Our Extraordinary General Assembly is devoted to the memory of one of the greatest men of science to the genial Polish astronomer - Nicolaus Copernicus. The main service of Copernicus which has made his name immortal was in finding the correct interpretation of the planetary motions we observe. Instead of geocentric notions, which proved unable to explain the accumulated bulk of empirical data on the apparent motions of planets he has put forward and advocated the notion of a solar system thus presenting the true picture of the part of the Universe we live in. The scientific revolution started by him was continued by Galileo and Kepler and was crowned with the great theoretical generalizations of Newton. As a result a foundation has been created for the most exact theories of motions in the solar system which were developed during the next centuries. These theories in their modern form give also the possibility to solve all the problems concerning the orbital motions of spaceships.

At this stage we can not yet boast that in the study of nuclei of galaxies and their activity we have reached the level which existed in planetary astronomy even before the works of Newton. Only 15 years elapsed from the moment when the idea of activity of nuclei of galaxies was clearly formulated (Ambartsumian, 1958). During these years discoveries of the greatest importance have been made. New unexpected discoveries occur almost each year. These discoveries influence decisively our notions on the diversity of objects and phenomena in the distant space, but they are still insufficient for the construction of adequate theories. In order to penetrate into the very nature of nuclear phenomena we require new observations, new measurements and new data. And if some optimists imagine that the time has already ripen to build a general theory of these phenomena, the more cautious astronomers would like to consider a more or less satisfactory systematization of observational data concerning the activity of nuclei and the understanding of external physical processes accompanying it as a tremendous success.