PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY
HESS gamma ray telescope mirror tests. Technician examining a mirror that will be used in the HESS (High Energy Stereoscopic System) array in Namibia. The telescopes in this array are Imaging Atmospheric Cherenkov Telescopes (IACTs), and they detect the flashes of Cherenkov radiation produced as high-energy gamma rays and cosmic rays hit the Earth's atmosphere. The HESS array is used to investigate gamma ray sources such as supernova remnants and pulsars. The four telescopes in the array use hundreds of mirrors like this one, each 60 centimetres in diameter and made of aluminised glass with a silica coating. The mirror must meet a high reflectivity standard. The HESS array has been operational since December 2003. Photographed in January 2006.
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