Infrared radiation (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light. Infrared radiation is emitted or absorbed by molecules when they change their rotational-vibrational movements. The name “infrared” refers to red color, the lowest wavelength of visible light.
IR spectroscopy is used to study and identify molecules by their unique absorption patterns. Thermal imaging allows us to see heat sources in complete darkness and can be used for medical diagnosis, military targeting, and search and rescue missions. IR astronomy uses telescopes that detect IR emissions from astronomical objects in order to learn about their physical properties, composition, and motions through space.
All matter emits IR as a function of its temperature; the hotter an object is, the more IR it emits. The Sun, at a surface temperature of approximately 5500 K (~5000°C), emits most of its radiation in the visible spectrum but also emits significant amounts of IR. Our atmosphere absorbs some incoming solar IR before it reaches Earth’s surface; this greenhouse effect keeps our planet warm enough to support life.
Most objects in our everyday lives emit very little IR; however there are some exceptions like hot coffee or a burning candle. Night vision goggles detect the small amounts of IR emitted by people and animals in complete darkness and allow us to see them clearly.