Celestial Treasures of the Constellation Centaurus

the constellation centaurus
The constellation Centaurus with Crux and Omega Centauri. Carolyn Collins Petersen

It's not often that people from the northern hemisphere get to see southern hemisphere stars unless they actually travel south of the equator. When they do, they come away marveling at how lovely the southern skies can be. In particular, the constellation Centaurus gives people a look at some bright, nearby stars and one of the loveliest globular clusters around. It's definitely worth looking at on a nice, clear dark night.

Understanding the Centaur

The constellation Centaurus has been charted for centuries and sprawls across more than a thousand square degrees of sky. The best time to see it is during the evening hours during southern hemisphere autumn into winter (around March through mid-July) although it can be spotted very early in the morning or evening other parts of the year. Centaurus is named for a mythological being called a Centaur, which is a half-man, half-horse creature in Greek legends. Interestingly enough, due to Earth's wobble on its axis (called "precession"), Centaurus's position in the sky has changed over historical time. In the distant past, it was seen from all over the planet. In a few thousand years, it will once again be visible to people around the world.

Exploring the Centaur

Centaurus is home to two of the most famous stars in the sky: the bright bluish-white Alpha Centauri (also known as Rigel Kent) and its neighbor Beta Centauri, also known as Hadar which are among the Sun's neighbors, along with their companion Proxima Centauri (which is currently the closest one).

The constellation is home to many variable stars as well as a few fascinating deep-sky objects. The most beautiful is the globular cluster Omega Centauri. It is just far enough north that it can be glimpsed in late winter from Florida and Hawai'i. This cluster contains about 10 million stars packed into an area of space only about 150 light-years across.

Some astronomers suspect there may be a black hole at the heart of the cluster. That idea is based on observations made by the Hubble Space Telescope, showing stars all crowded together at the central core, moving faster than they should be. If it does exist there, the black hole would contain about 12,000 solar masses of material.

There's also an idea floating around in astronomy circles that Omega Centaurus might be the remains of a dwarf galaxy. These small galaxies still exist and some are being cannibalized by the Milky Way. If this is what happened to Omega Centauri, then it occurred billions of years ago, when both objects were very young. Omega Centauri may be all that's left of the original dwarf, which was torn apart by the close pass by the infant Milky Way.

Spotting an Active Galaxy in Centaurus

Not far from the vision of Omega Centauri is another celestial wonder. It's the active galaxy Centaurus A (also known as NGC 5128) and is easily spottable with a good pair of binoculars or a backyard-type telescope. Cen A, as it's known, is an interesting object. It lies more than 10 million light-years away from us and is known as a starburst galaxy. It's also a very active one, with a supermassive black hole at its heart, and two jets of material streaming away from the core.

Chances are very good that this galaxy collided with another one, resulting in huge bursts of star formation. The Hubble Space Telescope has observed this galaxy, as have several radio telescope arrays. The core of the galaxy is quite radio-loud, which makes it an attractive area of study.

Observing Centaurus

The best times to go out and see Omega Centauri from anywhere south of Florida begin in the evening hours of March and April. it can be seen into the wee hours until July and August. It's south of a constellation called Lupus and seems to curl around the famous "Southern Cross" constellation (officially known as Crux). The plane of the Milky Way runs nearby, so if you go to view Centaurus, you'll have a rich and starry field of objects to explore. There are open star clusters to search out and a lot of galaxies!

You'll need binoculars or a telescope to really study most of the objects in Centaurus, so get ready for some busy exploration!