It is my very pleasant task to thank and congratulate the organisers of this Colloquium : the European Space Agency, through its Director General, Reimar Lüst, and Director of Science, Roger Bonnet, and the European University of Philosophy, through its Director, Jean-Pierre Faye. The linchpin in the preparations for this gathering, to whom we are greatly indebted, was Jean-Claude Pecker, assisted by Jean Schneider. Monique Orine and her team have shown admirable efficiency in coping with the practical difficulties of running this event. We owe thanks to NASA, represented by the astronaut J. Hoffman, courtesy of whom we have seen a display of quite remarkable images, and to the USSR Academy of Sciences, represented by Professor Ursool. Finally, the Ministère de la Recherche et des Enseignements Supérieurs has acted as host for our meetings and the Observatoire de Paris for our other business, and I speak for all of us in gratefully acknowledging their hospitality.