All That Glitters!

Polar Mesospheric Clouds, Northern Hemisphere by NASA Goddard Photo and Video on Flickr.

In both the Northern and Southern Hemisphere, during their respective late spring and early summer seasons, polar mesospheric clouds are at the peak of their visibility. Visible from aircraft in flight, the International Space Station (ISS), and from the ground at twilight, the clouds typically appear as delicate, shining threads against the darkness of space—hence their other names of “noctilucent” or “night-shining” clouds.