Humidity is the amount of water vapor that is in the air. Water vapor is the gas state of water. Humidity comes from water evaporating from lakes and oceans.
A hygrometer is a meteorological instrument used to measure the humidity of the air. Back in the 18th century, people measured humidity with hair curls! Early hygrometers used a hair with a weight attached to it to measure how much the hair shortened due to moisture absorption. Moist hair tends to curl and shorten.
Warmer water evaporates more quickly, that’s why the most humid regions on Earth are close to warm bodies of water. Air can hold different amounts of water depending on the temperature. Deserts usually have low humidity, and tropical regions have high humidity.
Humid air feels damp, and kind of stuffy. The higher the humidity, the less effective your body’s cooling system of “sweating” works, since the sweat on your skin won’t be able to evaporate! Compared to hot, + dry climates, the human body doesn’t do nearly as well in hot + humid climates because our sweat simply can’t cool us down. Interestingly, insects thrive in regions with high humidity because it decreases dehydration, thus increasing their survival.
Relative humidity tells us how much water vapor is in the air versus how much it can hold. This is what we hear about on the news, as a percentage. It let’s us know how much water vapor the air is holding, compared to how much it could hold, on any given day. People are usually most comfortable at a 45-percent relative humidity.
The dew point is the temperature where water vapor condenses back into liquid water. All air holds different amounts of water vapor. The dew point can show us the amount of moisture in the air. The higher the dew point, the higher the humidity.
You can even detect smells better in humid air because moisture helps smells travel. Think about how smelly a wet dog is compared to a dry one!