cloud
A cloud is a collection of tiny drops of water or ice grains floating in the atmosphere of Earth, planet or satellite. (The part that looks like a cloud between stars is called a 'nebula', which is a collection of interstellar matter.) The meteorological field that studies clouds is called 'cloud science' do. Clouds on the earth are mostly generated from water vapor. The radii of the grains are about 0.02 ~ 0.05mm, and when several tens of millions of small droplets gather, they can be observed as clouds. Because the dark cloud has a reflectivity approaching 70% to 95%, the top of the cloud looks white. But the droplets in the clouds scatter the light, so they become gray as they go down. In addition, the color changes depending on the sunlight and the surrounding environment. Clouds absorb infrared rays strongly. Weather phenomena such as precipitation are also caused by clouds.