Centaurus
Written by Tammy Plotner
Centaurus is one of the largest constellations in the night sky – covering over 1000 square degrees – and the brightest in the southern hemisphere. It is also one of Ptolemy's original 48 constellations and is included in the 88 modern constellations. Centaurus contains 11 main stars, 9 bright stars and 69 stars with Bayer/Flamsteed designations. It is bordered by Antlia, Carina, Circinus, Crux, Hydra, Libra, Lupus, Musca and Vela. For observers located at latitudes between +30° and ?90°, the entire constellation is visible and the northern portion of the constellation can be spotted easily from the northern hemisphere during the month of May.
In mythology, Centaurus represents Chiron the Centaur – the wise half-man, half-horse who was a teacher to both Hercules and Jason. It is believed that the constellation of Sagitta is the arrow which Chiron fired towards Aquila the Eagle to release the tortured Prometheus. The nearby constellation of Lupus the Wolf may also signify an offering of Hercules to Chiron – whom he accidentally poisoned. Just as Virgo above represents the maid placed in the sky as a sign of pity for the Centaur's plight.
For the unaided southern skies observer, the constellation of Centaurus holds a gem within its grasp – Omega Centauri. NGC 5139 isn't a star – despite being listed on the catalogs as Omega. It's a globular cluster… the biggest and brightest of its kind known to the Milky Way Galaxy. How did it get to be known as a star when it isn't? Probably because that's the way Ptolemy wrote it down more than 2000 years ago. In 1677 Edmund Halley figured out it was a little something more, but he thought it was a nebula. Lacaille included it in his catalog as number I.5. Finally, in 1830, John Herschel recognized it for what it was – a huge ball of stars! Now have a look in a telescope or binoculars. This 18,300 light-year beauty contains literally millions of stars with a density so great at its center the stars are less than 0.1 light year apart. It is possible Omega Centauri may be the remains of a galaxy cannibalized by our own. Even to this present day, something continues to pull at NGC 5139's stars… tidal force? Or an unseen black hole?
Now, hop down to Alpha. Known as Rigil Kentaurus, Rigil Kent, or Toliman, is the third brightest star in the entire night sky and the closest star system to our own solar system. To the unaided eye it appears a single star, but it's actually a binary star system. Alpha Centauri A and Alpha Centauri B are the individual stars and a distant, fainter companion is called Proxima Centauri – a red dwarf that is the nearest known star to the Sun. Oddly enough, Proxima Centauri is also a visual double, which is assumed to be associated with Centaurus AB pair. Resolution of the binary star Alpha Cen AB is too close to be seen by the naked eye, as the angular separation varies between 2 and 22 arc seconds, but during most of the orbital period, both are easily resolved in binoculars or small telescopes.
More? Then at least stop for a moment to take a look at Beta Centauri. Known as Hadar or Agena, it's also one of the brightest stars on the night, coming in at number 10. Beta Centauri is well-known in the Southern Hemisphere as the inner of the two "Pointers" to the Southern Cross. A line made from the other pointer, Alpha Centauri, through Beta Centauri leads to within a few degrees of Gacrux, the star at the top of the cross. Using Gacrux, a navigator can draw a line with Acrux to effectively determine south. But, that's not all… Hadar is also a very nice double star, too. The blue-white giant star primary is also a spectroscopic binary, accompanied by a widely spaced companion separated from the primary by 1.3". Or try Gamma Centauri! Muhlifain has an optical companion nearby, but check it out in the telescope… it's really two spectral type A0 stars each of apparent magnitude +2.9!
For binoculars or telescopes, hop on over to NGC 5128 – better known as Centaurus A. This incredible radio source galaxy is one of the closest to Earth and also the fifth brightest in the sky. When seen through an average telescope, this galaxy looks like a lenticular or elliptical galaxy with a superimposed dust lane, and oddity first noted in 1847 by John Herschel. The galaxy's strange morphology is generally recognized as the result of a merger between two smaller galaxies and photographs reveal a jet of material streaming from the galactic core. Although we cannot see it, there may be a supermassive black hole at the center of the galaxy is responsible for emissions in the X-ray and radio wavelengths!
For binoculars and rich field telescopes, head towards the Crux border and center on Lambda Centauri for open cluster, IC2944. Also known on some observing lists as Caldwell 100, this scattered star cluster contains about 30 stellar members and some faint nebulosity. About 2 degrees southwest of Beta you'll find another pair of open clusters, NGCs 5281 and 5316. Or try your hand just about a degree west of Alpha for open cluster, NGC5617. These last three are far more rich in stars and photon satisfying!
Constellation Chart Provided by Your Sky.
Filed under: Astronomy
