A bright globular cluster is a diamond brooch hanging against the black velvet dress of the heavens. Thousands of points of light are scattered on the outskirts, yet so dense in the middle that there they form a solid glittering encrustation.
The first time Deloy Pierce saw one through a telescope at a site away from light pollution, "it was absolutely amazing," he said."The sky was really black and there were just more stars than I could imagine." He said a description that seemed to fit was, "It's like sprinkles of sugar grains on black paper."
Globular clusters are among the loveliest views that can be seen through moderate-size amateur telescopes, and this is a good time to see two of the best:
- M13, a starburst 23 light-years away in the constellation Hercules. It has 100,000 stars packed within a diameter of 15 light-years. If you were to go to a star party on a clear night, you could see it almost directly overhead by 10 p.m. and heading westward as the night progressed. The higher an object is in the dark sky, the better to see it.
- M22, the brightest globular cluster visible this far north, with 70,000 stars. About 10,000 light-years away, it's one of the closest. You can find it in the constellation Sagittarius. Look in the southern sky in the midst of the stream of the Milky Way, just to the left of the top of the asterism called the "teapot."
These spherical clumps of stars formed early in the life of the universe. Astronomers date them at 12 billion to 16 billion years old. Their populations vary from 10,000 to more than a million stars.
They are called globular because they are globe-like, as opposed to open clusters of stars that are neither so condensed nor so old. (However, the word is pronounced "glob-ular," not "globe-ular.") Contrary to most things we can see, they are not in the plane of our galaxy. The 150 or so globular clusters orbit the Milky Way in a halo.
"They're very beautiful to look at," said Dave Chamberlin of the University of Utah Chemistry Department. "Their photographs aren't as nice-looking as they are in reality, when you look at them with a telescope.
"You're looking at thousands of dots of light, usually a faint bluish-green color. . . . Some of them are very impressive." With some, he noted, a watcher may be "seeing maybe 200,000 stars at once."
Why aren't they in the plane of our galaxy, instead of buzzing around it like bees around a hive? "Nobody knows for sure," Chamberlin said.
Globular clusters are among the first objects that can be resolved in other galaxies, he added. Galaxies are so far apart it's difficult to see individual stars even with big telescopes. Some galaxies have thousands of globular clusters, and many of the clumps are bright enough to distinguish.
In 1996, the Hubble Space Telescope photographed something called G1, a globular cluster orbiting the Andromeda galaxy. Since it was Hubble, this bright ball of 30,000 stars - located 1.5 million light years away - is as distinct as a view of one of our own galaxy's globulars, taken with a nice-size telescope on Earth. And it looks like a typical globular orbiting the Milky Way.
Scott Crosby, who has an observatory in Bountiful, is a big fan of a globular clusters. "I like to go after some of the globulars that aren't observed quite so often," he said.
Holly Phaneuf, who lectures in astronomy at a couple of Salt Lake colleges, traveled to Bonaire in the Caribbean last February with her husband, Hansen Planetarium spokesman Patrick Wiggins. They went to the island to watch the total solar eclipse, "but another reason that I was really excited to get down there is because I've never been so far south and I was hoping to see some of the southern constellations that I'd never seen before," Phaneuf said.
On the last night of their visit she tried to find omega Centauri, the biggest globular cluster of all. It has at least a million stars and is relatively close - 17,000 light-years away. Because it's so far south, you'd have to travel at least to Texas for a good view.
She read in an astronomy manual that the cluster is large and luminous enough to see with the naked eye. So she tried to spot it.
"I was looking in the right constellation but on the island it was just cloudy all the time, patches of cloud everywhere. And looking and looking for this thing just in the right area, but I kept seeing this little cloud right where it ought to be. Now, how annoying.
"And I watched and watched, and finally I realized that this little cloud was actually omega Centauri! Got my telescope on it and, sure enough, it was beautiful . . . Just thousands of stars and far more prominent, far more bright than M13."