September 30, 2008

In Today's One Minute Astronomer...

NGC 6193: The "Four-In-One" Cluster

This young star cluster in the southern skies was born just 3 million years ago from gas and dust compressed by a nearby supernova explosion. Graced by hot blue stars and generous remnants of glowing gas in nearby NGC 6188, this region in the constellation Ara reveals an open star cluster, a reflection nebula, an emission nebula, and dark nebula all in one place.

The Basics

• NGC 6193 only has 15-20 stars. But it's a beautiful object for connoisseurs of open clusters. This cluster and the surrounding patch of sky contain new stars, glowing red gas from which the stars formed, dust clouds that reflect the blue light of the new stars, and dark clots of dust that linger about the region.

• The cluster and its nearby nebula are part of a wider group of young bright stars called the Ara OB1 Assocation, located roughly 4,000 light years from Earth. This association is a small part of a dynamic spiral arm of the Milky Way that's splintering into new stars at this very moment.

• If you're lucky enough to live under dark southern skies, you'll easily find this cluster 7 degrees southwest of the star zeta Scorpii and 2 degrees southeast of epsilon Normae. As a compact cluster, it's easy to see in binoculars or a small telescope.

NGC 6193 in Ara. Coordinates: RA16h41.3m Dec -48d46m

A Deeper Look

• The brightest star in NGC 6193 is the blazing hot HD150136. It's a fine multiple star. Its furthest companion is 9.6 arc-seconds to the west and is easily seen in a small telescope. Another companion is much harder to see, and yet another is impossible to see in a telescope: it's so close it's nearly touching the main star.

• HD150136 and many other stars in the cluster are massive and burn very quickly. Millions of years hence-a short time compared to the life of a small star like our sun-- they will produce spectacular supernova explosions.

• While the cluster NGC 6193 is easy to see in binoculars, you'll need a larger telescope to detect the associated nebulae.

Star cluster NGC 6193 and emission/reflection nebula NGC 6188 in Ara. Associated dark nebulae block out background light. You won't see color or detail like this through your telescope.

Good To Know

A comparable, though much more sprawling region visible from northern skies can be seen near and just north of the star Alnitak, the easternmost star in Orion's belt.

Personal View

Like many southern splendors, I've only seen this one with the naked eye. In dark sky, it simply looks like a star set in a rich region of the Milky Way just south of Scorpius. So if you're under southern skies with a 10-12 inch telescope, take a look at this wonderful cluster and tell me what you think.

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