DSO of the Month :
NGC 2264
AKA: Christmas Tree Cluster
Position: 06 hrs 40 min 52 sec + 09 degrees 52 min 37 sec
Due south at 23:01 (GMT) on 15 January 2022
NGC 2264
Image: Les Brand, HAS member. Used with permission.
I have included this DSO for its obvious seasonal connotations, but put it in January rather than December because it is closer to the meridian in January evenings. There is a lot going on here. The Christmas Tree Cluster is an open star cluster and that will be our main focus of attention. However this cluster is surrounded by nebulosity which is an emission nebula, sometimes called the Fox Fur Nebula. There is a dark nebula at the base of the cluster, which is the Cone Nebula. However the Fox Fur Nebula and the Cone Nebula cannot easily be seen in a small telescope in a light-polluted area. The “Christmas tree” is upside-down, but would appear the right way up in a reflector; it is an outline shape of a tree like a cookie cutter. The whole area is a stellar nursery and the young stars in the cluster are partly hidden by dust clouds, and it is thus similar to both the Orion Nebula (M42) and the Eagle Nebula (M16).
The cluster is 2,400 light years away and lies in the modern constellation of Monoceros. The stars in the cluster are between one and ten million years old. They are a varied group, including T Tauri type stars (see Star of the Month for December 2020) and hot massive A type stars. At the base of the cluster where the pot for the tree would be is S Monocerotis (also called 15 Monocerotis) which is a massive O type star of magnitude 4.7 which is an irregular variable. It is part of the cluster and not a field star. The cluster was first noticed by William Herschel in 1784 and he saw the surrounding nebulosity the following year. The name “Christmas Tree Cluster” was apparently coined by Robert Burnham, first being mentioned in his Celestial Handbook of 1978. The name “Cone Nebula” is older, dating back to at least 1959. Being magnitude 4, it is a naked eye cluster in dark sky areas, but in Havering you will need binoculars or a small telescope to see it. To find it draw a line between Bellatrix and Betelgeuse in Orion and then continue this line to the west almost twice as much again. It is roughly half-way between Betelgeuse and Procyon, and directly beneath Gamma Geminorum (Alhena). It is just above NGC 2244, the Rosette Nebula.
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