Dear Tom,
It’s much warmer in the sun than in the shade, and I have always wondered how temperature readings are determined. Is the temperature an average of the sun and shade temperatures?
— Mary Braun
Dear Mary,
Chicago’s official temperature is provided by a shaded sensor located well away from runways at O’Hare International Airport. The instrument is a hygrothermometer, equipment that measures both air temperature and moisture content. The sensors are mounted six feet above the ground in a white louvered enclosure that shields them from precipitation and direct sunlight. It is ventilated so that it provides the “free air” temperature. By international agreement, readings are taken at that height to provide consistency in the temperature data.
