Composition and Origin of Cosmic Rays

Particle astronomy - the study of cosmic radiation - was the first of the new astronomies to emerge in the twentieth cen- tury. Although cosmic-ray phenomena have been fruitfully investi- gated for some seventy years, the central engima - the origin of these high-energy particles - remains a challenge. Among the ob- servational clues to possible sites and mechanisms of cosmic-ray production, none carries more information than the composition and energy distribution of the particles arriving...