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OzSky Star Safari - Southern Skies Showcase:
Omega Centauri

Omega Centauri (NGC 5139, Caldwell 80) Omega Centauri - Credit: ESO
Image Credit: ESO

R.A: 13h 27' 49"
Dec: -47 34' 01"
Mag: +3.68
Const: Centaurus (Cen)
Best at: OzSky "Classic" Star Safari in April

Omega Centauri is a spectacular globular cluster in the southern constellation of Centaurus (Cen). Omega Centauri is one of the first targets of many observers at The OzSky Star Safari, transiting the April meridian around midnight at an impressive altitude of around 74 above the horizon.

Shining at a magnitude of +3.68, it is one of the few globular clusters easily visible to the naked eye.

Located approximately 17,000 light-years (5.2 kpc) away, and with a diameter of about 271.3 light years (83.2 pc), it is the largest globular cluster in the Milky Way.

Omega Centauri is estimated to contain approximately 10 million stars and has a total mass equivalent to 4 million solar masses making it the most massive known globular cluster associated with the Milky Way and the second-most massive of all Globular Clusters in the entire Local Group of galaxies - Only Mayall II (NGC-224-G1, SKHB 1, GSC 2788:2139, HBK 0-1, M31GC J003247+393440 or Andromeda's Cluster) in the Andromeda Galaxy is more massive.

Orbiting through the Milky Way, Omega Centauri contains several million Population II stars and is about 12 billion years old. The stars in the core of Omega Centauri are so crowded that they are estimated to average only 0.1 light years away from each other.

It has been speculated that Omega Centauri may be the core of a dwarf galaxy that was disrupted and absorbed by the Milky Way. Indeed, Kapteyn's Star, which is currently only 13 light years away, is thought to originate from Omega Centauri. Omega Centauri's chemistry and motion in the Milky Way are also consistent with this picture. Like Mayall II, Omega Centauri has a range of metallicities and stellar ages that suggests that it did not all form at once (as globular clusters are thought to form) and may in fact be the remainder of the core of a smaller galaxy long since incorporated into the Milky Way.

In 150 A.D., Ptolemy catalogued this object in his Almagest as a star on the horse's back, "Quae est in principio scapulae". Johann Bayer used Ptolemy's data to designate this object "Omega Centauri" with his 1603 publication of Uranometria. Using a telescope from the South Atlantic island of Saint Helena, Edmond Halley rediscovered this object in 1677, listing it as a non-stellar object. In 1715, it was published by Halley among his list of six "luminous spots or patches" in the Philosophical Transactions of the Royal Society.

Swiss astronomer Jean-Philippe de Cheseaux included Omega Centauri in his 1746 list of 21 nebulae,[13] as did French astronomer Lacaille in 1755, who gave it the catalogue number L I.5. It was first recognized as a globular cluster by Scottish astronomer James Dunlop in 1826, who described it as a "beautiful globe of stars very gradually and moderately compressed to the centre"

References: SkySafari 5 Pro (iPhone app); Wikipedia

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