Bücher der Reihe Geophysics and Astrophysics Monographs

Only a few positive experimental results have been reported, in spite of an expenditure of considerable effort by many people: in particular, the possible Galactic Center emission line (473 to 530keV) and 'Y-ray lines at several energies (e.

Stellar physics itself is benefiting greatly from solar discoveries, but, in tum, our understanding of many solar phenomena (such as sunspots, sunspot cycles, the corona and the solar wind) will undoubtedly increase in the future due to their observation under different conditions in other stars.

Double and multiple stars are the rule in the stellar population, and single stars the minority, as the abundance of binary systems in the space surrounding the sun shows beyond doubt.

This book is an outgrowth of the notes made for the semester lectures on 'Problems of Extragalactic Astronomy' given almost annually during two decades at the Ob­ servatorio Astronomico of the Universidad de Cordoba. Shorter versions were also given at La Plata, Santiago de Chile, Sao Paulo, Rio de Janeiro and Paraiba. E. Scalise made a Portuguese language version of the notes and encouraged me to publish them; although my friend J. Kleczek is to be blamed for the idea of this book. Not every subject on Extragalactic Astronomy has been touched in this book: instead I have followed those which interested me during 25 years of professional practice in this part of the world. I acknowledge helpful suggestions from M. Pastoriza and G. Carranza, the com­ prehension of Director L. Milone, and the collaboration of the staff of the Observa­ tory in Cordoba. R. Tschamler's humor and wit made light the task of producing the English version and M. Pizarro's devotedness produced the edited MS. To both of them I am in deep gratitude. "A book is published out of necessity, otherwise the author would spend his entire life polishing the originals" was the answer given by J. L. Borges to an inquisi­ tive journalist. These words explain why this book is so different from the lecture notes, and also from the book I was hoping for. I thank B. McCormac and the D. Reidel Publ. Co. for my salvation from Borges' inferno.

This volume, together with its two companion volumes, originated in a study commis sioned by the United States National Academy of Sciences on behalf of the National Aeronautics and Space Administration. This volume is devoted to 'The Solar Interior', except that the volume begins with one chapter reviewing the contents of all three volumes.