MANY FORMS

The discovery of EM fields led ultimately to the variety of wireless communications systems we know today. Radio waves are not the only form of EM radiation. As the frequency increases above that of conventional radio, we encounter new forms. First comes microwaves. Then comes infrared (IR) or “heat rays.” After that comes visible light, ultraviolet (UV) radiation, x-rays, and gamma (γ) rays.
In the opposite, and less commonly imagined, sense, EM fields can exist at frequencies far below those of radio signals. In theory, an EM wave can go through one complete cycle every hour, day, year, thousand years, or million years. Some astronomers suspect that stars and galaxies generate EM fields with periods of years, centuries, or millennia.