Globular cluster M 15 augmented with narrow band filters to enhance planetary nebula Pease 1 (red object lower right of core). Pease 1 was the first planetary nebula found in a globular cluster. It was initially noted to appear very bright on a photographic plate using a Pulkovo ultra-violet filter compared to neighboring stars (otherwise of about equal magnitude). Subsequent spectrographic study revealed green lines of oxygen characteristic of planetary nebulae as well as red lines of hydrogen. A larger version is available here: http://whwastro.homestead.com/files/M15-f10-2008-800r.jpg Here's a nice article on the topic by Leos Ondra: http://www.seds.org/MESSIER/xtra/leos/pease1.html