Sh2-284 (also known as the Smiling Cat Nebula and LBN 983), is located approximately 4033 parsecs (13157 light-years)  away from Earth in the constellation Monoceros, just 5 degrees southeast of the more popular and similarly-sized Rosette nebula.  In the center of the head of the cat  (itself, about about 150 light-years across) is a collection of young and energetic mostly hot blue-white (10 O and B type and 1 F supergiant) stars that form the open cluster known as  Dolidze 25. These stars provide the ionizing UV energy  that blow out from the cluster, stripping electrons off of first of the Ha then Sii, carving out the core of bright green then rim of orange revealing the Ha and  Sii signal, respectively, in this SHO composition. Denser areas of interstellar material leave behind a variety of pillars and dark nebula. An interesting publication in 2015 by Negueruela et al. confirmed and expanded on earlier work on Dolidze 25 with spectral data revealing stars of very low metallicity. In fact, this open cluster contains stars of the lowest metallicity of any stellar nursery in the Milky Way because of the eccentric location of this target well away from the galactic center; Sh2-284 is located near the galactic anticenter, in the far periphery of the Norma (Outer) arm of the Milky Way. Stars this far out on a spiral arm far from the galactic center have undergone less recycling than higher metallicity stars near the denser galactic center. From  Evan Gough on the Universe Today website: "Our galaxy has a metallicity gradient. Stars nearer the galactic center have higher metallicity than stars near the periphery. The higher metallicity is because they formed from material enriched by previous generations of stars. Since there are more stars being born and dying nearer the galactic center, stars recently born in that region form from material that’s been enriched by the stellar birth/death cycle. But Sh2-284 and Dolidze 25 are located near the galactic anticenter. They’re relatively isolated out on the end of one of the Milky Way’s spiral arms."

Other notable components of the nebula include:  The round IR "bubble" that forms the eye of the cat which is designated E80  [HKS2019]; another "bubble" E84 outside the head in the upper left of this image; LBN 986, forming the bright "ear" of the cat; LBN 987 forming the neck, including the dark pillars forming the smiling mouth.  There is a strong OIII signal to the north (right in this image) of the Cat Head, and the bright small round nebula to the  center-right is BFS 53 (Brand, Fich and Stark),  which is actually a foreground object at a distance of 1900 parsecs (nearly 6,200 light years).

While I am typically not a fan of green in astro images, this SHO version was the most compelling of all of the combinations, including HSO and HOS versions.  The Mouseover in Version B is a normalized version of this SHO image using  [url=https://www.astrobin.com/users/WB91/]@Bill Blanshan 's and @Mike Cranfield's  excellent tools.