Rain is a common phenomenon in most parts of the world, save those that are very hot and very dry. Scientifically speaking it’s the falling of precipitation from the sky in the form of water droplets; in layman’s terms, rain is water from the heavens. Most of us have seen at least a few splashes of rain in our lifetime.
But what is rain? What causes it? How does water from the ground get up into the sky and come falling back down again? It’s pretty simple, actually, and it begins with something know as the water cycle.
The water cycle begins on a warm day somewhere on the planet. The sun, shining down on all sorts of sources of water – ponds, stream, lakes, oceans, even ice and snow – causes that water to turn from a liquid into a gas. This process is known as evaporation, and when the water is evaporated it’s released into the air.
Hot air rises above cool air, and so the water vapor, a gas, is carried up into the sky. Though this air is warm, however, it won’t stay that way, as the higher it goes the cooler the air around it gets. When this happens the water vapor begins to cool, and as it does it starts to turn back into a liquid. This process, the reverse of evaporation, is known as condensation.
Depending on how high the water vapor got before it began to change back, it will either transform into water droplets or ice crystals. This changed water, when brought together in large bunches, creates what’s probably sitting over your head right now: clouds. Clouds are nothing more than condensed water floating in the sky, still not ready to fall back down.
That doesn’t last forever, though. When there’s enough water in these clouds the air becomes saturated, and can no longer hold any water. When this happens the water begins to fall down from the clouds as rain drops. This will only happen if the clouds are in a warm weather region; if the sky is cold enough, sleet, hail and even snow may fall instead. (It’s also possible for the sky to become warm enough that the water is changed back into a gas and the clouds disappear, though don’t be fooled – the water is still up there, and may form another cloud if given a chance.)
Once the rain falls it will gather in pools or return to sources of water, and once it does the process will begin again. The water cycle is never ending, and thus neither is the rain.