The Small Magellanic Cloud

Posted by Brian Ventrudo

Now to one of the finest sights in the deep-southern heavens, the Small Magellanic Cloud in the constellation Tucana, the Toucan. Named after navigator Ferdinand Magellan, the clouds are small neighboring galaxies of our own Milky Way and two of the very few galaxies visible to the unaided eye.

The Magellanic Clouds were once called the “Cape Clouds” by Dutch and Portuguese navigators after the Cape of Good Hope in South Africa, a major point of navigation. And in Johann Bayer’s famous 1603 star atlas Uranometria, the cloud was called Nubecula Minor (the “little cloud”). The clouds are only visible from the south of 20º N latitude.

Without optics, the SMC appears as a hazy patch some 4°x3° across. To some, in binoculars, it takes on the shape of a comma or a “fish hook”. The SMC is an irregular galaxy, too small to form the elegant spiral shape of larger galaxies like the Milky Way. The SMC is just 7,000 light years wide compared to a diameter of 100,000 light years of our own galaxy.

The Large and Small Magellanic Clouds (click to enlarge).

The wider, brighter part of the SMC extends slightly to the south. In a wide-field telescope, few of the SMC’s stars can be resolved. It is simply too far away, roughly 200,000 light years. But there is some subtle structure to be observed. Look especially at the northern edge of the SMC for four or five faint nebulae and unresolved star clusters. The brightest is NGC 346, a star-forming region and open star cluster just northeast of the centroid of the SMC. This region is about 200 light years across and contains a gaggle of young stars just 3 million years old. It bears resemblance to the Orion Nebula in our own galaxy. As you inspect NGC 346, try a UHC or OIII filter to bring out the contrast of it and smaller nebulae. Start at low-power and work your way to higher power to improve the contrast.

The Small Magellanic Cloud, right, and 47 Tucanae. Image credit Stephane Guisard/APOD (http://apod.nasa.gov/apod/ap071001.html)

As you examine the SMC, you will see a fuzzy “star” just a few degrees to the west. This is the splendid globular cluster 47 Tucanae, the second-brightest glob in the entire sky and a dazzling sight in a small telescope.