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| Description: Heat may also be transferred through electromagnetic radiation. This transfer of heat, Hr, is often called simply radiation. All objects above absolute zero, (–273°C), give off electromagnetic radiation, but the most obvious source in our environment is the sun. Curiously, we are blind to most of this because at sea level over half of the energy content of sunlight falls outside our visible range. Much of this radiation that we cannot see is in the infrared part of the spectrum. The electromagnetic radiation emitted by most objects in our environment, including our own bodies, is also infrared light. Infrared light is responsible for most of the warmth you feel when standing in front of a fire or that you feel radiating from the sunny side of a building on a winter's day. The chilling effect of standing outdoors under a clear, cold night sky with no wind is also mainly due to radiative heat flux, in this case from your body to the surroundings, including the night sky.
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