Introduction

Abstract

Plasma regions are main sources of extra-terrestrial radiation. It sounds quite natural, since matter in the Universe (for example, stars and their atmospheres, interstellar and interplanetary medium, planet ionospheres and magnetospheres) is mostly in a plasma state. The rare exceptions among radiation sources, such as planet surfaces and lower atmospheres, are not considered in this book. In this respect, the diversity in profiles and scales of phenomena in astrophysical plasmas is not at all surprising. Among the others, basic effects come from electromagnetic processes which govern plasma dynamics, motion and acceleration of charged particles, generation and transfer of radiation. This book focuses on the problems related to generation and propagation of radiation in, as well as its influence on plasma. Thus, section 1.1, the first one of this introductory chapter, points out those plasma characteristics which finally determine the conditions for generation and propagation of electromagnetic radiation; the next section 1.2 reviews the main characteristics of radiation; in the last one, section 1.3, the properties of astrophysical radiation sources which originate due to their spatial motion are discussed and basic definitions necessary to establish general classification of radiation mechanisms are introduced.