Daniel Coleman, age 12, of Camden, N.J., for his question:

WHAT CAUSES DEW?

Dew is the moisture that you find has condensed during the night on cool surfaces, such as leaves or grass. The leaves had been warmed by the sun during the day. As the cool night air hits, dew sometimes forms.

Warm air usually holds more water vapor than cold air. The moisture laden warm air, coming in contact with the leaves or grass, is cooled to a temperature at which its moisture condenses and can be seen as dew.

Other sources of moisture that form dew are the warm earth, from which vapor rises, and plants, which discharge vapor.

You'll find more dew builds up on clear, still nights than on windy ones. Windy nights keep the warm sir in motion.

On cloudy nights the surface does not usually cool enough to cause condensation of moisture. On nights when 1t is below freezing, the dew crystals form frost.