Astrophysics with the H.E.S.S. Cherenkov telescopes

The H.E.S.S. (High Energy Stereoscopic System) is an array of four imaging atmospheric Cherenkov telescopes designed to observe gamma rays above 100 GeV. The array has been in full operation since 2004 and has greatly increased the total number of known sources and source classes at these energies. The H.E.S.S. Collaboration is now extending the array with a fifth, very-large Cherenkov telescope which will reduce the energy threshold of the array and allow for the study of new source classes and phenomena as well as making deeper observations of currently known sources.