Science and Space

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High-energy gamma rays from Earth's atmosphere

Scientists using NASA's High Energy Solar Spectroscopic Imager satellite said they have observed a source of high-energy gamma rays that originate on Earth's upper atmosphere, not from outer space. They are very short blasts of gamma rays, lasting about one-thousandth of a second and emitted into space by electrons traveling at 99.99 percent of the speed of light. Originally discovered in 1994, the origin of terrestrial gamma-ray flashes (TGFs) has remained a mystery. The best guess at present is they are generated by the build-up of electrical charges at the tops of thunder clouds due to lightning discharges. TGFs have been correlated with lightning strikes, the scientists said.

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