M35 (NGC 2168) on the left is a relatively loose open cluster about 3000 ly away and to our view, about the size of the full-moon. It is also known as the Shoe-Buckle cluster, but that needs some imagination, as it looks pretty random to me. Within the central 12 ly there are between 1600 and 3200 solar masses. At least 300 stars are certainly part of the cluster. Since the cluster is young at “only” 175 Myr there are many young blue stars. Much of the original gas that produced the cluster has dissipated, but there is still some gas that can be seen around the blue stars.

NGC2158 looks like a globular cluster and was initially thought to be just that. It is now known to be an open cluster. NGC2158 is much further away, at over 15,000 ly, much more compact, and much older, about 2 billion years, and thus consists of old low metallicity stars. So, unlike M35, NGC2158 is dominated by older yellower and redder stars. However, it contains 40 blue straggler stars These are old blue stars, not young blue stars, but they have stayed on the main sequence for longer than normal by gaining additional mass over time. 

Processing. This was a “full-moon-what-can-I-image project”. With the full moon and my severe LP I decided to use my L-eNhance and L-eXtreme NB filters, both worked well and helped the brighter stars from bloating too much. I decided I needed to do a mosaic to get this field without feeling it was squeezed in, to allow some space for the clusters to breathe. And in the end, I needed three nights total to get fainter stars in NGC2158. This is my first mosaic, a simple 2-panel, but it has given me amazing respect for those of you out there who do complex mosaics. DeepSkyStacker does have a mosaic mode, but it would not align properly for me in this case. And manually aligning in Photoshop was a bear. Both panels were stacked separately with DSS, then each processed in Startools. The mostly final images were then merged in Photoshop, and NoiseXterminator did a great job improving the stars while reducing noise.