Mysterious Clouds of Summer Nights
The Noctilucent or night-shining clouds (NLCs) appear in a clear summer evening of Sweden. While nights of June and July at this latitude (about 60 degrees) never get dark enough to see many stars, the NLCs are bright enough to be seen in this mid-night twilight. NLCs lie near the edge of space, reflecting sunlight from about 80 kilometers above Earth’s surface. They are usually spotted above the Polar Regions in summer.