Links

http://en.wikipedia.org/wiki/Planetary_nebula
http://en.wikipedia.org/wiki/Cat
http://en.wikipedia.org/wiki/Dumbbell_Nebula
http://chandra.harvard.edu/photo/2001/1220/index.html
http://en.wikipedia.org/wiki/List_of_planetary_nebulae
http://en.wikipedia.org/wiki/Little_Ghost_Nebula
http://en.wikipedia.org/wiki/Hourglass_Nebula
http://www.noao.edu/jacoby/
http://zebu.uoregon.edu/~imamura/208/feb22/feb22.html
http://ad.usno.navy.mil/pne/gallery.html
http://www.astro.rug.nl/~pns/
http://www.astro.washington.edu/balick/
http://www.daviddarling.info/encyclopedia/P/planneb.html
http://stsdas.stsci.edu/elcat/