Early, on clear mornings, beads of water often appear on pieces of grass, leaves or the tops of cars. That is called dew . When air close to the ground cools to the place where it cannot hold all its water vapor it becomes dew. When the excess water vapor changes to liquid on objects near the ground it is called dew drops.
Objects absorb heat from the sun during the day. Thermal radiation is a process that, at night, objects lose heat. As objects near the ground cool, the temperature around them do, too. Warmer air can hold more water vapor than colder air can. If the air continues to cool, it will eventually reach the dew point. The temperature at which the air contains as much water vapor as it can hold is the dew point. Dew forms better when the humidity is high.
Dew has a purpose, too. The purpose of dew is it gives moisture to plants and soil. Dew is not like rain but does pretty much the same job just with less water. Dew can also turn into frost if the temperature is 32 degrees F or below. Click here to get some info on fog.