1. The emission and propagation of radiation associated with a periodically varying electric and magnetic field traveling at the speed of light.

Types include gamma radiation, X-rays, ultraviolet, visible, and infrared radiation, and radar and radio waves.

2. Radiation that is produced with a combination of magnetic and electric forces.

It exists as a continuous spectrum of radiation, from that with the highest energy level and the shortest wavelength (gamma rays) to that with the lowest energy and longest wavelength (long radio waves).

All forms of electromagnetic radiation travel at the speed of light.

Light, radio waves, and X-rays are forms of electromagnetic radiation. Almost all of our knowledge of extraterrestrial objects comes from emitted or reflected electromagnetic radiation (visible light or radio waves).