Messier 23 (AKA NGC 6494) is an open cluster in Sagittarius. Being in Sagittarius, the background is full of gas and dust and stars giving it a spectacular backdrop.

The cluster is about 2,000 light years away so the light we are seeing today started on its journey when Rome was throwing its weight around in the Mediterranean. The cluster is estimated to contain a few hundred stars and to be about 330 million years old.

This was a relatively short integration of 7h 45m of HaLRGB data. For the technical details, see astrobin.