Since their discovery in 1895, X rays have proved a vital tool of science, making it possible to examine previously hidden worlds ranging from the tiniest of atoms to the most distant galaxies in space. Their usefulness lies in their ability to penetrate matter.
X rays owe their penetrating power to their relatively short wavelengths and high energy.
The wavelengths of X rays range from about 0.05 angstrom to hundreds of angstrom units. The shorter the wavelength and the higher the energy of an X ray, the deeper it penetrates matter. Visible light, by contrast, has much longer wavelengths and lower energy. One of the earliest applications of X rays was in medicine, where they were used for both diagnosis and therapy. Today X rays are still most widely used in this field.