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NGC 7635, also called the Bubble Nebula, is a H II region emission nebula in Cassiopeia. The "bubble" is created by the stellar wind from a massive hot, young central star

The image was made using Atic One-6.0 CCD camera which has integral Off-Axis guiding, on an Altair 250mm RC telescope and Skywatcher AZ EQ6-GT mount. Luminance (H-alpha) exposure was 80 minutes (in 200sec subs) and R,G,B exposures 16.67 minutes (in 200sec subs). Processed in Maxim DL to create the LRGB composite then in Photoshop for the final image.
The image on the left uses a Hydrogen-alpha filtered image as the luminance channel while the one on the right uses a normal unfiltered image. I prefer the H-a version because it enhances the nebula itself and produces much smaller stars. After all, most of the stars are nothing to do with the nebula. It also retains some colour in the stars.
[Alan Jefferis]