- NGC 2264 The Christmas Tree Cluster
NGC 2264 is a large, bright open cluster with associated nebulosity lying within the Winter Milky Way in the constellation Monoceros. It gets its common name from the observation that the brighter stars of the cluster appear to form the outline of a Christmas tree, with the stars representing lights on the tree. In my image above, the "tree" lies horizontally on its left side. The bright (visual magnitude 4.66) blue-white star 15 Monocerotis sits at the base of the tree. In this image, created from 5-minute exposures in the red, green and blue spectral bands, bright and dark nebulas can be seen within and around the cluster. Most conspicuous is the white-ish reflection nebula adjacent to 15 Monocerotis. William Herschel was the first to describe the cluster in 1784. A year later, he was the first to describe the nebula associated with it, saying that the stars of the cluster "are involved with extremely faint milky nebulosity which loses itself imperceptively." The designation NGC 2264 refers to both the cluster and the nebula.
The background of the cluster can be seen as glowing with the red light of Hα emissions. This emission nebula is quite extensive (see my Blog entry for 4 December 2016 for additional views of this nebula). This region comprises the main portion of the Monoceros OB1 Association, a birthplace for young stars. Around 250 young blue-white stars can be found populating this region, with another 360 hidden within the clouds of gas and dust. This region is thought to have condensed around 3 to 30 million years ago.
Physically, this large cluster (around 40 arc-min in diameter) lies at a distance of around 2600 LY and contains around 40 brighter member stars. It can be detected with the naked eye, and is a good object for viewing with binoculars or a small telescope.
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