The emission of radiant energy as particles or
waves such as heat, light, alpha particles, and beta particles.
Heat transfer by infrared rays is also known as radiation or
radiative heat transfer. Infrared radiation travels at the speed
of light and can travel through a vacuum, gets reflected and
refracted, and does not affect the medium that it passes
through.
The electromagnetic spectrum divides types of radiation
according to wavelength, with the shortest wavelengths being
cosmic rays, and in increasing wavelength, gamma rays, X
rays, ultraviolet rays, visible rays, infrared rays, microwave
rays, radio waves, and television waves. The environment
contains a low level of background radiation that is always
present, most being given off from radioactive decay of minerals
and radioactive gases such as radon and thoron. Some
background radiation also comes from space and is known as
cosmic radiation. The Sun emits solar radiation consisting of
visible light, ultraviolet radiation, and infrared waves spanning
the entire spectrum of electromagnetic wavelengths from
radio waves to X rays. The sun also emits high-energy particles
such as electrons, especially from solar flares. Shortwavelength
high-frequency electromagnetic waves from
0.0000157 to almost 0.0 inch (400–4 nanometers) are
known as ultraviolet radiation, which is powerful and needed
by humans but harmful in strong doses. X rays, because of
their very wavelength, are able to penetrate soft tissue, some
sands and soils, and reflect off internal denser material such
as bones or rocks. This property has made X rays useful for
medical practices and geologic mapping of subsurface materials.
Visible radiation includes all that humans see with their
eyes, including the wide range of colors of the rainbow.
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