Sky watchers in Europe are reporting an outburst of bright noctilucent clouds (NLCs). The display began at sunset on July 3rd, filling northern horizons with electric-blue ripples, swirls, and tendrils of light. Morten Ross sends this picture from Sandbukta, Norway:
Noctilucent Cloud
© Morten RossTaken by Morten Ross on July 4, 2014 @ Sandbukta, south of Oslo, Norway.

"An incredibly bright and widespread display - from northern horizon to zenith!" says Ross. "This is only the third night of July and its already much better than last year." Similar reports have come from France, Germany, Poland, the Netherlands, Scotland, Ireland, England, Estonia and Belgium.

Although most of the reports so far have come from Europe, the nights ahead could bring NLCs to North America as well. Monitor the realtime gallery for updates.

NLCs are Earth's highest clouds. Seeded by "meteor smoke," they form at the edge of space 83 km above Earth's surface. When sunlight hits the tiny ice crystals that make up these clouds, they glow electric blue.

NLCs appear during summer because that is when water molecules are wafted up from the lower atmosphere to mix with the meteor smoke. That is also, ironically, when the upper atmosphere is coldest, allowing the ice crystals of NLCs to form.

The natural habitat of noctilucent clouds is the Arctic Circle. In recent years, however, they have spread to lower latitudes with sightings as far south as Utah and Colorado. This will likely happen in 2014 as well. Observing tips: 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 may have spotted a noctilucent cloud.