This is NGC 281, The Pacman Nebula in Cassiopeia. Also catalogued as IC 11, Sh2-184, Sharpless 184, LBN 616 and LBN 123.
NGC 281 is a bright emission nebula, and part of an H II region, in the northern constellation of Cassiopeia; it is part of the Milky Way's Perseus Spiral Arm. This 20×30 arcmin sized nebulosity is also associated with open cluster IC 1590, several Bok globules, the multiple star B1, and measures over 50 lightyears across. A recent estimate of its distance shows it lies around 9200 lightyears from us. It is known as the Pacman Nebula for its resemblance to the video game character.
E. E. Barnard discovered this nebula in August 1883, and described it as "a large faint nebula, very diffuse." The nebula region is visible in amateur telescopes from dark sky locations.
This image is comprised of 120x180sec lights, 40 each through Ha, Sii and Oiii filters, with all of the associated Flats, Darks and Bias, and represents around 6hrs exposure (not including the calibration frames). It was taken over the course of 3 nights last week.
The image was processed in PixInsight, with Sii mapped to Red, Ha mapped to Green and Oiii mapped to Blue. The colour channels were then adjusted independently to produce the classic Hubble Palette, where the red and ochre colours represent predominantly Ha emissions (with a little Sii), with the blues and cyans representing the Oii emissions.