E. Leer

TL;DR: The problem of the origin of galactic cosmic rays is a particularly difficult one despite the fact that rather detailed measurements of the properties of cosmic rays can be made, at least in the vicinity of the Sun as discussed by the authors, and the current situation has been well reviewed by Lingenfelter who points out that there are several linked problems to be solved, namely the question of sources and acceleration mechanisms, propagation within the galaxy, escape from the galaxy and of course solar modulation which affects the interpretation of the observations, especially below ~ 1 GeV/nuc.