Number 173 in the Sharpless-2 catalog of hydrogen emission targets in the Northern Hemisphere, aka the Phantom of The Opera Mask Nebula. This is in the constellation Cassiopeia, some 8800 light years away. The descriptions of this tend to include phrases light "very difficult" and "extremely faint". Huh. I pointed the 5” refractor at it for one short and one long night (the latter was 9 PM to 4:30 AM) and here we are. Just can’t beat that telescope!

Processing on this one was a more interesting story than usual since it only has one narrowband channel, and I wanted to synthesize a more-accurate portrayal of hydrogen emission than just bashing the Ha data into the red channel. So instead I started with a color that more nearly represents the sum of H-alpha, H-beta, and H-gamma emission, and used the H-alpha data to modulate its brightness.

Nine and a half hours of Ha exposure plus a couple hours of RGB for the stars. Had to go down to 30" exposures for the stars to retain good saturation.