The "Hauptkolloquium" is a formal seminar which is held every week on 11:00 am, Fridays at the MPIfR. It is sponsored by the MPIfR Bonn and the Argelander-Institut für Astronomie der Universität Bonn (AIfA).
Talks are 1hr duration and speakers are invited in order to cover a broad range of astronomical and astrophysical topics. Besides the "Hauptkolloquium" there are also a number of other, similar colloquia which can be scheduled throughout the week (e.g. "Sonderkolloquium").