What are clouds made of?

01.04.2015 |

Episode #6 of the course “Science questions everyone should know how to answer”

This seemingly simple question actually has an entire branch of physics devoted to it called cloud physics. Of course, scientists already know what clouds are made of, but there are still so many other questions to study within the same realm.

As for our question, clouds are made from water that has changed from liquid to gas and then back to liquid. When the sun shines over rivers, lakes, and the ocean, it heats up the surface of the water. Once at a certain temperature, water changes from liquid to water vapor and rises into the air. This is called evaporation. As the water vapor rises, it begins to cool down and turn back into condensed water droplets. This moment is called the dew point.

These tiny droplets of water hang suspended in the Earth’s atmosphere. Groupings of these tiny droplets are called clouds. The more water droplets a cloud accumulates, the bigger and heavier they grow. At a certain point, the water releases from the clouds and gravity brings it back down to Earth, refilling the rivers, lakes, and oceans from which it left.

A good way to tell which clouds have a lot of water droplets in them is to notice their color. In addition to becoming bigger and heavier, clouds also become dark and grey as they accumulate more droplets. This is not because water is grey, but because that many molecules bunched together don’t allow sunlight to pass through them, making them appear dark. White clouds contain very few water droplets, thus creating space for sunlight to pass through and make them appear white.


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