The official designation for this planetary nebula is PK205+14.1. It is also listed as Abell 21 and Sharpless 2-188. It is a very large PN in Gemini perhaps 10 arcmin in diameter. The brighter portion pointing to the SE gives it a crescent moon appearance, but closer inspection shows fainter regions toward the NW. Thus, it probaby has an ellipsoidal shape. North is to the lower left.
This image, taken on the WayBack Machine (16" RC) is comprised of 6 nm H-a mapped to red and 3 nm OIII mapped to equal mixtures of green and blue to enhance contrast and bring out the incredible structure within the PN. Star colors were blended in from G2V-balanced RGB data.
DG Imaging 
