H.E.S.S. (High Energy Stereoscopic System) is a system of imaging atmospheric Cherenkov telescopes, located in Namibia, for the investigation of cosmic gamma-rays in the energy range between 100 GeV and several TeV. The first of the four telescopes of the Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003, and were officially inaugurated on September 28, 2004.
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