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CENTAURUS
The Centaur
Centaurus - Uranometria by Johann Bayer - 1603
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Centaurus is found in the southern sky, and isn't visible much above 25 degrees latitude, but it is one of the most important constellations in the sky, containing the closest star to Earth, as well as the brightest and most impressive globular cluster in the sky. The constellation represents the classic Centaur - half man, half horse - of mythology, named Chiron. According to legend he was wise and benevolent, and tutored Hercules, the son of Zeus (Jupiter). When Hercules accidentally shot and killed Chiron with a poisoned arrow, he asked Zeus to immortalise his beloved teacher by placing his image in the sky. Centaurus is seen straddling probably the most famous and most distinguishable constellation in the southern sky: Crux (the southern cross). Chiron carries a spear, with which he threatens the wolf, Lupus, placed in the sky beside him.
The constellation of Centaurus has the important distinction of containing the closest star to Earth: Proxima Centauri. Although it is closer than any other star, Proxima Centauri is still a staggering 4.21 light years away, about 25 trillion miles. The fastest possible twenty-first century technology would still take tens of thousands of years to reach it.
Proxima Centauri is an M5 red dwarf, only one seventh the size of our Sun. With an apparent magnitude of 11.05, it is well out of range of naked eye visibility. Because it is so close to the binary system of Alpha Centauri, most scientists agree it must be in some way gravitationally bound to them, although this has not been officially confirmed.
Slightly further away, at a distance of 4.37 light years, Alpha Centauri is the third brightest star in the sky. With an apparent magnitude of -0.27, only Sirius and Canopus are brighter. Appearing as one bright star to the naked eye, Alpha Centauri is actually a binary system, consisting of Alpha Centauri A, and Alpha Centauri B. As mentioned above, if Proxima Centauri is in fact a gravitational partner of these two stars, it would make Alpha Centauri a triple star system. Alpha Centauri is also known as Rigel Kentaurus, the foot of the Centaur.
As well as containing the closest star to Earth, Centaurus also harbors the brightest globular cluster in the entire sky: NGC 5139. With an apparent magnitude of 3.9, it was considered a star throughout most of history, and given the designation of a star, Omega Centauri, by which it is referred to this day. It wasn't until 1830 when English astronomer John Herschel first identified it as a globular star cluster. It is 15,800 light years away, and contains tens of millions of stars, very much more than any of the 150 other globular clusters that surround our galaxy.
With an apparent magnitude of 6.8, NGC 5128 is the fifth brightest galaxy in the sky, making it a favourite target for small telescopes. Also known as Centaurus A, or Caldwell 77, it is 15 million light years away. NGC 5128 is a powerful source of X-rays, produced by a supermassive black hole at its centre.
NGC 4945 is a large spiral galaxy very similar to our own Milky Way galaxy. It is 13 million light years away, with an apparent magnitude of 9.2.
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