Strange Clouds at the Edge of Space

Hi! I thought you'd be interested in this story from Science@NASA: High above Earth, astronauts on board the International Space Station have taken one of the best-ever photos of electric-blue noctilucent clouds. Their image, featured in today's story from Science@NASA, highlights a growing mystery: Where do these clouds come from and why are they spreading? http://science.nasa.gov/headlines/y2008/25aug_nlc.htm?friend