NGC 2264, commonly called the Christmas Tree Nebula, is a rich star-forming region in the constellation Monoceros. It actually comprises two main structures: the open star cluster known as the Christmas Tree Cluster and the surrounding emission nebula, which also contains the famous Cone Nebula. This region is illuminated primarily by the hot young star S Monoceros, whose radiation energizes the glowing clouds of gas and dust. The triangular arrangement of the cluster’s brightest stars gives the appearance of a Christmas tree in the night sky.