Thermometer in the Sun

Most recent answer: 02/16/2013

Q:
Sir, if the thermometer is placed in direct sunlight,will it be read the temp. of sun or air or something else???
- Aqib (age 18)
Karachi,PAK
A:
It will definitely not reach the temperature of the sun. An object completely surrounded by things that glowed like the sun would reach the temperature of the sun's surface, but we are not surrounded by the sun. It occupies only a little piece of the sky. If an object can soak up energy from sunlight and then lose it by only sending off its own (infrared) light, it would end up only somewhat hotter than the earth's surface. That's what happens to the earth's surface itself, but since half the time is spent at night, it doesn't get as hot as that thermometer would in the day.  Since the thermometer can also lose heat to the nearby air, it will end up somewhat hotter than the nearby air, very much like other things that you touch that have been left in the sunlight. Exactly how much hotter depends on details, like how shiny the thermometer is and how much breeze is blowing.

Mike W.

(published on 02/16/2013)