Book excerpt: Clouds are simple enough, just a collection of ice crystals or water droplets visible to everyone. Yet they are a source of endless wonder. They appear in an infinite number of shapes and forms. Some are beautiful, some awe inspiring, and some, like the whirling funnel cloud, are terrifying. Clouds inspire artists, poets, songwriters. They have reminded astronauts, looking down from space, that Earth, a seemingly abstract orb, is a place of life and movement. those great swirls of white-as they change shape, swell, evaporate into wisps, disappear and come back, glow with sunlight or darken with rain-are a constant reminder of how dynamic our planet is.