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Learn about planets outside our solar system through Exoplanets and Alien Solar Systems by Tahir Yaqoob, Ph.D., a book in our online store book collection.
This is an X-ray image of the Sun taken with the Soft X-Ray Telescope (SXT) on the orbiting Yohkoh satellite. This particular image was taken on November 23, 1999.
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ISAS/Yohkoh team/Lockheed Palo Alto Research Laboratory

X-ray Radiation

X-rays are a high-energy type of electromagnetic (EM) radiation. X-ray radiation has a much shorter wavelength than visible light, so X-ray photons have much higher energies than photons of light.

X-rays lie between ultraviolet "light" and gamma rays on the electromagnetic spectrum. X-rays have wavelengths between about 10 nanometers (10 x 10-9 meters) and 10 picometers (10 x 10-12 meters). X-ray radiation oscillates at rates between about 30 petahertz (PHz or 1015 hertz) and 30 exahertz (EHz or 1018 hertz).

X-rays are subdivided into hard X-rays and soft X-rays. The lower energy soft X-rays have longer wavelengths, while the higher energy hard X-rays have shorter wavelengths. The cutoff between the two types of X-rays is around a wavelength of 100 picometers or an energy level around 10 keV per photon. X-rays with energies between 10 keV and a few hundred keV are considered hard X-rays.

There is no sharp distinction between the highest energy X-rays and the lowest energy gamma rays. The distinction between X-rays and gamma rays is actually based on the origin of the radiation, not on the frequency or wavelength of the electromagnetic waves. Gamma rays are produced by nuclear transitions, while X-rays are the result of accelerating electrons.

X-rays have long been used to "see" through skin and muscle tissue to make medical "X-ray images" of bones when checking for fractures. X-rays that arrive at Earth from space are absorbed by our atmosphere before reaching the ground.

Last modified July 13, 2005 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF