Centaurus

The space enclosed by the constellation Centaurus includes a part of the Galactic Nucleus and, beyond that, the long arc of the distant Sagittarius Arm.

A rich and extensive constellation of the southern sky. Centaurus contains much that is of interest, but is perhaps most famous for the stars Proxima and Alpha Centauri, the nearest stars to Earth's Solar System.

Centaurus in the Sky

The southern constellation of Centaurus lies to the south of the immense Water Snake of Hydra, but is perhaps most easily located through the Southern Cross, Crux, a small constellation that Centaurus surrounds on three of its four sides. (Indeed, the stars now known as Crux was at one time considered part of Centaurus).

The two brightest stars of Centaurus, Alpha Centauri and Hadar, are known as the Southern Pointers, and a line through those stars leads on towards Crux (and specifically the star Gacrux in that constellation). A line running perpendicularly between these two pointer stars leads the way towards the sky's southern pole.

Stars

At the eastern foot of the Centaur is one of the brightest stars in the sky, variously known as Rigil Kentaurus or Toliman, but most usually referred to by its Bayer designation of 'Alpha Centauri'. Though it appears as a single bright star in the sky, this is in fact a binary system, with two Sun-like stars in orbit around one another. Alpha Centauri is especially notable as being among of the closest stars to the Solar System, at a distance of just 4.4 light years. A little to the south of Alpha Centauri is a faint red dwarf star, Proxima Centauri. This is actually an outlying member of the Alpha Centauri system, and is the closest star to Earth (excluding the Sun) at just 4.2 light years.

A little to the west of Alpha Centauri is another bright star, known as Hadar or Agena, a blue giant that is more than a hundred times farther from the Solar System than its apparent neighbour Alpha Centauri, but so intrinsically luminous that it appears almost as bright in the night skies of Earth.

From Alpha Centauri and Hadar, an arc of stars surrounds little Crux to reach their end in Lambda Centauri, the western foot of the Centaur. Out of this arc a further group of stars reach out from the band of the Milky Way. The northernmost of these stars making up the body of the Centaur is Menkent or Theta Centauri, the third brightest of Centaurus' stars after Alpha Centauri and Hadar (or the fourth brightest, counting Alpha Centauri's component stars individually). The name Menkent appears to come from the Arabic for 'Shoulder of the Centaur'; this star is an orange giant some sixty light years from the Solar System.

Deep Sky Objects

Within the central regions of Centaurus lies an object bright enough to be clearly visible to the naked eye. When Bayer catalogued the stars of the constellation in 1603, he took it to be a star, and accordingly gave it the stellar designation Omega Centauri. Within a century it was recognised as something else entirely: a brilliant and extraordinary globular cluster, and in fact the brightest such object in the skies of Earth. (The only other cluster of this kind visible to the naked eye - 47 Tucanae - was also initially misclassified as a star.)

Within the western 'leg' formed by the Centaur's boundaries lies another object within our own Galaxy, at a distance approaching 6,000 light years: the Blue Planetary Nebula. This is a distinctive planetary nebula, though unlike Omega Centauri it is not visible without telescopic aid.

Centaurus several galaxies beyond the Milky Way, with two being particularly notable. More than ten million light years out into space lies the galaxy known as Centaurus A, a remarkable starburst galaxy with a central black hole ejecting immense jets of material perpendicular to the galaxy's plane. Far beyond Centaurus A - nearly 200 million light years from the Milky Way - is the complex of galaxies designated NGC 5291. Within this complex is the Seashell Galaxy, twisted by gravitational forces into a shape remarkably reminiscent of the seashell that gives it its name.