Radio waves are at the long-wavelength end of the electromagnetic spectrum, as long as hundreds of meters down to a millimeter and well-known "microwaves" have wavelengths of around a few centimeters. As wavelength decreases we find infrared (1R) radiation, commonly experienced as heat, then light waves which range from 70 millionths of a centimeter (7 x 10-5 cm) for the long wavelength red light down to 40 millionths of a centimeter (4 x 10"5 cm) tor violet light. The colors of the rainbow fall between these two extremes. Beyond that going to shorter wavelengths comes ultraviolet (UV) radiation, sometimes called "blacklight." (UV causes sunburn, and in large doses is extremely harmful to living organisms.) Next are Xays, with wavelengths so short that they literally wriggle between atoms and so can penetrate our bodies. Finally, at the shortest (less than 1 x IO8 cm) wavelength end of the spectrum are the gamma rays.
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