![]() ![]() It was long known that fires emit invisible heat in 1681 the pioneering experimenter Edme Mariotte showed that glass, though transparent to sunlight, obstructed radiant heat. As a form of electromagnetic radiation, IR propagates energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon. Almost all black-body radiation from objects near room temperature is at infrared wavelengths. Longer IR wavelengths (30 μm-100 μm) are sometimes included as part of the terahertz radiation range. IR is generally understood to encompass wavelengths from around 1 millimeter (300 GHz) to the nominal red edge of the visible spectrum, around 700 nanometers (430 THz). It is therefore invisible to the human eye. Infrared (sometimes called infrared light and IR) is electromagnetic radiation (EMR) with wavelengths longer than those of visible light and shorter than radio waves. This false-color infrared space telescope image has blue, green and red corresponding to 3.4, 4.6, and 12 μm wavelengths, respectively. ![]()
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