Let’s turn skyward once again, this time to the deep southern constellation of Carina. Here, along the edge of the southern Milky Way, star clusters stick out like dandelions in a spring field. Many clusters are visible here to the naked eye or binoculars. One the prettiest is NGC 2516, also called the “Southern Beehive” after its resemblance to the northern Beehive star cluster, M44, in the constellation Cancer.
Though this magnitude 3.5 cluster was clearly visible in prehistoric times, the Southern Beehive was first cataloged by the diligent Lacaille in 1751 with his tiny 1/2-inch telescope.
Transform your computer into a virtual observatory
A century later, John Herschel described the cluster as “a really superb object”, and noted an bright orange star dominated the cluster (there are actually two orange stars embedded in NGC 2516, so it’s not clear which one Herschel was referring to). Herschel counted more than 200 stars in the cluster; modern estimates put membership at 103 stars, including the two orange-red star of magnitude 5 and 6. Most of the stars are concentrated in a circle of 20-30′ (recall the full moon is 30′ across). The cluster is about 1300 light years from Earth, and the light you see now left these stars when the Mayan civilization was flourishing in Central America.
Like many star clusters, the fun of observing NGC 2516 lies in discerning patterns among the lines and streams stars apparently winding through the cluster. Astronomy writer Steve O’Meara sees among these stars the shape of a cat preparing to sleep on a soft cushion. I’ve seen more of a “brontosaurus” shape among these stars… though whatever you see, you’ll find this cluster quite lovely in binoculars or a wide-field telescope at 40-70x.
The Southern Beehive is also a favorite among professional astronomers. They’ve determined the cluster is a nest of chemically peculiar stars, meaning there are unusual amounts of metals in the atmospheres of many of the cluster’s constituents.
Also, NGC 2516 shares a common motion through space with seven other star clusters, including the Pleiades, IC 2602 (sometimes called the “Southern Pleiades”), and the alpha Persei cluster that surround Mirfak, the brightest star in Perseus. The common motion of these clusters suggest a common origin some 60-100 million years ago.
A guide to NGC 2516, as well as the “Southern Pleiades” star clusters
Since it’s visible to the naked eye, NGC 2516 is fairly easy to find, just 3.5 degrees southwest of epsilon Carinae (Avior). The Southern Pleiades star cluster lies nearby. Neither are visible north of 25-30 degrees north latitude. Next time, we’ll turn to a beautiful but challenging visual sight in the northern hemisphere.