The origin of cosmic rays

Cosmic radiation was discovered by Viktor Hess in 1912. Subsequent research and discoveries about cosmic radiation are set in a chronological context to show how current understanding of this phenomenon has been built up. The questions what are cosmic rays, what do they do and where do they come from are addressed with clues from gamma ray experiments used to find the answers. Cosmic rays, Coviant Molecular Clouds and cosmology are also considered. (author)