Bill Hinshaw, age 12, of Germantown, Tenn., for his question:

WHAT IS DEW POINT?

Dew point is the temperature at which moisture in the air begins to condense.

When the relative humidity is 100 percent, the dew point is either lower than the air temperature or the same as the air temperature.

Dew forms when a thin film of air, in contact with the surface, is cooled to below the dew point. Cooling the air below its dew point causes dew on the surface or fog in the air, when the dew point is above the freezing temperature.

If the air temperature and dew point are below freezing, frost may form on the surface, or ice crystals may form in the air. Fog and clouds occur when large volumes of air are cooled to below the dew point.