Dew Point

dew point: see dew.

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dew point [′dü ‚pȯint]

(chemistry)

The temperature and pressure at which a gas begins to condense to a liquid.

(meteorology)

The temperature at which air becomes saturated when cooled without addition of moisture or change of pressure; any further cooling causes condensation. Also known as dew-point temperature.

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Dew Point 

the temperature at which air becomes saturated by water vapor when cooled at a given moisture content and a constant pressure. The condensation of water vapor begins when the dew point is reached in the air or on objects in contact with the air.

The dew point is one of the major characteristics of humidity and can be calculated from the temperature and humidity of the air or determined directly with a condensation hygrometer. If the relative humidity is less than 100 percent, the dew point is always less than the actual air temperature. The dew point decreases with decreasing relative humidity.

At saturation, that is, at a relative humidity of 100 percent, the actual temperature coincides with the dew point. Thus, at a temperature of 15°C, the relative humidities of 100, 80, 60, and 40 percent correspond to the dew points of 15.0°, 11.6°, 7.3°, and 1.5°C, respectively.