Complex sentence: From 1989 to 1992 he was involved in scientific research at ESO, from 1988 until 1991 he worked on the study of galactic structure with the International Astronomical Union, and from 1990 until 1993 he was president of the Swiss Society for Astrophysics and Astronomy.
Split into simpler sentences: From 1989 to 1992 he was involved in scientific research at ESO, from 1988 until 1991 he worked on the study of galactic structure with the International Astronomical Union. From 1990-93 he was president of the Swiss Society for Astrophysics and Astronomy.