Gamma-Ray Astronomy

A brief description is given of the present status of gamma-ray astronomy, both galactic and extragalactic. More detailed attention is given to a specific question: the nature of the apparent 'gamma-ray sources'. The undoubted correlation of at least some of the sources with dense clouds of gas in the interstellar medium is discussed. A new analysis of the SAS II satellite data is described, and comparisons are made between the 'source catalogue' from these data with the well-known 2CG catalogue from the COS-B experiment. It is concluded that, although some of the 2CG sources are certainly pulsars and others are genuinely discrete, almost half of the unidentified sources are probably due to the cosmic ray irradiation of molecular clouds.