This second volume of Reviews in Modern Astronomy continues the new series of publications of the Astronomische Gesellschaft (AG). In order to bring the scientific events of the meetings of the society to the attention of the worldwide astronomical community, it was decided to devote a new annual publication, Reviews in Modern Astronomy, exclusively to the invited reviews, the Karl Schwarzschild lectures, and the highlight contributions from leading scientists reporting on recent progress and scientific achievements at their institutes. Volume 2 comprises the contributions presented during the spring meet­ ing of the AG at Friedrichshafen in April 1989, which was dedicated to the topic "Astrophysics with Modern Technology - Space-based and Ground-based Systems", as well as those delivered at the fall meeting at Graz, Austria in September 1989. The Karl Schwarzschild lectures constitute a special series by outstanding scientists honoured with the Karl Schwarzschild medal of the Astronomische Gesellschaft. Between 1959 and 1987 the following scientists presented Karl Schwarzschild lectures at meetings of the Astronomische Gesellschaft: Martin Schwarzschild (1959) George Field (1978) Charles Fehrenbach (1963) Ludwig Biermann (1980) Maarten Schmidt (1968) Bohdan Paczynski (1981) Bengt Stromgren (1969) Jean Delhaye (1982) Antony Hewish (1971) Donald Lynden-Bell (1983) Jan H. Oort (1972) Daniel M. Popper (1984) Corne lis de Jager (1974) Subrahmanyan Chandrasekhar (1986) Lyman Spitzer Jr.