The electromagnetic spectrum is made up of all electromagnetic radiation, including photons with a wavelength ranging from atomic diameter to the width of the earth. It has three basic properties: frequency or wavelength, intensity, and polarization. Humans can only see a small fraction of it, with the acronym ROYGBIV used to describe visible colors. Infrared, microwaves, and radio waves have longer wavelengths, while ultraviolet, X-rays, and gamma rays have shorter wavelengths. All electromagnetic radiation travels at the speed of light and is primarily sourced from the sun.
The electromagnetic spectrum consists of the totality of all electromagnetic radiation. Made up of photons, everything in the electromagnetic spectrum is sometimes referred to as light, although the word sometimes refers only to the human-visible portion of the electromagnetic spectrum.
Photons have some characteristics of a particle and some of a wave. For example, they have a wavelength. The wavelength of a photon ranges from many times smaller than an atomic diameter to the width of the earth. All radiation that is part of the electromagnetic spectrum has three basic properties: frequency or wavelength, intensity, and polarization. The last property, which refers to the angle of the electromagnetic wave, cannot be detected by the human eye, although bees can perceive it.
All electromagnetic radiation travels at the speed of light, even if an interposed material of the right composition can reflect it, slow it down or absorb it. The primary source of electromagnetic spectrum radiation on earth is from the sun, although many processes can create it, including various phosphorescent life forms.
Electromagnetism can be thought of as an oscillating perturbation in the electromagnetic field. The electromagnetic spectrum consists of all possible perturbations. We can only see a small fraction of it: light with a wavelength between about 400 nanometers and about 750 nanometers. Perhaps not surprisingly, this is the wavelength of light that pours in large quantities from the sun, and our visual systems have evolved to perceive it. The acronym ROYGBIV is sometimes used to describe the human-visible colors of the electromagnetic spectrum, in order from lowest to highest frequency: red, orange, yellow, green, blue, indigo, and violet.
The type of electromagnetic radiation with a wavelength longer than that of the color red is called infrared, and is emitted by all objects that give off heat. Infrared ranges in wavelength from about 750 nanometers down to one millimeter. Following infrared are microwaves, with wavelengths ranging from about one millimeter to about 30 centimeters (12 inches). These are used in a microwave oven. Radio waves include anything with a wavelength longer than microwaves. These have the greatest ability to penetrate the earth’s atmosphere and hence are extremely important for communications technology.
Electromagnetic radiation with shorter wavelengths than visible light includes ultraviolet, followed by X-rays, then gamma rays. Gamma rays are a type of cosmic ray and can have extremely high energies. Gamma rays can have much higher energies than anything produced in our particle accelerators, and their wavelengths can be as small as a single subatomic particle.
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