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| | Searching for gamma rays under dark desert skies |
 | | During the day, the solar facility's 220 heliostats, which are essentially adjustable mirrors, focus the light of the sun onto a 200-foot central tower, and this intense beam of visible light is used in solar energy research. |
 | | Because they are traveling faster than light, they generate the visual equivalent of a sonic boom, a faint blue glow, called Cherenkov radiation, that actually falls in the visible region of the spectrum. |
 | | Cherenkov radiation from a gamma ray is like a headlight beam streaming through the atmosphere -- by the time it reaches the ground, it has spread out to cover an area about 200 meters across. |
| chronicle.uchicago.edu /971023/stacee.shtml (1077 words) |
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