Highlights of Astronomy : As Presented at the XIIIth General Assembly of the I.A.U. 1967

The XIIlth General Assembly of the International Astronomical Union, held in Prague from 22 to 31 August, 1967, brought together more than 1800 active astron­ omers from 40 countries. The agenda of the Assembly ranged from administrative questions to highly intricate scientific problems. Thirty-eight Presidents of the IAU Commissions contributed by their reports to a detailed survey of Astronomy for the period 1964-67. These reports were published in the Transactions of the IAU, Volume XIIIA. Transactions volume XIIIB bring the results of the administrative meetings and of the meetings of Commissions held during the General Assembly. The present volume is devoted to the most important scientific results of the General Assembly as presented in the Invited Discourses, Joint Discussions, and at Special Meetings. It is an established policy of the Union to invite prominent astronomers to hold, during the General Assembly, formal discourses on topics of major importance due to recent significant developments. These Invited Discourses cover, as a rule, broad fields of astronomical interest and are meant to give basic information also to scien­ tists from other branches. Subjects which call for a more detailed technical approach are dealt with in the Joint Discussions or at Special Meetings. Here, invited speakers present authoritative surveys complemented by communications on current or envisaged projects. The proceedings of two other meetings, on Moon Probes and on Coordination of Solar Observations Made at Ground-based Observatories and with Space Vehicles, are of a sufficiently wide interest to warrant the inclusion into this volume.

Invited Discourses.- A. Exploring the Moon.- B. Couches extérieures et structure interne des étoiles.- C. Radio Galaxies and Quasars, I.- D. Radio Galaxies and Quasars, II.- Joint Discussions.- A. New Techniques in Space Astronomy.- Recent Techniques in Solar Optical Astronomy from Space.- Ultraviolet Astronomy.- New Techniques in X-Ray Astronomy.- Solar and Interplanetary Magnetic Fields and Plasmas.- Infrared Astronomy.- Some Problems and Instrumental Features of Sub-millimeter Astronomy.- New Techniques in Space Radio-astronomy.- B. X-Ray Astronomy.- Surveys of X-Ray Sources.- Recent Results on Extragalactic Cosmic X-Ray Sources from Rocket and Balloon Flights.- A Cosmic X-Ray Survey in the Southern Hemisphere.- Results from Detailed Studies of X-Ray Sources.- The X-Ray Spectra of Cygnus XR-1 and the Crab Nebula.- Optical and Radio Information.- Theoretical Review.- X-Rays Radiation of a Neutron Star as a Result of Gas Accretion.- The Cosmic X-Ray Background.- C. The Lithium Problem.- The Occurrence of Lithium in Stars.- Evidence for Lithium Destruction and Synthesis in Main-Sequence and Subgiant Stars of about Solar Mass.- Observations of Beryllium in Stars.- Lithium Observations in the Sun.- On the Lithium Abundance in Sunspots and the Undisturbed Solar Atmosphere.- The Formation of Li, Be, B Isotopes by the Spallation of CNO.- What can we learn from Li and Be Stellar Observations?.- The Mixing of Lithium.- D. Modem Problems of Fundamental A strömetry.- The AGK3, SRS and Related Projects.- Recent Work on Fundamental Astrometry in the U.S.S.R.- Meridian Observations at Santiago, Chile.- Preliminary Results of the Determination of Absolute Proper Motions of Stars referred to Galaxies.- Desiderata for FK5.- Precession and Galactic Rotation on the Basis of Various Proper Motion Systems.- The Relationships between Various Techniques for obtaining Proper Motions.- The Place of Accurate Proper Motions in Galactic Research.- Études sur l’emploi de Recouvrements de Plaques pour l’établissement de Catalogues Photographiques.- The Overlap Approach toward the Derivation of Photographic Stellar Coordinates.- Report on Overlap Methods in Photographic Astrometry.- Relative Star Positions from Overlapping Photographic Plates.- E. Extragalactic Radio Sources.- Optical Studies of Extragalactic Radio Sources.- Burbidge Optical Spectra of Extragalactic Radio Sources.- Radio Observations of Angular Structure.- Radio-Source Spectra and their Time Variations.- Infrared Observations of QSS.- Millimetre-Wave Observations.- The Nature of the Red-Shifts in Quasi-Stellar Objects.- Theories proposed to explain Quasi-Stellar Objects and Radio Galaxies.- A Cosmological Interpretation of the Absorption-Line Spectra of QSO.- The Evolution of Quasi-Stellar Sources and Radio Galaxies.- The Magnetodynamic Model of Quasars.- A Rotating Disk Model for a Quasar.- Shorter Contributions.- F. Close Binaries and Stellar Evolution.- Opening Remarks.- On the Origin of the Algol Systems.- The Evolution of Close Binaries and the Formation of the Wolf-Rayet Stars.- White Dwarfs in Close Binary Systems.- Arguments indicating that Ap and Am Stars are Evolved Spectroscopic Binaries.- Investigation of Possible Abundance Anomalies in Close Binaries of Spectral Types A0-A2 & F5–F6.- The Evolution of Close Binaries and the Am Stars.- Origin of Binaries from a Consideration of Angular Momentum.- The Origin and Early Evolution of Close Binary Stars.- The Structure of W Ursae Majoris Systems.- Comments.- A Model for the Nova Outburst.- Concluding Remarks.- Special Meetings.- A. Lunar Probes.- A Description of the Lunar Orbiter Spacecraft.- Photographic Results of the Lunar Orbiter Program.- B. Coordination of Solar Observations made at Ground-Based Observatories and with Space Vehicles.- The Need of Ground-Correlated High-Resolution Space Observations in the Visible.- Space Observations Needed for Improving Our Knowledge of Solar Flares.- Space Observations of Flare Sprays and Related Surge Phenomena.- The Needs and Requirements from the Standpoint of the Ultraviolet Solar Observations.- Hard Solar X-ray Bursts.- Solar Gamma Rays and their Correlation with Space and Ground-Based Observations.- The Coordination of Ground-Based and Space Observations: Summary.