Noctilucent Clouds

atmosphere · rare sky phenomenon · ice crystals · summer

Clouds that glow at night. Noctilucent clouds are so high in the atmosphere that they catch sunlight even after the sun sets below the horizon, making them shine like ghostly ribbons across the twilight sky.

Made of ice crystals. These clouds are formed entirely from tiny ice crystals floating at the very top of Earth's atmosphere, about 50 miles up, where it's incredibly cold.

Only visible in summer. You can only see noctilucent clouds during summer months from high latitudes (far north or south), and only during the twilight hours when the light is just right.

Named for their glow. The word 'noctilucent' comes from Latin and means 'night shining' because they literally appear to shine in the darkness of night.

Connected to pollution. Recent scientists think that increased methane in the atmosphere may create more of these clouds, as methane breaks down high up and forms extra water vapor.