Excited cosmic plasmas

We describe some aspects of the energetic radiations of high-energy cosmical plasmas in stellar environments, mainly stellar chromospheres and coronae, and solar and stellar flare-type phenomena. As far as possible we discuss the morphology and physics of these plasmas, and we speculate on their origin. This paper is a review, partly of a historical character, describing particularly some contributions from the Astronomical Institute at Utrecht to this field of astrophysical research.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978.