Polar mesospheric clouds are wispy and elusive. They form 80 to 100 kilometers (50 to 60 miles) above the ground – far higher in the atmosphere than most ordinary clouds. Astronauts aboard the International Space Station (ISS), flying at 350 kilometers (220 miles) up, are ideally placed to observe them. ISS astronauts shot the two photos on this page on August 1, 2014 as ISS flew over the southern Ukraine.
Polar mesospheric clouds typically appear only near Earth’s poles, but during the past few decades they have appeared as far south as Colorado and Virginia. The clouds also have become brighter and thicker. Scientists think the changes are related to long-term climate change, perhaps from increasing water vapor content in the upper atmosphere.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.