Publisher's Synopsis
IAU Symposium No. 121 was hosted by the Byurakan Astrophysical Observatory in Soviet Armenia, almost 30 years after Ambartsumian's pioneering ideas about galaxy activity were first published and almost exactly 20 years after the first Byurakan IAU symposium on nuclear activity (No. 29, "Non-stable Phenomena in Galaxies, May 1966). Although the proceedings of the first Byurakan symposium were not published in English, that conference provided a definitive impulse to the field, as Ambartsumian's ideas had done 10 years earlier. The Byurakan Astrophysical Observatory was thus a particularly appropriate setting for IAU 121. The symposium was also very timely since many new exciting results were presented which will surely revolutionize many of our present ideas about nuclear activity in galaxies and QSO's. The first results of the by now famous Markarian survey were presented by B.E. Markarian in the first Byurakan conference. Unfortunately, his untimely death prevented him from attending the second conference, but the influence of his fundamental work was certainly felt.
