Hi

I was looking at this DSS image of the ACO2151 Hercules cluster of galaxies. Is the somewhat elongated faint, ring-like structure just north of the core a giant planetary nebula, or just an optical defect? It must be the latter, right?

http://pw2.netcom.com/~ahighe/A2151_60_60F.jpg

Clear Skies

Regards
Akarsh