It was about fourteen years ago that some of us became intrigued with the idea of searching the sky for X-ray and gamma-ray sources other than the Sun, the only celestial emitter of high-energy photons known at that time. It was, of course, clear that an effort in this direction would not have been successful unless there occurred, somewhere in space, processes capable of producing high-energy photons much more efficiently than the processes responsible for the radiative emission of the Sun or of ordinary stars. The possible existence of such processes became the subject of much study and...

Riccardo Giacconi Harvard/Smithsonian Center for Astrophysics The meeting of the High Energy Astrophysics Division of the American Astronomical Society, held in Cambridge, Massachusetts on January 28- 30, 1980, marks the coming of age of X-ray astronomy. In the 18 years since the discovery of the first extrasolar X-ray source, Sco X-l, the field has experienced an extremely rapid instrumentation development culminating with the launch on November 13, 1978 of the Einstein Ob servatory (HEAO-2) which first introduced the use of high resolution imaging telescopes to the study of galactic and...

The IAU Symposium No. 55 on 'X-Ray and Gamma-Ray Astronomy' has occurred, not entirely by coincidence, at an important moment in the development of these new branches of observational astronomy. In X-ray astronomy the data from the first X-ray observatory UHURU have contributed to a new view of the X-ray sky and a new conception of the nature and properties of galactic and extragalactic X-ray sources. In gamma-ray astronomy the exciting and often controversial nature of the results underlines the importance of the forthcoming launch of SAS-B, the first orbiting y-ray observatory. As Bruno...

It was about fourteen years ago that some of us became intrigued with the idea of searching the sky for X-ray and gamma-ray sources other than the Sun, the only celestial emitter of high-energy photons known at that time. It was, of course, clear that an effort in this direction would not have been successful unless there occurred, somewhere in space, processes capable of producing high-energy photons much more efficiently than the processes responsible for the radiative emission of the Sun or of ordinary stars. The possible existence of such processes became the subject of much study and...

Riccardo Giacconi Harvard/Smithsonian Center for Astrophysics The meeting of the High Energy Astrophysics Division of the American Astronomical Society, held in Cambridge, Massachusetts on January 28- 30, 1980, marks the coming of age of X-ray astronomy. In the 18 years since the discovery of the first extrasolar X-ray source, Sco X-l, the field has experienced an extremely rapid instrumentation development culminating with the launch on November 13, 1978 of the Einstein Ob servatory (HEAO-2) which first introduced the use of high resolution imaging telescopes to the study of galactic and...