This is a close-up of the western part of the veil nebula I imaged previously in full scale. (North is left.)
The nebula is the remnant of an ancient cascade of supernovae that exploded a couple of tens of thousands years ago. I was able to capture the eastern part back in 2009.
You may notice the difference in star density between the inner part of the shell (lower) and the outskirts (upper). The reason is that the supernova blew away the interstellar matter and revealed plenty of faint background stars behind the shock front in contrast to those still obscured where the blast hadn't passed yet.