This is an infrared (IR) view of Mt. Jian in Japan erupting in 1983. IR "light" is a form of electromagnetic radiation given off by hot materials like lava. Click on image for full size (44K JPEG) Image courtesy Daedalus Enterprises, Inc., in Ann Arbor, Michigan.

Electromagnetic radiation is the result of oscillating electric and magnetic fields. The wave of energy generated by such vibrations moves through space at the speed of light. And well it should... for visible light is indeed one form of electromagnetic (EM) radiation.

X-rays, radio waves, gamma rays, and infrared and ultraviolet "light" are the other main types of electromagnetic radiation. They are all traveling vibrations of electromagnetic waves, each with its own characteristic wavelength. Organized in order of wavelength, they make up the electromagnetic spectrum.

Sometimes it is useful to think about electromagnetic radiation as though it came in packets. These packets of EM radiation are called "photons".

There is a second main type of radiation, which is the result of subatomic particles moving at very high speeds. That type of radiation is called "particle radiation".