This volume of the Highlights of Astronomy contains the Invited Discourses and the proceedings or summaries of Joint Discussions, Special Sessions, and Working Group Meetings held at the XIInd IAU General Assembly in August 1994 in The Hague. While the three Invited Discourses are reproduced in the order of their appearance in the meeting programme, the Joint Discussions have been reordered according to their topics. Not included in this volume are the proceedings of the GA Symposia which will be published individually in the IAU Symposia series. I am most grateful to the authors of the invited discourses for preparing manuscripts in spite of heavy other commitments. It is a pleasure to express my appreciation of the work by Dr. Jacqueline Bergeron in organizing the XXIInd General Assembly, and I wish to thank all authors and meeting chairpersons for their cooperation and for providing their contributions in time to meet the customary publication schedule of this series. Special thanks are due to Ms. Monique Leger-Orine from the IAU office for considerable and patient assistance in the final editing, and to Dr. Tom Herbst from the Max­ Planck-Institute for Astronomy for permission to reproduce on the cover of this volume one of his IR images of Jupiter obtained just after the Comet Shoemaker-Levy 9 impact, one of the definite Highlights of Astronomy in 1994.

Preface; I. Appenzeller. I. Invited Discourses. Recent Advances in X-Ray Astronomy; Y. Tanaka. Earth Rotation Variation from Hours to Centuries; J. O. Dickey. The High Energy Frontier; C. Rubbia. II. Joint Discussions. Women in Astronomy; S. Torres-Peimbert. History of Astronomy; S. Débarbat. `75 Years of the IAU'. `Work in Progress'. Current Developments in Astronomy Education; J. R. Percy. Towards the Establishment of the Astronomical Standards; T. Fukushima. Nutation; V. Dehant. Timescales: State of the Art; E. Proverbio. Sun and Heliosphere - Challenges for Solar-Terrestrial Physics, Magneto- and Hydrodynamics; M. C. E. Huber. Helio- and Astroseismology; W. Däppen. Dust around Young Stars: How Related to Solar System Dust? Summary; M. S. Hanner. Accuracy of the HR Diagram and Related Parameters; M. Gerbaldi. Recent Advances in Convection Theory and Modelling: Summary; S. Sofia. Stellar and Interstellar Lithium and Primordial Nucleosynthesis; F. Spite. Extragalactic Planetary Nebulae; Y. Terzian. Activity in the Central Part of Galaxies; V. Trimble. Astrophysical Applications of Powerful New Atomic Databases; W. L. Wiese. `The New Atomic Databases'. `Stellar Atmospheres'. `Stellar Structure'. The Status of Archiving Astronomical Data: Summary; R.E.M. Griffin. III. Special Sessions. The Collision of Comet P/Shoemaker-Levy 9 with Jupiter; C. de Bergh. Gravitational Lens Monitoring: Summary; J.-P. Swings. IV. Working Group Meetings: A. H. Batten. Problems of Astronomy in Africa. International Catalog Projects. Index of Authors.