The Highest Clouds
Noctilucent clouds (NLCs) are the highest clouds in the sky. These shimmering, iridescent clouds appear at late twilight when the sun strikes water crystals in the upper atmosphere.
Amazing But True!
- Noctilucent are part of the polar mesospheric clouds of the upper atmosphere, appearing at 83 km above the surface.
- Noctilucent clouds appear near the polar regions in summer: November through February over Antarctica and May through August over the Arctic.
- Methane concentrations in the atmosphere have doubled in the past century, and may be spurring on NLC formation.
Show What You Know
With the links below, learn more about noctilucent clouds. Then answer the following questions.
- ScienceAtNASA, ScienceCasts: Electric-Blue Clouds Appear Over Antarctica (video): http://www.youtube.com/watch?v=GHpxD807kM4
- APOD, NASA, Noctilucent Clouds and Aurora Over Scotland (video, just for enjoying the beautiful sky): http://apod.nasa.gov/apod/ap130819.html
- When and after what event were noctilucent clouds first noticed?
- What is the relationship between the event mentioned in #1 above and the appearance of notilucent clouds?
- Why do NLCs appear in the summer, but not at other times of year?
- How has the appearance of NLCs changed since they were first viewed?
- What is the relationship between NLCs and global warming?