A very energetic wavelength, or frequency, of light. X-rays are more energetic than ultraviolet light, but less energetic than gamma-ray. They range in wavelength from 10^-8 meters to 10^-12 meters, and in frequency from 10^17 to 10^20 Hz. X-rays can be quite harmful to life because they are strong enough to ionize atoms and thus destroy cells. The Earth's atmosphere shields us from all astronomical x-ray radiation. X-rays produced by people do have useful applications, however; for example, they are used to help identify broken bones and to treat certain types of cancer.