Some of us like to put our Christmas tree up early, but the sky’s got a tree it never takes down. The Christmas Tree Cluster, a.k.a. NGC 6624, has been glittering in the evening sky for weeks. This beautiful clutch of suns in the shape of a Christmas Tree shines from the constellation Monoceros the Unicorn northeast of Orion’s bright, red star Betelgeuse. I’m not sure how well the ornaments are doing because it stands upside-down with tip pointing downward. But in a typical telescope, where south is flipped with north, stands up properly again.
It’s brightest star, S Monocerotis (mon-ah-ser-OH-tis), at the base of the tree is 4th magnitude and bright enough to see with the naked eye. It’s a white-hot, supergiant star 217,000 times more luminous and 35 times more massive than the sun. Like Betelgeuse to its southwest, S Mon is slated for supernova stardom sometime in the future.
The cluster’s about half a degree across, or about the same size as a full moon, and its triangular shape stands out even in binoculars. A telescope will show about 40 stars plus dabs of nebulosity here and there. The brightest patch lies just to the southwest of S Mon in the bottom “branches” of the tree.
The Christmas Tree is a young star cluster about 2,600 light years from Earth still swaddled in its birth clouds and includes three named objects: the star cluster proper, that bright nebular patch, nicknamed the Fox Fur Nebula, and the Cone Nebula. Most Christmas Trees are topped with an angel or star, but this one has a long, funnel-shaped cone made of dark, interstellar dust and gas. A 6-inch telescope will show the Fox Fur, but you’ll need a 10-inch or larger instrument for the Cone.
I hope you enjoy this starry tree in the night sky, and I wish you all a wonderful Christmas and happy holiday!