NGC 2264

NGC 2264 is a bright open cluster surrounded by a large system of diffuse nebulosities within the constellation Unicornus.

In fact, the first striking feature when exploring this area of the sky with binoculars is a group of about twenty blue stars, dominated by the star S Monocerotis, of magnitude between the fifth and the ninth, arranged in a triangle, with the vertex pointing southwards, a feature that in the southern hemisphere (where the top appears to be turned upwards) makes it similar to a Christmas tree (the latter is the proper name of the cluster).

At the southern vertex of the cluster, if observed with a Newtonian telescope with the aid of a filter, a nebula becomes evident, at the edge of which there is a dark cone-shaped patch with the tip pointing towards the vertex of the Christmas tree; this structure made the cloud famous under the proper name of the Cone Nebula. To the northwest of the cluster there is also a large, fainter nebulosity, which is clearly visible in the long-exposure photos