Omega Cen's millions of stars

The entire universe in blog form
Dec. 2 2008 10:00 AM

Omega Cen's millions of stars

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


Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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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.

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