Encyclopedia > Rain

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Rain is a form of precipitation, as is snow, sleet, hail, dew or fog. Rain forms when separate drops of water fall to the Earth's surface from clouds. Not all rain reaches the surface, however; some evaporates while falling through dry air, a type of precipitation called virga.

Rain plays a major role in the water cycle[?] in which moisture[?] from the oceans evaporates, condenses into clouds, precipitates back to earth, and eventually returns to the ocean via streams and rivers to repeat the cycle again.

The amount of rainfall is measured using a rain gauge. It is expressed as the depth of water that collects on a flat surface, and is measured to the nearest 0.25mm.

Falling raindrops are often described as "tear-shaped", round at the bottom and narrowing towards the top, but this is incorrect. Small raindrops look almost like spheres, while larger ones look like spheres whose bottom has been flattened, like a hamburger bun. Even bigger ones can assume a parachute-like shape. The larger ones fall faster.

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