Gather ‘Round The Cosmic Christmas Tree

The Christmas Tree Cluster in Monoceros adds sparkle to the sky this holiday season. If you’re having difficulty seeing the tree, see the version below. South is up. ESO

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.

There it is! Attached to the tree like ornaments are the Fox Fur and Cone nebulas. South is up. ESO

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.

To find the Christmas Tree Cluster start at Betelgeuse in Orion. The 2nd magnitude star Alhena in Gemina lies about 10° (one fist) to the left or east of Betelgeuse. Focus your glass on Alhena and the cluster’s just a short hop below. Remember — the Tree will be upside-down in binoculars. Stellarium

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’ve circled the Christmas Tree in this simulation of its appearance in a pair of 10×50 binoculars with normal directions (north up). The brightest star in the cluster is S Monocerotis. Field of view is about 5°. Stellarium

I hope you enjoy this starry tree in the night sky, and I wish you all a wonderful Christmas and happy holiday!

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