May 6, 2008

In Today's One Minute Astronomer...

M83, "The Southern Pinwheel" Galaxy

Today, we have something for those of you in southerly locations: the spiral galaxy M83, lovely as a lotus blossom and one of the showpieces in the southern deep sky.

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The Basics

• Barely visible from northern latitudes, M83 lies roughly 15 million light-years away in the constellation Hydra. It's one of the 25 brightest galaxies in the sky, and one of the closest and brightest barred spiral galaxies. At magnitude 7.6, it's easily visible with binoculars and small telescopes.

• You'll find the "Southern Pinwheel" about 18 degrees due south of the bright star Spica, in Virgo.

• This galaxy was first seen by French astronomer and cartographer Nicolas Louis de Lacaille in 1752 during an expedition to the Cape of Good Hope. Lacaille charted nearly 10,000 southern stars and explored and mapped the region around the Cape before returning to France.

A Deeper Look

• M83 forms a small physical group, called the M83 group, along with the peculiar radio galaxy Centaurus A (also called NGC 5128)

• The shape of M83 lies between that of a normal and barred spiral galaxy. In photographs, it displays well-defined spiral arms flecked with red and blue knots. The red are diffuse gaseous nebulae where new stars form and which glow from the energy of hot young stars. The blue are congregations of new stars that have blown away the gas and dust of the nebulae from which they formed.

M83 from Kitt Peak National Observatory

Good To Know

Six supernovae have been discovered in M83 in the last 85 years. This is unusual because an average galaxy produces roughly one supernova every 300 years. The brightest supernova in M83 was discovered by the amateur astronomer J.C. Bennett from Pretoria, South Africa. His was the first discovery of a supernova by an amateur astronomer in the 20th century.

Personal View

I've never seen M83. From where I live, it's above the horizon but usually lost in the dewy murk of late (northern) spring. But northern observers can see a similar galaxy, M101- the Pinwheel Galaxy- in Ursa Major.