20 Minutes of Planetary Nebulae (except 4 minutes for me because the new blogger sucks)

http://en.wikipedia.org/wiki/Planetary_nebulae

http://www.noao.edu/jacoby/

http://www.seds.org/messier/planetar.html

http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula/Planetary.html

http://www.astro.washington.edu/balick/WFPC2/

APOD 3.5

Hydrogen ions make the red glow, but the true source of the nebula located in Orion is unknown due to interstellar dust, which we recently learned about.