A stargazer scanning the Milky Way through Crux and Centaurus is like a kid in a candy store, giddy with excitement at the sparkling treasures close at hand. This is a favoured part of the heavens for deep sky observers. When you take time to scan this area, be sure to pause at the lovely Pearl Cluster (NGC 3766), one of the richest clusters in a patch of sky already spoiled for riches.
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Like much in this part of the sky, the Pearl Cluster was born in the vast Carina star factory, an expanse of dust and gas associated with many massive stars including the barely-stable eta Carinae, which will one day detonate as a spectacular supernova. The cluster is about 5,800 light years away, and was formed in a long-dispersed emission nebula about 24 million years ago. You’ll sometimes see images of the Pearl Cluster with a large red nebula nearby. This is the Bat Nebula, IC 2948. It’s too faint to see visually in binoculars or a small scope.
Look for the Pearl Cluster about halfway between Acrux, the star at the foot of the Southern Cross, and the famous Eta Carinae Nebula. It’s just north of lambda Carinae, which itself has some nebulosity. The Pearl Cluster makes an excellent binocular target, and is sometimes visible in excellent sky without optics. It’s a dense open cluster, somewhat like the splendid Wild Duck Cluster in Scutum (LINK), or perhaps M37 in Auriga.
As always, look for colour in the cluster’s stars. In such a young group, most stars are blue. But some have morphed into red giants as they begin burning heavier elements in their cores.
NGC 3766 was discovered by our old friend Lacaille in 1752 with his little 1/2-inch telescope.