We are bombarded by rays of energy all the time. This is electromagnetic radiation. Your eyes can detect some of these rays, but most of the radiation is invisible. Although some are harmful, all of the rays can be useful to us. They are waves of energy that can travel through space and matter. Electromagnetic radiation comes from the Sun, stars and galaxies, traveling through space to reach us. It can also be made artificially. It consists of electromagnetic waves with a wide range of frequencies and wavelengths.In order of increasing frequency (or decreasing wavelength), some of these are: radio waves, microwaves, infrared rays, light rays, ultraviolet rays, X-rays, and gamma rays. All electromagnetic radiation travels at the speed of light, and the waves or rays can penetrate materials. The complete range of frequencies of electromagnetic radiation is the electromagnetic spectrum. (Dictionary of Science, by Neil Ardley
