Clouds

Drops. That’s all there is to clouds — they’re made from countless water drops too small to see with the naked eye. The atmosphere is actually full of these drops, which scientists call water vapor. As the drops rise, they cool and stick to things like dust, ice, sea salt, even pollution, creating clouds. The vapors take on all manner of shapes — and we don’t mean hearts or mythical beasts, or whatever else people imagine seeing. The American Meteorological Society, official chronicler of clouds, lists 10 cloud genera, 14 species and nine varieties. The strangest of these may be Earth’s highest, at 250,000 feet or more: thin, wispy noctilucent clouds (left), visible only at twilight.