The Gamma-Ray Sky

Abstract

When we talk of Gamma-Ray Astronomy we refer in general to celestial photons covering the energy domain from a fraction of MeV up to the highest detected energies at hundreds or thousands of GeV. The six to seven decades altogether spanning the overall energy range constitute a very wide domain to be compared with those of the optical (less than one decade) or of the neighbouring X-Ray Astronomy (about two decades). The observational technique varies widely with changing energy; detector performances and characteristic parameters are not, in general, comparable.