Cirrus clouds are the ones with feathery tails, and their presence often adds a delicate beauty to the sky. They are very high clouds, usually 20,000 to 30,000 feet above the ground, where the temperature is well below freezing. Even in summer, these clouds are made up entirely of snowflakes, which is why they look wispy and feathery.
Sometimes, cirrus clouds have tails that hang earthward. This is high-altitude snow falling from the cloud. We don’t get precipitation from cirrus clouds because they are so high that these snowflakes always sublimate (turn back into water vapor) in drier air on the way down.
Although much of the truly spectacular colors and shapes of clouds at sunrise and sunset are made of lower cumulus or altostratus clouds, the presence of cirrus clouds at sunset can add an extra layer, creating an extra dimension in the side-lit display when the sun is low.