Noctilucent Cloud Sightings
The northern season for noctilucent clouds (NLCs) is underway, and the clouds are growing brighter. "Last night, we saw the first NLCs over Denmark," reports Ruslan Merzlyakov of Nykøbing Mors. He took this picture just one hour past midnight on June 2nd:
NLCs are Earth's highest clouds. Seeded by meteoroids, they float at the edge of space more than 80 km above the planet's surface. The clouds are very cold and filled with tiny ice crystals. When sunbeams hit those crystals, they glow electric-blue.
Noctilucent clouds first appeared in the 19th century after the eruption of super-volcano Krakatoa. At the time, people thought NLCs were caused by the eruption, but long after Krakatoa's ash settled, the clouds remained. In recent years, NLCs have intensified and spread with sightings as far south as Utah and Colorado. This could be a sign of increasing greenhouse gases in Earth's atmosphere.
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
Here’s one more picture.
We often say that noctilucent clouds are "electric blue." One glance at this photo from Kristianstad, Sweden, explains why:
"On Monday night, pale ripples spread across 90 degrees of the northern sky," says photographer Jonas Carlsson. "This is a great beginning to the 2015 season."
Since June began, sky watchers have seen noctilucent clouds over Ireland, Sweden, Denmark, Scotland and Russia. And more are in the offing....