Sounding Solar and Stellar Interiors: General Introduction

in the many senses of the word. It is a tremendous amount of fun with a really large number of interesting problems, vigorous dialectic between observations and theory, rapid progress, fantastic observational opportunities, and extraordinarily stimulating colleagues. It is grand, in its phenomenally rapid development, the challenges that it presents, and the importance of the problems that it addresses, as well as its promise for the future. It is doing very, very well as seen in the vitality of the community of researchers pursuing it, in the major investments made in acquiring beautiful new data to fuel its continuing progress, and in the many new problems that open before us as the current ones achieve a measure of \understanding". This Symposium marks a signiicant milestone in the development of helioseismology { the beginning of observations from GONG and SoHO { and it may be diicult to recall that, in many senses, the discipline began but a scant twenty years ago, here in Nice at a conference entitled \Physique des Mouvements dans les Atmosph eres Stellaires" at which Franz-Ludwig Deubner rst presented his remarkable observational demonstration that the \\ve-minute oscillations" were indeed normal modes of oscillation of the solar interior Figure 1 ]. Contrast that landmark observation with the state of the art today Figure 2 ] to see how dramatic has been our progress. This meeting also marks the passing of time and the loss of two of the truly great personalities of the eld of the \physique des mouvements dans les atmosph eres stellaires" who participated very actively in that meeting: Philippe Delache and Dick Thomas. They were truly great gures in their contribution of new ways of thinking about the Universe, in their eeorts