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.
Look west 30 to 60 minutes after sunset when the Sun has dipped 6o to 16o below the horizon. If you see luminous blue-white tendrils spreading across the sky, you’ve probably spotted a noctilucent cloud. Although noctilucent clouds appear most often at arctic latitudes, they have been sighted in recent years as far south as Colorado, Utah and Virginia. NLCs are seasonal, appearing most often in late spring and summer. In the northern hemisphere, the best time to look would be between mid-May and the end of August.