Tonight – on April 16, 2017, and throughout April and May – let the sparkling blue-white star Spica act as your guide to the Omega Centauri star cluster. This year, in 2017, Spica will be easy to find because the dazzling planet Jupiter beams quite close to this star all year long. When Spica climbs highest up for the night, so does the Omega Centauri star cluster.
You can see this cluster with the unaided eye, if your sky is dark enough and if you’re far enough south on the Earth. People living south of 35o North latitude have a realistic chance of spotting the cluster over the southern horizon, though we’ve seen at least one report of Omega Centauri seen as far north as Point Pelee, Canada (42o north latitude). Omega Centauri looks like a fairly faint (and possibly fuzzy) star. And of course it’s awesome from the Southern Hemisphere. It’s a beautiful and very special star cluster, and – if you’re in the Northern Hemisphere – it’s convenient to let Spica help you find it. Follow the links below to learn more.
What is Omega Centauri? Omega Centauri is the largest and finest globular star cluster visible to the eye alone. Globular clusters are large, symmetrically shaped groupings of stars, fairly evenly distributed around the core of our Milky Way galaxy. Many northern stargazers have this particular cluster on their bucket lists.
Seeing Omega Centauri is very special in part because you can see it with your eye alone, assuming you have a dark-enough sky. Very few of the Milky Way galaxy’s 250 or so globular star clusters are readily visible without optics.
Like all globular clusters, Omega Centauri is best seen through a telescope. Then you see it as a globe-shaped stellar city, teeming with its millions of stars!
Here’s how you can find Spica. Spot this star by extending the curve of the Big Dipper handle, as illustrated on our chart above.
Spica transits – climbs to its highest point in the sky – around 11:45 p.m. local standard time (12:45 a.m. daylight saving time) around mid-April for all locations around the globe. With each passing week, Spica will transit a half hour earlier. In late April/early May, Spica’s transit time will be approximately 10:45 p.m. (11:45 p.m. daylight saving time). You can find Spica’s (or Jupiter’s) precise transit time for your sky at the US Naval Observatory.
Here’s the key to using Spica to find Omega Centauri. Spica and Omega Centauri transit due south at virtually the same time. That means that – when Spica is highest in the south – Omega Centauri is, too. Look for Omega Centauri about 35o directly below Spica. A fist at an arm-length approximates 10o.
What if I’m in the Southern Hemisphere? As seen from the Southern Hemisphere, Spica and Omega Centauri pass more nearly overhead. They still transit at approximately the same time. They still are located about 35 o apart. Unfortunately – because the Big Dipper is located so far north on the sky’s dome – it’s less convenient to use the the Dipper to find Spica and, from it, Omega Centauri.
From the Southern Hemisphere, you’ve got an even more beautiful way to find this cluster. And, indeed, your view of the cluster will be better than ours in the north, because Omega Centauri will be higher in your sky.
To get in its general vicinity on the sky’s dome, look for the famous Southern Cross, which, officially, is the constellation Crux. Along the eastern edge of Crux is the dark Coalsack Nebula. Near the Coalsack – visible in binoculars – is the Jewel Box, an open star cluster with about 100 members, whose stars are colored red, white and blue.
If you can locate these objects, you’ll also find Omega Centauri. Consult the charts at right for its location.
Bottom line: From the Northern Hemisphere, you can use the star Spica in the constellation Virgo to locate Omega Centauri on springtime nights!