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.
Technical details are as follows:
Data was acquired in 2007 at MYHY Observatory (in the Philadelphia suburbs) using a 12.5″ OGS RC — all photons were captured using the SBIG STL11K on a Paramount ME. The image includes 6 hours of RGB data. Calibration in Maxim, alignment in Registar, and integration in Sigma Combine; the rest in Photoshop. The image was assembled as an (R)(RGB). For comparison, check out the Ha/OIII narrowband version HERE.