The electromagnetic spectrum is a continuous family of waves split into seven main groups. In order from the longest wavelength to the shortest they are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
As you go along the spectrum from radio waves to gamma rays, the wavelength gets shorter and the frequency gets higher. Radio waves have the longest wavelength and the lowest frequency. Gamma rays have the shortest wavelength and the highest frequency. The speed in a vacuum stays constant for every group.
Visible light is the small group we can see. Its colours run from red, which has the longest wavelength, to violet, which has the shortest. Because the groups have no sharp boundaries, they are best seen as one spectrum rather than separate types of wave.
