The year 1973 marked the highest peak of IAU activity up to now. Besides the Gen eral Assembly in Sydney, and the Extraordinary General Assembly in Poland, there were held eleven IAU Symposia and one Colloquium. Several IAU Publications cover this activity. The Proceedings of the Symposia are published in separate Volumes, while the Transactions of the General Assembly and of the Extraordinary General Assembly contain short reports of the Commission meetings, the administrative sessions, and the opening ceremonies. The present Volume covers some of the scientific Highlights of the General As sembly and of the Extraordinary General Assembly. It contains five Invited Dis courses given in Sydney and Poland, some selected papers, and the Joint Discussions at the General Assembly of Sydney. Of course, there were many more papers of special interest presented in Sydney that could not be included in this Volume. Their titles can be seen in the reports of the various Commissions. It is regrettable that the Invited Discourses of C. H. Townes (Interstellar Molecules) and F. J. Low (Infrared Astronomy) were not submitted for publication. Also only five papers or abstracts of the Joint Discussion on the 'Origins of the Moon and Satellites' have been available. Despite these minor shortcomings, I believe that the present Volume is faithful to its title: it gives a substantial part of the Highlights of Astronomy in 1973.

Inhalt
Invited Discourses.- A New Look at the Sun.- Early Stages of the Universe.- The Physics of the Interstellar Matter.- Galaxies and Their Nuclei.- The Astronomy and Cosmology of Copernicus.- Selected Papers.- X-Ray Sources in Close Binary Systems.- The Next Decade in Stellar Atmospheres Theory.- The Future of Observational Stellar Atmospheres.- The Next Decade of Theoretical Solar Physics.- The Next Decade in Observational Solar Research.- Asymmetry in Solar Spectral Lines.- Joint Discussions.- I. Precession, Planetary Ephemerides and Time Scales.- Introductory Remarks.- Pro and Contra Changes in the Conventional Values of Precession.- The Calculation of the Nutations.- Planetary Ephemerides.- Astronomical Units, Constants and Time-Scales.- II. Stellar Infrared Spectroscopy.- High Resolution Interferometry of Cool Stars.- Presentation and Interpretation of High Resolution In frared Spectra of Late-Type Stars.- High Resolution Spectra of M and C Stars by Fourier Trans form Spectroscopy.- Scans and Narrow-Band Photometry of Late-Type Stars in the One-Micron Region.- Medium Resolution Stellar Spectra in the Two-Micron Region.- Fourier Transform Spectrophotometry and its Application to the Study of K-Giants.- Interpretation of Carbon Stars Spectrafrom Model Atmospheres Computations.- Stellar Spectroscopy at 1.1 ?.- Open Discussion.- III. Kinematics and Ages of Stars Near the Sun.- Preface.- The Ages of Stars in the Neighbourhood of the Sun.- Gould's Belt.- Red Variables and Their Main Sequence Progenitors.- Low Luminosity Stars and White Dwarfs.- The Kinematics and Ages of Stars in Gliese's Catalogue.- The Third and Fourth Moments of the Local Stellar Velocity Distribution.- The Abundance and Age Distribution of 500 F Stars in the Solar Neighbourhood.- The Space Density of Faint M-Dwarfs.- The Correlation Between Kinematical Properties and Ages of Stellar Populations.- Space Distribution and Motion of the Local H i Gas.- Influence of a Spiral Gravitational Field on the Observational Determination of Galactic Structure.- Solar Neighbourhood as the Local Macroscopic Volume Element Within the Galaxy.- How Can It All Be Stable?.- Closing Remarks.- IV. Origins of the Moon and Satellites.- On the Growth of the Earth-Moon System.- Evidence for Lunar-Type Objects in the Early Solar System.- The Movement of Small Particulate Matter in the Early Solar System and the Formation of Satellites.- Gravitational Collapse and the Formation of the Solar Nebula.- The Principle of Least Interaction Action.- V. Jovian Radio Bursts and Pulsars.- Summary.- VI. The Outer Layers of Novae and Supernovae.- The Chemical Composition of the Envelopes of Novae.- The Shell of V603 Aql and the Early Stages of the Nova Event.- Spectrophotometry of Supernovae.- On the Physical Model of Supernovae Close to Light Maximum.- Supernova Remnants.- Soft X-Ray Observations of Supernova Remnants.- Report on the Lecce Conference on Supernovae.