ISS astronauts witnessed a display of noctilucent or “night-shining” clouds a month or so ago. Here’s a shot of then 320km above Mongolia.

Atmospheric scientist Gary Thomas of the University of Colorado has seen thousands of noctilucent cloud (NLC) photos, and he ranks this one among the best. “It’s lovely,” he says. “And it shows just how high these clouds really are–at the very edge of space.”

He estimates the electric-blue band was 83 km above Earth’s surface, higher than 99.999% of our planet’s atmosphere. The sky at that altitude is space-black. It is the realm of meteors, high-energy auroras and decaying satellites.

What are clouds doing up there? “That’s what we’re trying to find out,” says Thomas.

[…]

“It’s a puzzle,” says Thomas. “Noctilucent clouds have not only persisted, but also spread.” In the beginning, the clouds were confined to latitudes above 50 degrees; you had to go to places like Scandinavia, Siberia and Scotland to see them. In recent years, however, they have been sighted from mid-latitudes such as Washington, Oregon, Turkey and Iran

Science, you find so many beautiful things for me to ponder and write horror stories about.

(via science@nasa)