Mist is tiny droplets of water hanging in the air. These droplets form when warmer water in the air is rapidly cooled, causing it to change from invisible gas to tiny visible water droplets.

Mist often forms when warmer air over water suddenly encounters the cooler surface of land. However, mist can also form when warm air from land suddenly encounters cooler air over the ocean. This is the cause of the summer fog in San Francisco, California. You can even create mist yourself, as you probably know, when you exhale the warm air from your body into the cold air.

Mist is a lot like its cousin, fog. The difference between the two depends on how well you can see. Mist is less dense than fog. If you can't see beyond one kilometer (two-thirds of a mile) in front of you, it's fog that's clouding your vision. If you can see more than that, it's just mist.

Mist caused by volcanic activity is simply hot water vapor expelled along with gases and, sometimes, lava, by a volcano. Volcanic mists are emitted by steam vents, or cracks in the Earth's surface around volcanoes and geysers. Sometimes, volcanic mists are watery clouds you can walk through. Steam vents are popular tourist attractions at Volcanoes National Park in the U.S. state of Hawaii, for example.

Sometimes, however, these volcanic mists have other chemicals in them, often causing distinct odors. Volcanologists study the chemical properties of these mists to see what rocks and gases are under the volcano. They also measure the temperature. The hotter the steam, the more likely the volcano is to erupt. A difference of only a few degrees can mean the difference between a nice mist and a steam explosion.

You'll find mist all over the world. Some of the world's most famous foggy spots, such as Scotland, in the United Kingdom, are also home to mist. Scotch mist, in fact, is a very light, steady drizzle of rain.