Tuesday night was no different.
Astute observers from around the northern latitudes of the world noticed a dazzling display of "noctilucent" clouds.
They are clouds at the very edge of space, hundreds of thousands of feet in the air. The air is very cold and very dry at that level of the atmosphere, but in the summer time, the rising air from the hotter surface can gradually push a little water moisture to those space-high altitudes (that's why they're seen only in the summer). Scientists are still not quite sure of all the details that cause the clouds to form, although the glow is from simple sunlight -- the clouds are so high they reflect sunlight even after the sun appears well below the horizon from the ground.
There are theories that volcanoes can cause them -- and as you saw, we just had a big eruption of a volcano in Russia last month -- while another suggested it could also be tied to Space Shuttle exhaust, although there hasn’t been a recent shuttle launch this time.
Anyway, sightings used to be limited to areas above 50 degrees north latitude, but spaceweather.com says the clouds are being seen at lower and lower latitudes these days -- obviously we've seen it a few times here in the Northwest between 45-48 degrees north, and there was a sighting in Nebraska Tuesday night, which is down at 41 degrees north.
(See a gorgeous gallery of the clouds around the world here, including a great shot of the clouds behind fireworks in France celebrating Bastille Day.)
The clouds are expected to be out again Wednesday night, and local weather should cooperate, so if you're out and about tonight, see if you can spot them and if so, e-mail them to me and I'll feature them in Thursday's blog.
Here are more local photos, all taken by Robert and Jennifer More in Seattle who saw them just before 4 a.m. Wednesday morning: