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The Universe at Your Fingertips 2.0 DVD from the Astronomical Society of the Pacific is in our online store, filled with Earth and space science resources.
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.
Click on image for full size
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 is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA