If you’re up late or rising early this summer, look up and see if you can spot special clouds that glow a blue color on the edge of space.
These clouds, known as noctilucent clouds, occur 50 miles into the atmosphere, which is over 12 times higher than where clouds typically linger. The clouds are seeded by meteors, which means viewers on the ground are essentially seeing condensed meteor smoke. They are illuminated at night by the sun, which is positioned on the other side of the Earth.
The phenomenon is only seen in summertime, and most often occurs at higher latitudes. That’s because the sun is high in the sky at that time of year and shines light over the top of the Earth near the summer solstice illuminating the clouds.
Documented since 1885, the clouds are occurring more often. A century ago they were only observed at latitudes above 50 degrees north (or south), which passes through British Columbia. However, in recent years they have been seen as far south as southern California and New Mexico.
The clouds are too thin to be seen in a daytime sky. They can only be seen when our sky is very dark, such as a few hours before dawn.