Ordinary sunlight has in it the many colors that we see in a rainbow. They all come to us from the sun in rays. The sun also sends out many "rays" which we cannot see. Some of these "invisible" rays are called infrared radiation.
Infrared rays are given off by anything that is hot. By using special film, it is possible to take a "picture" of a hot electric iron in a darkened room. Infrared rays are a great help in aerial photography. They can pass through clouds and mist better than visible light rays. Infrared cameras are also used for taking pictures of the distant stars.
Infrared rays produce heat when they strike any kind of matter. Some of the warmth we feel from the sun comes from visible light rays, but much of it comes from the infrared radiation. Doctors use infrared rays to produce heat in certain medical treatments. Foods that are broiled are chiefly cooked by infrared rays.
