Condensation is what happens when a gas cools down and turns into liquid. You see it every time a cold glass of lemonade sits on the counter on a hot day: tiny water droplets form on the outside of the glass. Those drops aren't leaking through the glass. They're water vapor from the air that touched the cold surface, cooled down, and turned back into liquid water.

The same process creates morning dew on grass, frost on windows, and clouds in the sky. When warm, moist air rises and cools high in the atmosphere, the water vapor condenses into tiny droplets that form clouds. When you breathe on a cold mirror, your warm breath hits the cool surface and condenses instantly, fogging it up.

Understanding condensation helps explain everyday mysteries: why bathroom mirrors steam up during showers, why car windows fog up on cold mornings, and why you can see your breath on winter days. The water was always there in the air as invisible vapor. Condensation just makes it visible by turning it back into liquid.

The opposite of condensation is evaporation, when liquid water heats up and turns into invisible water vapor. Together, these two processes drive the water cycle that moves water endlessly between the earth, air, and sky.