From 17 to 21 April 1967 a Study Week was held in the hotel 'De Bilderberg' near Arnhem, Holland, with the purpose to establish a new, and if possible, generally acceptable working model for the quiet parts of the solar photosphere and low chromosphere. The organizers of the conference hoped that even if this latter goal appeared too far to be reached, such a meeting would still be useful, if only for enumerating the crucial problems in solar photospheric research, and for defining future subjects of research. About twenty solar physicists from outside the Netherlands participated in the...

The primary inducement for organizing an international Conference on 'Image Processing Techniques in_Astronomy' was the fact that the recording microdensitometer VAMP ('Vol Automatische Micro Photometer') of the Utrecht Astronomical Institute was operative for a few years. The necessity of comparing the in- strument and its performance with similar instruments nowadays available at many other institutes, was stimulating enough to organize a meeting on the above subject. It took place in Utrecht on March 25, 26 and 27, 1975. The Scientific Organizing Committee consisted of J. Borgman...

This volume contains the fifteenth tri-annual reports of the Presidents of the forty Commissions of the International Astronomical Union; it refers to the progress in our discipline during the three years 1970, 1971 and 1972. As compared to earlier volumes a gradual change in character is unmistakable. The ever increasing flow of publications, combined with the obvious necessity to keep the Reports at a reasonable size and price level has gradually forced the Commission Presidents to be more selective than before in drafting their Reports. I have certainly stimulated them into that direction...

No part of the Hertzsprung-Russell diagram shows a more pronounced diversity of stellar types than the upper part, which contains the most luminous stars. Can one visualize a larger difference than between a luminous, young and extremely hot Of star, and a cool, evolved pulsating giant of the Mira type, or an S-type supergiant, or - again at the other side of the diagram - the compact nucleus of a planetary nebula? But there is order and unity in this apparent disorder! Virtually all types of bright stars are evolutionally related, in one way or the other. Evolution links bright stars. In...