- M 39 (NGC 7092)
M 39 is a large, sparse open cluster lying within the Summer Milky Way stream in the constellation Cygnus. It was first described by Charles Messier in 1764. This cluster has only around 30 definite member stars, with the others in the image being background Milky Way stars. M 39 has a physical diameter of only around 9 LY. The fact that it is relatively close to us (1000 LY) accounts for its large visual size (around 0.5 degree across). The stars in the cluster are all of spectral classes A and B, which indicates a relatively young age (240-280 million years) for the cluster. M 39 has a visual magnitude of 4.6, but is pretty much lost in the surrounding brightness of the Milky Way stream.
The bright yellow-orange star in the upper right corner of my image is the Cepheid variable V1726 Cygni, which is part of a small, loose open cluster Platais 1. Another interesting feature in my image is the linear string of small stars in the upper left corner. This asterism is reminiscent of Kemble's Cascade in the constellation Camelopardalis, on a much smaller scale.
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