The IAU Symposium 109, sponsored by IAU Commission 2( and co-sponsored by Commissions 8 and (0, was originally scheduled to be held in Merida, Venezuela, but eventually took place at the University of Florida in Gainesville from January 9 to January 12, 1984. The Scientific Organizing Committee consisting of Peter Brosche (FRG), John Davis (Australia), Jean Delhaye (France), Erik H9Sg (Denmark), James A. Hughes (USA), C. Andrew Murray (UK), Dimitri D. Polozhentsev (USSR), Jurgen Stock (Venezuela), Catherine Turon (France), Arthur R. Upgren (USA), Gart Westerhout (USA), Arno Witzel (Germany, FR), and Shu- Hua Ye (PRC), was chaired by Heinrich Eichhorn (USA). The Local Organizing Committe (chaired by Robert J. Leacock) included, in addition, Jeanne Kerrick, Carl Cole, Billy Cooke, Lance Erickson, Mary Jane Taylor, Wan-xian Wang and James Webb. The following chaired sessons during the Symposium: Shinko Aoki (Japan), Wilhelm Gliese (Germany, FR), Bernard Guinot (France), Kenneth Johnston (USA), Jean Kovalevsky (France), Kaj Aa. Strand (USA), George Teleki (Yugoslavia), and William van Altena (USA). All papers included in this volume were refereed. A significant part of them were not appropriate for publication as originally submitted, mostly for reasons of language. Some were therefore heavily edited. The papers originally submitted in Russian were translated into English by Eva Eichhorn. Many of the papers were retyped at the Department of Astronomy of the University of Florida.