Why are silvery clouds blue?

Alan Dyer photographed these silvery clouds on June 16 at Gleichen in Alberta, USA. The author of the photo said that he had rarely observed such bright silvery clouds — they glittered and glowed electric blue.

These are the highest clouds on Earth. They appear when in the summer water vapor, which has risen to the edge of space (to a height of about 83 km), crystallizes around meteorite particles, as many researchers believe. When you see them, you are literally watching frozen meteor clouds.

But why are they blue? The answer is ozone. Research conducted in the 1970s showed that most of the light falling on silvery clouds first passes through the ozone layer of the planet. Ozone absorbs longer light waves (red), allowing shorter ones (blue) to pass through. This is what gives these beautiful clouds their color.