Tonight, let the sparkling blue-white star Spica act as your guide to the Omega Centauri globular star cluster. You can see this cluster with the unaided eye, if your sky is dark enough. Omega Centauri looks like a fairly faint (and possibly fuzzy) star. It’s a beautiful and very special star cluster, and Spica can help you find it.
You can spot the Spica 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 – at 10 to 11 p.m. local standard time (11 p.m. till 12 midnight daylight saving time) in early May for all locations around the globe. You can find Spica’s precise transit time for your sky at the US Naval Observatory.
As seen from the Northern Hemisphere, Spica and Omega Centauri transit due south at 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.
Omega Centauri is 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. Globular clusters are large, symmetrically shaped groupings of stars, fairly evenly distributed around the core of our Milky Way galaxy. Omega Centauri is the largest globular and finest globular star cluster visible to the eye alone.
People living south of 35o north latitude have a realistic chance of spotting Omega Centauri, though it’s been seen as far north as Point Pelee, Canada (42o north latitude). Best appreciated with a telescope, Omega Centauri, the largest and brightest of all globular star clusters, is a globe-shaped stellar city, teeming with millions of stars!
Bottom line: Use the star Spica in the constellation Virgo to locate Omega Centauri on these springtime nights!