Messier 83: The Southern Pinwheel Galaxy

Messier 83, the Southern Pinwheel, is one of the brightest spiral galaxies in the sky. It lies in the long constellation Hydra, far enough south that northern observers see it low over the horizon, while southern observers get a superb view.

What it is

M83 is a barred spiral galaxy seen nearly face-on, about 15 million light-years away. Its 11-arcminute disk is roughly 50,000 light-years across at that distance. Its arms are lined with dark dust lanes, clusters of young blue stars, and pink clouds of hydrogen where new stars are forming. Hubble images show hundreds of thousands of individual stars and thousands of star clusters, along with bubbles blown by nearly 300 supernovae over its recent history.

M83 has also been a rich source of supernovae seen from Earth; SEDS lists several during the 20th century. It belongs to a small group of galaxies that includes the radio galaxy Centaurus A.

When to see it

M83 is a spring object for northern observers. It crosses the meridian around midnight in mid-April and around 10 p.m. in mid-May. From 40°N it rises only to about 20° above the southern horizon, so you need a clear, flat southern view and a night with good transparency. From the Southern Hemisphere it is a highlight, passing nearly overhead around 30°S on autumn evenings.

How to find it

Start at Spica in Virgo and look about 12° due south for Gamma Hydrae, a 3rd-magnitude star. Then find Pi Hydrae, of similar brightness, about 11° east-southeast of Gamma. M83 forms a triangle with the two stars: it lies about 8° south-southeast of Gamma Hydrae and about 7° west-southwest of Pi Hydrae. Sweep that area slowly with binoculars or a finder.

What you will see

In binoculars M83 shows as a round, faint glow with a brighter center. A 70–100 mm telescope shows a fairly bright, roundish haze with a distinct, almost star-like core; from northern sites, its low altitude dims it. In a 200 mm telescope under a dark, steady sky the central bar becomes visible as an elongated brightening, and with care you can trace the beginnings of the spiral arms. From the Southern Hemisphere, where it stands high, the arms are much easier. Light pollution near the southern horizon is its worst enemy from the north.

History

Nicolas-Louis de Lacaille discovered M83 on February 23, 1752, from the Cape of Good Hope. It was the first galaxy found beyond our Local Group. Charles Messier added it to his catalog on February 17, 1781, noting that from Paris it was so faint he could see it only with great concentration. William Lassell later described its spiral structure as three-branched.