Infrared rays, rays resembling light rays, but undetectable by the human eye. Also called heat rays, infrared rays are given off by objects in relation to their temperature. Emission of infrared rays increases as an object gets hotter. The British astronomer Sir William Herschel discovered infrared rays in 1800 by observing the effect of the heat they produced. The sniperscope is an instrument that perceives infrared rays from objects that are warmer than their surroundings. The military utilizes infrared radiation and the sniperscope in missile detection, guidance systems, and night-vision apparatus.
See also: Electromagnetic waves.