"Electric blue" clouds appeared over St. Petersburg

On July 19, residents of St. Petersburg could watch one of the most amazing natural phenomena — silver clouds almost all night.

Silvery clouds are the highest clouds on Earth. These are very cold, extremely sparse and filled with tiny ice crystals clouds hovering at an altitude of about 80 kilometers above the surface of the planet. When the sun's rays pass through these ice crystals, the clouds acquire a rich blue color, clearly visible in the deep twilight.

Observers of silvery clouds often describe their color as "glowing electric blue". Why do they look like that?

First, they consist of tiny ice crystals the size of particles in cigarette smoke, which looks blue for the same reason — tiny particles scatter blue light better than other colors.

Secondly, studies conducted in the 1970s showed that sunlight falling on silvery clouds first passes through the ozone layer of the Earth, and ozone tends to scatter red light, passing blue.