Radio waves, for instance, have frequencies that range from fewer than a hundred oscillations per second to up to around three million. The term microwave covers a range from there up to three hundred billion. Infrared sits between microwaves and visible light. When frequencies are greater than that of blue light, they are ultraviolet rays. Then comes X-rays, and oscillating up and down over a hundred billion billion times per second are gamma rays. The entire range, from radio waves to gamma rays, is called the electromagnetic spectrum.
