How to see it
From our northern temperate latitudes, Omega Centauri – the Milky Way galaxy’s largest and most luminous globular star cluster – can only be seen at certain times of the year. Omega Centauri is best seen from the northern hemisphere on May and early June evenings. Around middle May, this wondrous star cluster is due south and highest in the sky around 10:00 p.m. (11:00 p.m. daylight saving time). By mid-June, Omega Centauri is highest up (and due south) around 9:00 p.m. (10:00 p.m. DST). Northern hemisphere residents can see Omega Centauri from January through April as well, but they must be willing to stay up past midnight or to get up before dawn.
Omega Centauri is visible from the southern half of the United States, or south of 40 degrees north latitude (the latitude of Denver, CO). Canadians hasten to remind us, though, that they can actually spot Omega Centauri from as far north as Point Pelee in Canada (42 degrees latitude). When seeing conditions are just right, they can catch the Omega Cenaturi star cluster skimming along the surface of Lake Erie.
Spica, the brightest star in the constellation Virgo, serves as your guide star to Omega Centauri. When Spica and Omega Centauri transit – appear due south and reach the highest point in the sky – they do so in unison. However, Omega Centauri transits about 35 degrees south of (or below) sparkling blue-white Spica. For reference, your fist at an arm length approximates 10 degrees of sky. Find Spica’s transit time for your sky at this UN Naval Observatory page.
Omega Centauri is a globular cluster
Omega Centauri is a globular star cluster. This disguishes Omega Centauri from clusters such as the Pleiades and Hyades, which are open star clusters. An open star cluster is a loose gathering of dozens to hundreds of young stars within the disk of the Milky Way galaxy. Open clusters are weakly held together by gravity, and tend to disperse after several hundreds of millions of years. Globular clusters orbit the Milky Way outside the galactic disk, and harbor tens of thousands to millions of stars. Tightly bound by gravity, globular clusters remain intact after 12 billion years.
Generally, open clusters visible to the unaided eye are hundreds to a few thousand light-years away. In contrast, globular clusters are generally tens of thousands of light-years distant. At 17,000 to 18,000 light-years, Omega Centauri is one of the few of the galaxy’s 200 or so globular clusters that is visible to the unaided eye. It looks like a faint, fuzzy star, but Omega Centauri’s mere presence testifies to its size and brilliance. Like any globular cluster, Omega Centauri is best appreciated with a telescope.
No ordinary globular
All globular clusters are impressive, but Omega Centauri is in a class by itself. Having a mass of 5 million suns, Omega Centauri is 10 times more massive than a typical globular cluster. Omega Centauri sports a diameter of 230 light-years, this bejewelled stellar city sparkling with perhaps 10 million stars.
Globular clusters generally have stars of similar age and composition. However, studies of Omega Centauri reveal that this cluster has different stellar populations that formed at varying periods of time. It may be that Omega Centauri is a remnant of a small galaxy that merged with the Milky Way.
Omega Centauri’s position is at Right Ascension: 13h 26.8m; Declination: 47 degrees 29′ south
As a south american dweller(Brazil),I´m gifted by this cosmic jewel high in the sky in his season (to us,winter)
Thankyou for so much useful informations of easy understand!!!
”high in the sky in this season…”lol
What a write!! Very informative also easy to understand. Looking for more such blogposts!! Do you have a myspace?
I recommended it on stumbleupon. The only thing that it’s missing is a bit of speed, the pictures are appearing slowly. However thank you for this information.
[...] in this sharp telescopic image, globular star cluster Omega Centauri (NGC 5139) is some 15,000 light-years [...]
I wonder how close these stars are to each other. I would think at any given point within the cluster if you lived on a planet there you could see many many suns in the sky at once. Probably never getting dark there.
At best we may have just a few thousand stars in the same space as the millions in the Omega Cen cluster. Wow!
I was wondering too, so I will indulge myself. As a very rough estimate:
1) Calculate the volume of the cluster
2) Divide that volume by the number of stars to get average volume allowed for each.
3) Calculate the radius of a sphere of that average volume.
4) Multiply the resulting radius by 2 to give a distance between centers.
The basic idea is that we put each star in a “little ball” such that the volume of all the “little balls” equals the volume of the cluster. Then calculate the distance between centers of all the little balls packed into the cluster.
I looked up sphere packing and learned that the theoretical limit for the volume of the packed spheres is about 0.74 of the total space available. So I adjusted by multiplying the volume of the cluster by (1 / 0.74). There is no way this is mathematically legitimate, but I had to do *something* :-)
[Perhaps someone that actually knows how to do this stuff could pitch in?]
km / light year 9.46E+12
r (cluster) 1.09E+15 km
adj volume 7.29+45 km**3
number of stars 1.00E+7
volume per star 7.29E+38 km**3
radius 2.27E+12 km
distance (ly) 4.54E-01
So an average distance of .45 light years between stars – let’s call it “less than half a light year”. And certainly closer nearer the center of the cluster. Close enough for starfaring civilizations to exist?
David,
I commend you for your efforts!! According to the information presented at http://www.astro.keele.ac.uk/workx/globulars/globulars.html: “The average star density in a globular cluster is about 0.45 stars per cubic parsec. In the dense center of the cluster, the star density can increase from 100 to 1000 per cubic parsec.”
Since one parsec = 3.26 light-years, I presume one cubic parsec is equal to about 35 cubic light-years (3.26 x 3.26 x 3.26 = <35)
Bruce
Thank you Bruce and David. Great article. Great info.
You’re welcome Ram
Seems this website doesnt load rightly with a Motorola Citrus. Are some other folks getting the exact same difficulty ?
Very interesting and readible article. Thank you. I am South African and used to observation in the southern Hemisphere. Amateur astronomers ussually have specific celestial sights that made the biggest first impression (excluding the planets, they are ussually the orion nebula, carinae nebula, andromeda galaxy, the jewel box etc.). For me personally it was the Omega Centauri Cluster that made the biggest impression on me. When viewed through a telescope the stars in the cluster sometimes creates the illusion to the eye that they are moving at high speed towards the observer. At times it appears almost “unreal” as if it is an electronic image of some kind. Truly spectacular. The image in this article is excellent, however, Omega Centauri is one of those sights that one simply has to observe first hand through a telescope to truly appreciate its wonders. We are lucky I suppose in the southern hemisphere to be able to view all the spectacular sights around Crux and Centauri throughout the year.