Focusing Telescopes in Nuclear Astrophysics

HESS (High Energy Stereoscopic System), a ground-based Cerenkov array telescopes has been operated since a few years and in 2004 has performed the ?rst Galactic plane scan with a sensitivity of a few percent of the Crab at energies above 100 GeV, resulting in the discoveryofeightsources,mostofwhichwithoutanycounterpartatdifferentenergies[1,2].