How is the dewpoint determined?

Answer 1

Hello,
I was a weather observer in the Air Force in the 70's. We measured dew point thuslyl.

We had two thermometers that were joined together. On one thermometer we had a "wick" which we would dampen with water. Then we would spin both thermometers. The dew point was the temperature produced by the evaporating water on the "wicked" thermometer. The more the water evaporated the greater the difference between the two temperatures called the "wet bulb" and the "dry bulb".

Answer 2

Relative humidity is measured with an instrument called an hygrometer and the simplest hygrometer is the sling psychrometer described by another answerer. When the temperature on the wet bulb does not decrease any more after whirling the psychrometer in the air for a specified amount of time, it is recorded as the dew point temperature.

Answer 3

The simple answer--

The given temperature at which due will form on the ground.

Generally speaking in hot humid climates due points will be up pover 70 at times, but in the desert they can be extremely low relative to the current temp.