The Swiss Society for Astrophysics and Astronomy organizes each year in
the late winter or early spring an advanced course. The format of the
school is always iden- tical: three leading lecturers are invited to
cover the subject in nine or ten lectures each and to deliver a written
version of their lecture notes. Lectures are held in the morning and
late afternoon, thus leaving ample time for discussion and skiing. These
arrangements prove very convivial and lead to an excellent atmosphere in
which to learn exciting new subjects and establish contacts with
colleagues. A wide variety of people attend the school, including many
young students, mostly from Europe, and some experienced researchers.
The 20th Advanced Course of the Swiss Society for Astrophysics and
Astronomy took place in Les Diablerets from 1 to 6 April 1990. It was
devoted to observational and theoretical aspects of active galactic
nuclei. The previous advanced courses of the Swiss Society for
Astrophysics and Astronomy have regularly taken place in Saas-Fee, a
small resort in the Swiss Alps, hence the name "Saas-Fee" used to de-
scribe the courses and lecture notes. In the last three years, however,
the course was organized in Leysin and in Les Diablerets, both also
situated in the Swiss Alps.