An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (30×10[sup]15[/sup] Hz to 30×10[sup]18[/sup] Hz) and energies in the range 124 eV to 124 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it on November 8, 1895.[sup][1][/sup] He named it X-radiation to signify an unknown type of radiation.[sup][2][/sup] Spellings of X-ray(s) in English include the variants x-ray(s), xray(s), and X ray(s).[sup][3] [/sup]