A cloud is formed from a mass of minute water droplets ( or ice cristals) suspended in the air. These droplets move downwards very slowly because of their very slight volumetric mass and the air resistance, so that the slightest upward air current is enough to keep them stationary or make them rise ; that is why clouds seem to "float" in the atmosphere.
The cloud's appearance depends on how much light it receives, but also on the type, size and number of particles which make it up, and their distribution in space.
These particles evaporate, sublimatew (to pass from the solid state to a gas), precipitate and reform themselves unceasingly, so we should not think of clouds as "unyealding blocks" but as systems in constant flux. ...........................................................................................................
