Water in the Air
Clouds look fluffy and solid, but they are actually made of billions of tiny water droplets or ice crystals floating in the air. Each droplet is so small and light that air currents keep it floating — like dust motes drifting in a sunbeam.
But where does all that water come from? It starts at the surface. The sun heats water in oceans, lakes, rivers, and even puddles, causing water molecules to escape into the air as an invisible gas called water vapor. This process is called evaporation.
Plants release water vapor too, through their leaves, in a process called transpiration. A single large oak tree can release over 40,000 gallons of water vapor in a year!
You cannot see water vapor — it is invisible. But the air around you is full of it. On a humid summer day, the air feels heavy and sticky because it contains a lot of water vapor.
**Think About It:** When you breathe out on a cold day and see your breath, you are seeing water vapor from your lungs condensing into tiny visible droplets — you are making a tiny cloud!