Infrared radiation, or infrared light, is a type of radiant energy that is invisible to the human eye but can be felt as heat. It is part of the electromagnetic spectrum, which includes gamma-rays, X-rays, ultraviolet radiation, visible light, infrared radiation, microwaves, and radio waves. Infrared radiation has a longer wavelength than visible light but shorter than radio waves. It is usually divided into three regions: near-infrared, middle-infrared, and far-infrared, based on wavelength. Infrared radiation is emitted by all objects in the universe, but two of the most obvious sources are the sun and fire. Infrared radiation has a variety of uses and applications, including heat sensors, thermal imaging, night vision equipment, and fiber optic cables. Infrared astronomy uses sensor-equipped telescopes to observe objects in space that the human eye cant detect, such as molecular clouds, stars, planets, and active galaxies.