Omega Cen's millions of stars

By Phil Plait | December 2, 2008 10:00 am

I love it when astronomers release beautiful images simply because they are beautiful.

That’s Omega Centauri, a globular cluster. It contains millions of stars, all gravitationally bound to one another. It orbits the Milky Way and is currently about 18,000 light years away. At 150 light years across, it’s a densely packed beehive of stars.

It’s also easily visible to the unaided eye. Centaurus is a southern constellation, so it’s high overhead if you live south of the Equator. But many years ago, while I was doing my Master’s research at the University of Virginia, I saw it with my own eyes. I was out on the telescope catwalk that circled the dome, and was just looking at the stars. Right on the horizon, nestled between two Smoky Mountain peaks, was a fuzzy dot. I watched it for a few minutes, puzzling over what it could be. A cloud? No, it wasn’t moving. Smoke from a chimney? Maybe, but in the summer?

Then it hit me. Omega Cen? No, couldn’t be! But I went inside and checked the cluster’s coordinates. Knowing my latitude, I did the numbers in my head and realized that Omega Cen could just barely be seen, given the conditions: I was up high, looking between two mountains, and atmospheric refraction (the bending of light from stars upward due to the Earth’s air) near the horizon would lend a hand as well. I checked through binoculars, but the thick air only made the fuzzy dot a little bigger.

Still, that was an amazing moment for me; I had no idea you could see Omega Cen that far north. Of course, when you observe it from Chile with a 2.2 meter ‘scope, you get a slightly better view, as shown above.

And let me repeat: the European Southern Observatory didn’t release this image to go with any big scientific result. It was just simply a gorgeous image, and they wanted to share. Awesome.

Image courtesy ESO.

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (34)

  1. I want to try seeing this from Fan Mountain too. Maybe next summer…
    Gotta love me some globs!

  2. kuhnigget

    Dr. BA:

    I have always felt scientists should make a greater effort to involve the public in the sheer wonder of the universe. Thanks for this, and to the ESO astronomers. This is magnificent.

  3. Very nice! So, would it be visible from sea level if I was on a boat in the Gulf of Mexico, off the coast of (for instance) Mobile, AL.?

  4. Kapella

    I saw it from the Kenton, Ohio airport many years ago, while searching for Halley’s comet.
    Here’s the airport info:
    FAA Identifier: I95
    Lat/Long: 40-36-38.5920N / 083-38-36.9490W
    40-36.643200N / 083-38.615817W
    40.6107200 / -83.6435969
    Elevation: 1024 ft. / 312.1 m (surveyed)

    It was a bubbly ball of unresolved stars, barely 3 degrees above the horizon.

    I have also seen it from Puerto Rico….magnificent!


  5. Craig

    Regarding the density of the cluster; is it at all possible that there could be planetary systems within the cluster?

    If so, and you were standing on a planet looking up at the sky, what would it be like? Would there be no day or night?

    When talking about star clusters, what constitutes “density”? Is this an environment where it’s like a country club with a star-only membership?

    I wish this blog had a thread once in a while to ask stuff. It seems that there are a great many knowledgeable people here, in adition to Dr. Plait.

    “Enquiring minds want to know”.

  6. I was recently speaking to an amateur group and said that Omega Cen could not be seen from Texas. They assured me that it could definitely be observed — just barely coming over the horizon when it crosse the meridian.

    BTW, Phil. Omega Cen is probably a dwarf galaxy that has merged with the Milky Way.

  7. Wendy

    What an amazing image!!! It’s shots like this that make me wish intergalactic travel was an everyday thing. 😀

  8. Metre

    Looks like a spoonful of sugar spilled onto a black table cloth. Sweet!

  9. Amazing picture. I remember the first time I saw the Wild Duck Cluster, through my 3.5″ Mak/Cass., and the sense of wonder.

  10. Dave

    This is an amazing photo. Kudos to the ESO team.

    I first saw Omega Cent. on my honeymoon. My wife and I took a western Caribbean cruise. I made sure to find the darkest spot I could (not easy on a cruise ship) one night when we were well south of Jamaica.

    Omega Cent. was a naked eye smudge in the night sky, and clearly a glob in 10×50 binoculars. Between that and seeing Alpha Cent. for the first time that night I was in heaven. Words fail to describe my sense of wonder at the time. Awesome is the only word I have to describe it; and it fails to capture the enormity of it.

    This is why I love astronomy. I just wish I could fully convey that sense of awe that the universe inspires in me. I can’t, but I try to do my best.

  11. justcorbly

    When I look at images like this, I always stars at an immense distance and I know that many of those stars have planets and that, just maybe, someone on some of those planets is looking back at me.

    There’s grandeur and awe and reverence going on, and I’m sure it’s the same for the rest of you.

    I wonder, though, if some people see nothing more than a pretty little picture, even when they know what the image shows. I can’t comprehend how anyone could look at images like this and not be impressed to be part of the universe, but I’m sure some folks just don’t the jump for “bunch of tiny dots” to “They’re stars!”

  12. Far beyond this world I’ve known, far beyond my time…
    (Buck Rogers closing credits).

  13. If you start at the center of the photo, and start looking towards the right side of the image, you’ll see a fairly bright white/blue star (?) that’s slightly lower than the vertical center of the photo … Just above that, and just barely slightly left is a tiny smudge … If you zoom on that exact area you’ll see two smudgy objects … What are those?

    It looks like they’re much closer than everything else in the photo (almost like everything else is a 2D backdrop). They look a bit rock-like, so I’m wondering if they’re asteroids or bits on the ‘scope.

  14. …replying to myself here….
    I just noticed that they’re perfectly square, so they must just be fragments of the image that just didn’t “take”

  15. American Voyager

    Incredible image! I’ve always loved this one. Mike mentioned above that it might be a dwarf galaxy. I heard that once too – that it is another satellite galaxy because of its size. Is there any other difference between a globular and a dwarf galaxy? Either way, it’s gorgeous!

  16. Regarding the possibility of planets, Omega Centauri was surveyed for transiting planets but none were found. The environment is very low metallicity, so (according to current planet formation theories) it’s unlikely that planets have formed there. Then again, in the globular cluster M4, again a very metal-poor environment, there appears to be an object with a few times Jupiter’s mass orbiting the neutron star+white dwarf binary PSR B1620-26. And it’s anyone’s guess whether there are planets in the few known metal-rich globular clusters, e.g. Terzan 5, Liller 1, which are somewhat difficult to observe because they are highly obscured by material in our own galaxy.

  17. Tom


    I just ran some quick calculations, and Omega Centauri would have an apparent magnitude of -6.3 at a distance of 170 light years (i.e. right next to it). At that distance, it would cover about 60 degrees of sky and would be a few times brighter than Venus is from Earth.

    So, you wouldn’t be able to read a newspaper under the night sky, but you might be able to see enough to walk around once your eyes adapted to the ‘darkness’.

  18. Phil, your personal “discovery” of Omega Cen reminds me of when I “discovered” the Milky Way. I was driving in the Arizona desert late one night and I kept seeing what I interpreted as a cloud. It eventually dawned on me that there weren’t any clouds in the sky at all. I was seeing the Milky Way for the first time in my life.

    It is a kind of a weird thing to say, though. It is like growing up somewhere and never looking at your house until you are grown up. So this is where I live! Hmm. Fascinating. Never noticed it before.

  19. Jimbalaya, it’s almost certainly an image processing defect. A lot of work goes into processing the images to make them pretty, and even to make them scientifically useful. Calibration images alone outnumber the actual image of stars usually 4 or 5 to 1! So it’s probably something like cosmic rays being removed, or a problem with the detector, and they did their best to fix it.

  20. Jimbalaya, the Wide Field Imager, the CCD camera used to capture the data for this image, is a mosaic of 8 chips, and there are gaps between the chips. Astronomers usually try to fill these gaps capturing different exposures of the same object, but sometimes they cannot fill the gaps perfectly, or they don’t need to fill them (these data were not collected for imaging purpose). We filled the gaps using bits from the Digitized Sky Survey, but this is far less good than the rest of the image. That’s why over the image there are few “blurred” and slightly differently coloured areas.

  21. ad

    Thanks, ESO Press Officer: Dr. Henri Boffin.

  22. PJE

    I was in Australia in July and had my first look through a real telescope at the Ayer’s Rock resort (Uluru). I had a chance to see two globular clusters at about 10 pm or so.

    Would this have been one of them? THey were both remarkable but I don’t remember any names


  23. JB of Brisbane

    Peter Payne beat me to it.

  24. What’s really stunning about this picture release is the size of the image files ESO offers on its server: You can have your own Omega Cen with 65 Megapixels and 140 MB! And then do what with it?

    Hint: The fulldome projector with the highest resolution on the market today (in use only at Beijing’s planetarium so far but made in the U.S.) throws 35 megapixels onto the ceiling. It would be fun to feed the Omega Cen picture into this system …

  25. Radwaste

    Time for a little pop-psych. We know what makes a man handsome and a woman beautiful, why green grass is nice and so forth – but why are some of us so pleased by celestial objects?

  26. jess tauber

    I keep noticing structure in shots of globulars- it looks like looping streamers of stars, many oriented the same way. One might expect an optical illusion in the mind’s wish to make order out of randomness, but then one DOES see such order in many open star clusters- why not in globulars?

  27. Ijon Tichy

    PJE, there’s a good chance you were looking at Omega Centauri. There’s also a good chance that the other one was 47 Tucanae (NGC 104). Those are the top two monster globulars in the southern hemisphere. But there’s quite a few other spectacular examples like M22 in Sagittarius, NGC 6397 in Ara, and NGC 6752 in Pavo.

  28. llewelly


    It’s those damn aliens in their UFOs. Always abducting us and screwing with our gene pool. It’s alien genes that make us long for the stars.

  29. Mark Hansen

    I remember the first time I saw Omega Cent through a telescope. At very low magnification it looked like a smudge of talcum powder on black velvet. Then the higher magnification and “Oh wow!”

  30. TheWalruss

    I lived for a year on a lake in the middle of nowhere. Every night and every morning I’d go out and just look around. Sometimes it would be the clouds, or snow, or ice crystals, or rabbits, or trees, or reeds shifting in the wind that would create that aesthetic tingle I was looking for.

    But by far the most powerful was the clear sky – the Milky Way spinning overhead bold and bright. I would stare straight up for what seemed like hours, mouth agape, until my girlfriend got annoyed or afraid I’d get frostbite or die of hypothermia and call me inside.

    Imagine the view from within that cluster!

  31. Nigel Depledge
  32. kuhnigget

    @ Tom ‘n’ Craig ‘n’ Walruss:

    For an interesting take on what it would be like to live on a planet within a globular cluster, read Isaac Asimov’s classic story, Nightfall.

    It chronicles a civilization on a world orbiting within a multiple-star system, which is in turn located in the heart of a globular. Because of their multiple suns, their “night” only falls once every two thousand years when all of their suns are eclipsed by moons. Unfortunately….heh heh…read the story.

  33. TheWalruss

    Oh yea! I read that story way back in middle school!

    Good call, Kuhnigget!

  34. Mark Hansen

    Perhaps this was inside the monolith that Dave Bowman entered…


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