text: The electromagnetic "spectrum" consists of all the different wavelengths and frequencies of electromagnetic waves. All electromagnetic waves travel at the speed of light. Waves can be of high frequency and short wave-length, or of low frequency and long wave-length, or anywhere in between. The reference web site below has a nice sketch showing gamma rays as the highest frequency (shortest wave-length) waves in the spectrum, followed by x-rays with somewhat lower frequency (and somewhat longer wave-length), and ending all the way on the right wtih radio waves with the lowest frequency (and longest wave-length).\n\nIn the middle is the "visible" spectrum, for visible light is an electromagnetic wave, too. Within the visible spectrum, violet light has the highest frequency and the shortest wave-length, and red light has the lowest frequency and the longest wave-length. "Ultra-violet" has frequencies just a little higher than the highest visible violet frequencies, and "infra-red" has frequencies just a little lower than the lowest visible red.