This book was written for readers interested in learning about the disciplines, methods and results of space research, perhaps because they happened upon the field during the course of their higher education or professional career, or perhaps because they simply feel an urge to know more about the space environment of the Earth. The present monograph is based on lectures cover ing the same topic, which have been held regularly over the past years at the University of Bonn. Like the lecture series, the book is directed at a relatively broad group of students and interested laypersons, the only...