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How X-rays Were Discovered
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X-rays were first observed and documented in
1895 by Wilhelm
Conrad Röntgen, a German scientist who found them quite by accident
when experimenting with vacuum tubes. A week later, he took an X-ray
photograph of his wife's hand which clearly revealed her wedding ring
and her bones. The photograph electrified the general public and aroused
great scientific interest in the new form of radiation.
Röntgen called it "X" to indicate it was an unknown type of radiation.
The name stuck, although (over Röntgen's objections), many of his
colleagues suggested calling them Röntgen rays. They are still
occasionally referred to as Röntgen rays in German-speaking countries.
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Mrs. Röntgen's hand, the first X-ray
picture of the human body ever taken.
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In June 1990, the United States launched a new
German-built satellite
to record X-rays from the sky. This joint U.S./German/U.K. program was
named Röntgen Satellite in his honor (though it is almost always
referred to as ROSAT).
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How Astronomers Observe X-rays Emitted by Cosmic
Sources
Although the more energetic X-rays
(E > 30 keV) can penetrate the air at least for distances of a few meters
(Röntgen
would never have observed them if they could not, and medical X-ray machines
would not work), the Earth's atmosphere
is thick enough that virtually none are able to penetrate from outer space all
the way to the Earth's surface. X-rays in the 0.5 - 5 keV range,
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