This week, reports started ramping up about eerie electric-blue clouds shimmering in nighttime skies in high-latitude regions. The stunning outburst of noctilucent, or night-shining, clouds hails the start of viewing season for these glowing, hypnotically dancing swirls.
The eye-catching wisps show up every year around local summer, and in the Northern Hemisphere sky-watchers can catch a glimpse of them painting the skies from now through August. Viewers in the Southern Hemisphere, meanwhile, should look for the clouds from November to February.
These mysterious, thin veils of clouds appear to form around Earth’s polar regions in the mesosphere, the highest level of Earth’s atmosphere. At these heights near the edge of space, around 50 miles (80 kilometers) up, temperatures are a bone-chilling minus 100 degrees Celsius (minus 148 degrees Fahrenheit), and the air is a million times drier than any desert.
Under these extreme conditions, water vapor freezes onto any dust particles floating in the region, seeding the ice crystals that form the tendrils and filaments of noctilucent clouds. Around dusk and dawn, the low-hanging sun brings the clouds to life, making them glow against twilight skies for surface observers.
Volcanoes and Space Dust
Noctilucent clouds were first recorded in 1885 after a volcanic eruption on the Indonesian island of Krakatau, which sent a massive ash cloud into the upper atmosphere that circled Earth for months. Spectacular red sunsets and the distinctive glowing clouds persisted for years.
While such large volcanic eruptions are not all that frequent, nearly a hundred tons of meteoritic dust fall on Earth every day, and this meteor smoke largely seeds the formation of noctilucent clouds.
People living in high latitude areas between 50º and 70º north have the best chance of seeing noctilucent clouds, although over the last century, the unusual sight has been spotted more frequently and much farther south in places such as Utah and Colorado, according to Spaceweather.com. While it's a mystery why the clouds appear to be spreading, some scientists have suggested a link to climate change.
The clouds are also visible from space—astronauts aboard the International Space Station have reported seeing them and have captured the occasional image. Similar clouds were even spotted on Mars back in 2006, when the Mars Express orbiter saw them floating some 60 miles (96.5 kilometers) high. On the red planet, the clouds are likely formed by frozen carbon dioxide.
To catch sight of this beautiful seasonal phenomenon, look toward the northwest when the sun is below your horizon about an hour after local sunset. You can also look for them in the mornings in the northeast about an hour before local sunrise.
Enjoy the show!