7 Summary

The heliosphere shields the solar system and all living creatures from galactic CRs. Since the Sun is a variable star it produces significant modulation of these charged particles in a variety of cycles. Cosmic rays are excellent indicators of the various solar cycle variations and studying them enlighten us about the characteristics of the Sun’s electrodynamic influence sphere. Such studies also inform us about the structural features and geometry of the heliosphere, including the solar wind termination shock, the heliosheath and the heliopause because they all influence the flux of CRs in the heliosphere, up to Earth.

Tremendous progress has been made since the beginning of the space age with the deployment of several space missions for detecting CRs over a wide range of energies, which stimulated theoretical and modeling research. Ten years ago, the size and geometry of the heliosphere and the importance of shock acceleration were all major unknown issues. Now that the Voyager spacecraft had crossed the TS and Voyager 1 is close to the heliopause, some of these entities and mechanisms are becoming reasonably known, at least, they cannot be considered ‘free’ parameters any longer.

The present understanding of the mechanisms of the global solar modulation of galactic CRs in the heliosphere is considered essentially correct, an amazing accomplishment for Parker’s theory that was developed in the early 1960s. The main obstacles and challenges are insufficient knowledge of the spatial, rigidity and especially the temporal dependence of the diffusion coefficients, covering the underlying features of solar wind and magnetic field’s turbulence.

Evidently, this field of research is alive-and-well with many aspects remaining a work in progress.

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