Hercules family of constellations, which includes the constellations Aquila, Ara, Centaurus, Corona Australis, Corvus, Crux, Crater, Cygnus, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Scutum, Serpens, Sextans, Sagitta, Triangulum Australe, and Vulpecula.


The origins of the constellation can be traced back all the way to ancient Babylon, when it was known as “the Bison Man” and associated with Shamash, the sun-god. In ancient Greece and Rome, the constellation was linked to a race of half-human, half-horse creatures known as centaurs. The constellation is thought to depict the noble centaur called Chiron, a wise, high-born creature that mentored many famous heroes in the study of music, medicine, and hunting, including Jason, Theseus, and Heracles. Unfortunately, Heracles accidentally shot the centaur with a poisoned arrow but since he was immortal, Chiron could not die from the deadly poison. Instead, he suffered terrible agony until Cronus turned his son into a mere moral, thus allowing him to die before placing him in the sky. The Centaurus constellation depicts a mythological scene involving three constellations, with Chiron (Centaurus) impaling a wolf (Lupus) on his spear in order to sacrifice it on an altar (Ara) for the gods.

Notable Stars

– Rigil Kentaurus (Alpha Centauri) is our closest stellar neighbour, and is a triple star system, with the most luminous component Alpha Centauri A, being a G2V-class mainsequence star that’s about 10% more massive than the Sun. Alpha Centauri B on the other hand, is a K1V-class main sequence star, and slightly smaller than the Sun. Although

Star Constellation Facts: Centaurus

it is exceptionally bright with an apparent magnitude of 1.33, it ranks at number 21 in the sky in terms of brightness, making it marginally more luminous than the star Regulus in the constellation Leo. Alpha Centauri and Beta Centauri are believed to be roughly the same age at about 4.85 billion years, making them around 450 million years older than the Sun.

– Proxima Centauri (Alpha Centauri C) is the third star in the Alpha Centauri system, and is a red dwarf located 2.2 degrees away from the Alpha Centauri AB pairing, and thought to be gravitationally bound to the bigger stars. Proxima Centauri is either a M5Ve or M5Vie-class star, meaning that it could be either a small main sequence star, or perhaps a sub-dwarf. Nevertheless, it only about 12% as massive as the Sun, and it is expected to spend at least four trillion years on the main sequence.

– Hadar (Agena, Beta Centauri) is a giant, blue-white B1III-class star 349 light years distant, and with with an apparent magnitude of 0.6, making it the tenth most luminous star in the entire sky. Hadar is actually a multi-star system with the primary component, Hadar A, being a spectroscopic binary system with both stars being identical, and having an orbital period of 357 days. At least one of the components is a Beta Cephei variable star. The companion star in the system, Hadar B, is located 1.3 seconds of arc (210 AU) from the primary pair, and takes about 600 years to complete one orbit.

Notable Deep Sky Objects

Centaurus A (NGC 5128) is not only the closest radio source to the solar system, it is also the fifth most luminous galaxy in the entire sky with an apparent magnitude of 6.84, despite being located between 10 and 16 million light years away at the centre of the Centaurus A subgroup of the very big Centaurus A/ M83 Group of Galaxies. More than 100 active star forming regions have been identified within the galaxy, with most, if not all, being the result of an ongoing collision with a large spiral galaxy.

Omega Centauri (NGC 5139)Omega Centauri (NGC 5139) is located just four degrees to the southward of Centaurus A, and is the largest, and most massive of the globular clusters surrounding the Milky Way. It has an apparent magnitude of 3.7, making it bright enough to be spotted without optical aid, even at a distance of about 15,800 light years.The cluster is estimated to be about 12 billion years old. The origin and formation of Omega Centauri is not certain, but it is believed to be the remains of a dwarf galaxy that was tidally stripped by the Milky Way.

The Blue Planetary (NGC 3918)The Blue Planetary (NGC 3918) is a spectacularly beautiful planetary nebulais about 4,900 light years distant, and with an apparent magnitude of 8.5, making it the brightest planetary nebula in the southern skies. The nebula is approaching Earth at about 17 km/second, while it is expanding at around 24 km/second. Note that the central bright dot in the nebula is a foreground object and not the progenitor star, which is not visible to optical observers due to the sheer brightness of the nebula.

Meteor Showers

Alpha Centaurids; while this shower can be active during most of February, the peak usually occurs on the 6th/7th of the month. Observers in the southern hemisphere usually get a better view of the shower, although maximums rarely exceed 20 meteors per hour.

Omicron Centaurids; another weak shower, it is best viewed from the southern hemisphere from late January to early February, with the peak on February 14th. Best views of the shower is from around 2:00 AM local standard time, when between five and ten meteors per hour can be expected.

Theta Centaurids; this shower occurs from around January 23rd to March 12th, with a peak on February 14th. The shower is only visible from the southern hemisphere. Although meteors are usually fast at around 60 km/second, maximums of as few as 2-4 meteors per hour is the norm.

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