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