NGC 7635, aka the “Bubble Nebula”, is an emission nebula in Cassiopeia measuring about 8 x 15 arcminutes — it’s approximately 10,000 light years distant. The central portion of the nebula, containing the Bubble itself, was formed through the actions of a stellar wind from a massive central star. This is mostly a narrowband rendition — contrast this image with my earlier attempt (2007).
Technical details are as follows:
RGB imaging at MYHY Observatory in the Philadelphia suburbs in 2007 using a 12.5″ OGS RC; Ha and OIII data using the RC and a Tak FCT-150, respectively, were added in 2018 — all photons captured with the SBIG STL11K on a Paramount ME with 12 hours of Ha, 20 hours of OIII, and 4.5 hours of RGB data. Calibration in Maxim, alignment and integration in PixInsight, and the rest in Photoshop. It was assembled as an Ha/OIII bicolor image (Steve Cannistra’s technique) with RGB stars.