Fair weather cumulus clouds look like big, fluffy cotton balls floating in the sky. Cirrus clouds are thin and wispy. Because they look so insubstantial, most of us don't think about how heavy clouds actually are. The truth is, they're very heavy. The average fluffy cumulus cloud weighs about 500,000 pounds (226,700 kg). Storm clouds are much heavier, since they're weighed down by water.
This becomes a little easier to visualize when one remembers that clouds are made of water droplets. If you think about how quickly you tire of carrying just a gallon of water, the weight of clouds becomes much easier to understand. These droplets are sometimes microscopic, and are usually spread out across many, many miles, which is how they stay in the air and don't come crashing to the ground.
Humans have always been fascinated by clouds. References to clouds appear in the Upanishads, from 3,000 B.C., while Aristotle waxed eloquent about them in "Meteorology," his work of 350 B.C.
- The average cloud droplet is 0.0008 inches (.02 mm) in diameter, some five times smaller than the thickness of a sheet of paper.
- Every planet with an atmosphere has clouds, whether they're made of water droplets, as on Earth, or made of ammonia, as on Saturn.
- The cloudiest places on Earth are the Prince Edward Islands, off the coast of South Africa. Parts of these islands see less than 800 hours of sunshine per year.