I was quite surprised when not just two but three gas shells were captured after 6 hours of hydrogen alpha exposures in this image of planetary nebula NGC2438! I decided to do a long Ha exposure after I noticed hints of a second outer shell in a red POSS2 image. The magnitude 10 planetary nebula is in the foreground of M46, a beautiful open star cluster in the constellation Puppis.
n earlier image by Don Goldman that captured the second gas shell can be found here: http://dg-imaging.astrodon.com/gallery/display.cfm?imgID=206
