Astronauts onboard the International Space Station have been observing electric blue "noctilucent" clouds from Earth-orbit.

They hover on the edge of space. Thin, wispy clouds, glowing electric blue. Some scientists think they're seeded by space dust. Others suspect they're a telltale sign of global warming.

They're called noctilucent or "night-shining" clouds (NLCs for short). And whatever causes them, they're lovely.

"In January 2003 we enjoyed outstanding views of these clouds above the southern hemisphere," said space station astronaut Don Pettit during a NASA TV broadcast in January 2003."We routinely see them when we're flying over Australia and the tip of South America."

Sky watchers on Earth have seen them, too, glowing in the night sky after sunset, although the view from Earth-orbit is better. Pettit estimated the height of the noctilucent clouds he saw at 80 to 100 km ... "literally on the fringes of space."