This book is a translation, by Mr. S. Dunlop, FRAS, of the second German edition of Veranderliche Sterne published by Johann Ambrosius Barth Ver- lag, Leipzig, DDR, and Springer-Verlag, Berlin Heidelberg New York Tokyo. We have used the opportunity to make improvements and changes in a few places and to add details of new results and discoveries. The foreword to the second German edition remains no less valid for this one, including the changes. We would like to express our thanks to Mr. Dunlop for his expert and sympathetic translation and for the many improvements he suggested. December 1984 G. RICHTER and W. WENZEL Preface to the Second German Edition The suggestion that a second edition of this book should be prepared came equally from the readers, the publishers, and from the editors of the first edition. By a lucky coincidence the completion of the manuscript and the composition of these lines comes at the time of the 90th anniversary of the birth of Cuno Hoffmeister, the author of the first edition, and consequently this current work may be dedicated to his memory.

Table of Contents:
1. General Introduction.- 1.1 Introduction and General Summary.- 1.2 Explanation of Some Fundamental Concepts.- 1.3 Light-Curves and Periods.- 1.4 Julian Date and the Expression of Dates and Times.- 1.5 Nomenclature of Variable Stars.- 2. Pulsating Variables.- 2.1 Classical Pulsating Stars.- 2.1.1 Historical Summary and Classification.- 2.1.2 ? Cephei and W Virginis Stars.- 2.1.3 RR Lyrae Stars.- 2.1.4 ? Scuti Stars.- 2.2 Slowly-Varying, Pulsating Stars.- 2.2.1 Mira Stars.- 2.2.2 Semiregular, Irregular and RV Tauri Stars.- 2.3 Non-Radial Pulsators.- 2.3.1 ? Cephei Stars.- 2.3.2 ZZ Ceti Stars.- 3. Eruptive Variables.- 3.1 Eruptive Binaries.- 3.1.1 Cataclysmic Variables - a Summary.- 3.1.2 Novae.- 3.1.3 U Geminorum Stars.- 3.1.4 AM Herculis Stars or Polars.- 3.1.5 Properties and Models of Cataclysmic Variables.- 3.1.6 Symbiotic Stars.- 3.1.7 X-Ray Binaries.- 3.2 Supernovae.- 3.3 Stars at an Extremely Early Stage of Evolution.- 3.3.1 Historical.- 3.3.2 T Tauri Stars and Related Objects.- 3.3.3 Flare Stars.- 3.4 Hot Variables with Extended Shells.- 3.4.1 S Doradus-Type Variable Supergiants.- 3.4.2 ? Cassiopeiae Stars.- 3.4.3 Variability in Planetary Nebulae or Their Central Stars.- 3.5 R Coronae Borealis Stars.- 3.6 ?-Ray Bursters.- 3.7 Other Types of Object.- 3.7.1 BY Draconis Stars and Similar Objects.- 3.7.2 Pulsars.- 3.7.3 ?2 Canum Venaticorum (Magnetic) Stars.- 4. Eclipsing Stars.- 4.1 General.- 4.2 Geometrical Properties.- 4.3 Classification.- 4.4 Analysis of the Light-Curve.- 4.5 Period Changes.- 4.5.1 Periodic Changes.- 4.5.2 Non-Periodic Changes.- 4.6 Statistics.- 4.7 Some Interesting Eclipsing Systems.- 4.8 Concluding Remarks on the Evolution of Close Binary Systems.- 5. Supplement to the Classification.- 5.1 Variables in Clusters.- 5.1.1 Open Clusters.- 5.1.2 Globular Clusters.- 5.2 Variables in Extragalactic Systems.- 5.2.1 Magellanic Clouds.- 5.2.2 Other Extragalactic Systems.- 5.3 Active Galaxies.- 5.3.1 General.- 5.3.2 Seyfert Galaxies.- 5.3.3 Quasars.- 5.3.4 BL Lacertae Objects.- 6. The Discovery of Variable Stars.- 6.1 Basic Considerations.- 6.2 Methods and Instruments.- 6.3 The Theory of Discovery Probability.- 6.4 Determination of Discovery Probability from Given Light-Curves.- 6.5 Comparison of Theoretical and Empirical Discovery Probabilities - The Influence of Observer and Method.- 6.6 Discovery Statistics.- 6.7 Preliminary Designations of Variable Stars.- 7. The Significance of Variable Stars for Research on the Structure of the Galaxy and Stellar Evolution.- 7.1 Methods.- 7.2 Results.- 7.3 The Galactic Halo.- 7.4 Remarks on the Evolution of the Galaxy.- 8. Observational Methods and Organizations.- 8.1 Observations.- 8.1.1 Photometric Observations.- 8.1.2 Spectrographic and Other Observations.- 8.1.3 Bright Variables.- 8.1.4 Amateur Collaboration.- 8.2 Organization.- 9. Literature.- 9.1 Brief Notes About Stellar Catalogues and Atlases.- 9.2 General Summaries, Compilations and Review Articles.- 9.3 References.- Star Index.