Planetary nebulae are the classic subject of astrophysics. The physical pro cesses occurring in this highly ionized gaseous medium, the formation of emis sion lines in clearly specified conditions, the continuous emission extending from the far ultraviolet up to infrared and radio frequencies, the generation of exotic forms of radiation predicted by atomic physics, along with methods for deciphering the observed spectra and detecting physical and kinematic parameters of the radiating medium, etc. - all these problems form the solid foundations of the physical theory of gaseous nebulae. They are an essential part of the arsenal of powerful tools and concepts without which one cannot imagine understanding and interpreting the enormous diversity of processes taking place in the Universe - in gaseous envelopes surrounding the stars of various classes, from cool dwarfs and flare stars up to hot supergiants, as well as in stellar chromospheres and coronae, in atmospheres of unstable and anomalous stars, in circumstellar clouds and gaseous shells born in nova and supernova explosions, in diffuse nebulae and the interstellar medium, in interacting binary systems, in galaxies with emission lines, in quasars, etc. The last thirty years have seen a turning-point in our knowledge concern ing the very nature of planetary nebulae (PNs). The radio emission of PNs was discovered after it was predicted theoretically. On the other hand, the powerful infrared emission discovered both in the continuum and in emission lines was never expected.

Planetary nebulae are the classic subject of astrophysics. The physical pro cesses occurring in this highly ionized gaseous medium, the formation of emis sion lines in clearly specified conditions, the continuous emission extending from the far ultraviolet up to infrared and radio frequencies, the generation of exotic forms of radiation predicted by atomic physics, along with methods for deciphering the observed spectra and detecting physical and kinematic parameters of the radiating medium, etc. - all these problems form the solid foundations of the physical theory of gaseous nebulae. They are an essential part of the arsenal of powerful tools and concepts without which one cannot imagine understanding and interpreting the enormous diversity of processes taking place in the Universe - in gaseous envelopes surrounding the stars of various classes, from cool dwarfs and flare stars up to hot supergiants, as well as in stellar chromospheres and coronae, in atmospheres of unstable and anomalous stars, in circumstellar clouds and gaseous shells born in nova and supernova explosions, in diffuse nebulae and the interstellar medium, in interacting binary systems, in galaxies with emission lines, in quasars, etc. The last thirty years have seen a turning-point in our knowledge concern ing the very nature of planetary nebulae (PNs). The radio emission of PNs was discovered after it was predicted theoretically. On the other hand, the powerful infrared emission discovered both in the continuum and in emission lines was never expected.

This authoritative volume provides a comprehensive review of the origin and evolution of planetary nebulae. It covers all the stages of their evolution, carefully synthesizes observations from across the spectrum, and clearly explains all the key physical processes at work. Particular emphasis is placed on observations from space, using the Hubble Space Telescope, the Infrared Space Observatory, and the ROSAT satellite. This book presents a thoroughly modern understanding of planetary nebulae, integrating developments in stellar physics with the dynamics of nebular evolution. It also describes exciting possibilities such as the use of planetary nebulae in determining the cosmic distance scale, the distribution of dark matter and the chemical evolution of galaxies. This book provides graduate students with an accessible introduction to planetary nebulae, and researchers with an authoritative reference. It can also be used as an advanced text on the physics of the interstellar medium.

This written account of the Symposium on Planetary Nebulae was prepared from manuscripts submitted by the participants. Nearly every paper that was presented at the meeting is reproduced here, in either complete or abbreviated form. The dis cussions have been somewhat shortened and rearranged, but we have tried to preserve the essential points and the general tenor of the exchanges. Participants who spoke in the discussion were asked immediately for written remarks, which were then edited, reproduced, and circulated at the meeting by the highly effective local Secretariat organized by Dr Perek. In addition, notes of the discussion taken by Mrs Edith F. Swan and by the undersigned were used. We wish to thank all the authors for their unusually good cooperation. We are especially grateful to Dr Minkowski, who kindly provided many excellent repro ductions of Mount Wilson and Palomar photographs, mostly taken by himself, of various planetary nebulae. We are particularly indebted to Mrs Swan, who attended the Symposium, made notes on the papers and discussions as they occurred, and did much of the checking and editing of the manuscripts. In addition, we are very grateful to Mrs Evelyn Seaver, who also did much of the checking, editing, and retyping of manuscripts, and to Dr B.L. Webster, Miss Rebecca Todd, Mr Joseph Tapscott, and Mr Dennis Schatz, who provided excellent assistance in the preparation of this volume.

The publication in English of this monograph seems to me to indicate the ever increasing interest of astrophysicists in the physical and dynamical problems of planetary nebulae-one of the most interesting and fruitful branches of theoretical astrophysics. Their interest in part arises from the fact that the methods of identify ing the physical processes occurring in planetary nebulae, as well as the many theo retical results, are now acquiring a degree of uni versality as their sphere of application increases. Finally, the special cosmic significance of planetary nebulae is becoming apparent. The English edition of Planetary Nebulae differs considerably from the Russian version published in 1962, primarily because of the new results included in it, but also because of numerous editorial revisions. The problems of magnetic fields and hydrodynamics in planetary nebulae are beginning to occupy an important place in the study of the dynamics of these objects. Recent studies by D. H. Menzel confirm the idea advanced in the present mono graph as to the existence of magnetic fields in planetary nebulae. New light is being cast on the dynamics of planetary nebulae by the hydrodynamic investigations of F. D. Kahn, W. G. Mathews and others. Unfortunately I was not able to include these and other interesting results in the present edition.

Thoroughly revised and expanded throughout, the new edition is a graduate-level text and reference book on gaseous nebulae, nova and supernova remnants. Much of the new data and new images are from the Hubble Space Telescope with two wholly new chapters being added along with other new features. The previous edition which was tried and tested for thirty years has now been succeeded by a revised, updated, larger edition, which will be valuable to anyone seriously interested in astrophysics.