2016 January 30

Collinder 69 – an overlooked cluster in Orion

Stewart Moore

Orion contains a wealth of star clusters but one that often gets overlooked is Collinder 69 (the list of Cr clusters was compiled by the Swedish astronomer Per Collinder and published in 1931 as an appendix to his paper on structural properties of open galactic clusters). The cluster, which is estimated to be around 5 million years old and lying 1,300 light years distant, is associated with the magnitude 3.4 star Lambda Orionis (Meissa) and its two nearby 4th magnitude companions Phi-1 and Phi-2 which lie to the south. This little triangular grouping – occupying just over half a degree of sky – is normally taken as representing the head of The Hunter (see chart) and is a conspicuous binocular or small telescope asterism. There is also an interesting line of 3 mag 7 stars running north from phi-1 towards Meissa. There is however more to this cluster than these few stars and under a good sky medium sized binoculars will show many fainter stars within this half-degree area. In small binoculars the faint stars (as is often the case) give a nebulous feel to the cluster but what is interesting is that there really is nebulosity here and a 20 or 25 cm telescope plus OIII filter will show hints of the emission nebula around the brighter stars This nebulosity is catalogued as Sharpless 2-264. If you’ve never seen this lovely little cluster, the next few weeks are an ideal time to observe it (if we ever get a clear sky again that is). There are no images of this open cluster in the Deep Sky Section archives, so perhaps this can now be remedied.