TUESDAY, JULY 18 - OFFICIAL TEMPERATURES IN THE SHADE


When you hear a temperature reported on TV, it's often an "official" reading taken at a nearby weather observing station. At these stations, the thermometers are shielded from sunshine inside specially-constructed shelters that allow air in, but not direct sunlight.

This may sound like a lot of trouble to go through, but it's necessary if you want to accurately measure the temperature of the air. If a thermometer sits out in the sun, the thermometer itself - the glass, the liquid inside - will absorb sunlight, and heat up. You wouldn't be measuring the temperature of the air anymore, but rather the temperature of the heated-up thermometer. On a sunny day, that can easily be 30 degrees higher than the actual air temperature.

So the next time you hear a temperature of 80 degrees reported on the radio but your backyard thermometer reads 115, you'll know the reason for the big difference.

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