The southern constellation Centaurus is massive, at over a thousand square degrees it's the ninth-largest overall. It is bordered by Hydra, Antlia, Vela, Carina, Crux, Musca (either side of Crux), Circinus and Lupus. It's well-known for containing the red dwarf star Proxima Centauri, the nearest star to our Solar System.

Mythology

Centaurs are mythical creatures which are depicted as (top) half man, (back) half horse. In some of the stories about them, centaurs are fearsome monsters. The constellation Centaurus honours the immortal Chiron, the offspring of the Titan Cronos (Saturn) and the nymph Philyra. While they were together, Cronos' wife caught the lovers in flagranté delicto so Cronos changed himself into a stallion in order that his wife would not recognise him. When Cronos the stallion ejaculated, he inseminated Philyra with equine semen and she conceived a demigod hybrid child. After Philyra gave birth to a half-equine son, Chiron, she was too ashamed to continue her old life, so she begged Zeus, the king of the gods, to alter her form. He acquiesced and changed the nymph into a linden tree.

Most centaurs were wild and uncouth but Chiron was a kind and wise teacher who counted the Greek hero Achilles, Jason, the leader of the Argonauts, and demigod Hercules among his pupils. Also a gifted and natural healer, Chiron taught Asclepius, who was the ancient god of healing and medicine, who has his own constellation, that of Ophiuchus the 'serpent-bearer'.

When a war broke out between the Greeks and the centaurs, gentle Chiron took no part. Hercules dipped his arrows in the blood of the Hydra to make them more effective against the centaurs. When Hercules accidentally injured Chiron with a stray poisoned arrow, he pleaded with the great god Zeus to end his suffering. Zeus took pity on Chiron and placed his image among the stars.

Stars

The scientific star names are simple to understand (if you know your Greek alphabet). For example: 'Alpha' means that it is the brightest star in that constellation. The next brightest is designated 'beta', etc. Some stars have proper names as well; for example, alpha Centauri is Rigil Kent; others are known by their catalogue numbers or 'Bayer designation'.

Stars of Centaurus

Alpha Centauri is a triple star system and the nearest star system to us, at just over 4.3 light years distance. The three stars are catalogued Alpha Centauri A, B and C — Alpha Centauri C is better known as Proxima² Centauri. This 12th magnitude red dwarf star is just 4.2 light years away, making it the closest star to our Sun.

New General Catalogue (NGC)

The NGC catalogue was compiled by John Louis Emil Dreyer (the director of the Armagh Observatory from 1882 to 1916). The constellation Centaurus contains several interesting deep-space objects, notably
Centaurus A (an elliptical galaxy), an edge-on spiral galaxy, a planetary nebula and many open clusters including the fabulous
Pearl Cluster. Of the two globular clusters, one, NGC 5139, is interesting for the fact that it was originally designated omega Centauri (catalogued as a star). It was only the second globular cluster discovered then, and it actually contains millions of stars packed tightly together. It's possible it was originally a dwarf galaxy which has been partially absorbed by the Milky Way.

Black Hole

Black holes, the beloved staple of science-fiction writers, are the most destructive things imaginable. They are collapsed stars that are so condensed that nothing, not even light, can escape their gravitational pull. Basically they're gravity gone mad, and anything that ventures close enough to get caught in their death grip gets stretched to obliteration. This isn't a companion you'd want in your intergalactic backyard, because it's a hungry monster which will never be sated. Although they were thought to be invisible and therefore undetectable, it's possible to see a black hole 'feeding' - we'd see a stream of matter under transference, a snapshot in deadly slow-motion. The edge-on spiral galaxy NGC 4945
has a suspected black hole at its core.

Boomerang Nebula

A fabulous protoplanetary nebula is a recent discovery therefore it doesn't have an NGC designation. It's been given the name Boomerang Nebula and is so beautiful that it made Astronomy Picture of the Day on 28 December, 2007. Another given name is the Bow-tie Nebula.

Extrasolar Planets

The Holy Grail of astronomers is to find the right size (rocky) planet orbiting its parent star at the correct distance for life to be viable and sustainable. The orbit would need to be non-eccentric, and the parent star should be stable. This 'just right' set of circumstances has earned the nickname the 'Goldilocks zone' after the children's story Goldilocks and the Three Bears. As of December 2007, no such planets have been found.

Methods used for detection have greatly expanded since the 1990s, and the techniques are being fine-tuned so Earth-like planets can be discovered and studied. Some methods include:

• The 'Wobble' technique: the planet's gravitational pull on its parent star produces changes in the star's light spectrum.
• MOA: Microlensing Observations in Astrophysics is a Japan/New Zealand collaboration using the gravitational microlensing technique at the Mt John Observatory in New Zealand.
• OGLE: Optical Gravitational Lensing Experiment makes observations at the Las Campanas Observatory, Chile, using a second generation CCD 8kMOSAIC camera. OGLE regularly monitors 130 million stars in the galactic bulge of the Milky Way.
• RoboNet: Optimised robotic monitoring of galactic microlens events at a UK national facility, the two metre robotic telescope at the Telescope Management Centre at Liverpool JMU (John Moores University). Although mainly concerned with delivering school-age educational programmes, the technique is being utilised to assist in the search for rocky Earth-like extrasolar planets.
  

Extrasolar Planets in Centaurus

The constellation Centaurus is rich in extrasolar planetary systems, the first was discovered in 2003. 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 size of the extrasolar planet is compared to the mass of Jupiter, our Solar System's largest planet, known by astronomers as the 'Jovian scale'.

Planet Chiron

The tiny planet which was discovered in 1977 in the outer region of the Solar System was named Chiron after the wise, kind teacher, and his long-forgotten story was rediscovered.

Galaxy Shape

Galaxies come in many sizes and shapes, usually spiral, elliptical, lenticular (a mix of the first two) and irregulars. In 2007 a project called Galaxy Zoo was set up for amateurs to help analyse galaxy images on their own home computers. Some of the images viewed would remind the 'zooite' of something, including this one of a centaur.

Down to Earth

Centaurs in Popular Culture

Centaurs are celebrated in art through paintings and sculpture. Sagittarius the archer is depicted as being a centaur carrying a bow and arrows. The image of a half-man half-horse creature appears in many cinematic guises, including Walt Disney's Fantasia; Xena, Warrior Princess; The Lion, The Witch and the Wardrobe by CS Lewis and the 'Harry Potter' stories by JK Rowling.

NASA used upper stage rockets, one of which was named Centaur, to launch deep-space probes and heavy satellites from 1958 and the two Voyager probes in 1977.

The great bard William Shakespeare had a fascination with the idea of the half-man half-horse creature the centaur. He wrote in Hamlet that Claudius describes a 'gentleman of Normandy' whose horsemanship seemed 'like witchcraft':

Such was the man's skill that he 'grew into his seat, and to such wondrous doing brought his horse as had he been incorpsed and demi-natured with the brave beast'.

And Finally ...

Centaur walks into a pub and the barman says: 'Why the short face?'