Dew point

The dew point is the temperature that air, of a constant absolute humidity and pressure, must be cooled to in order for the relative humidity to rise to 100%. This temperature is a thermodynamic property that depends on the pressure and water content of the air. When the air at a temperature above the dew point is cooled, its moisture capacity is reduced, and when the temperature passes below the dew point water vapor will condense, or precipitate, to form liquid water. When this occurs through the air’s contact with a colder surface, the precipitate on that surface is dew.