Colloquium - Jan Hendrik Oort: Master of the Galactic System

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Jan Hendrik Oort (1900--1992) was a giant among twentieth century astronomers. His studies in Groningen under his `groote leermeester’ Kapteyn prompted him to enter the field of statistical astronomy and the dynamics of the Galaxy. His two years at Yale Observatory, where he worked as an observer in the field of latitude variations resulted in a strong interest in `fundamental’ astronomy, in particular the matter of absolute declinations that Kapteyn also had worked on. His study of high-velocity stars eventually led to his discovery of differential Galactic rotation and definition of the Oort constants. This in turn led to applications of Galactic dynamics, an understanding of Kapteyn’s Star Streams, the Oort limit and the stellar distribution in the Galaxy from Kapteyn’s Plan of Selected Areas. Oort worked extensively in the developing field of surface photometry on photographic plates as a first step towards investigating the dynamics of external galaxies. And he worked on the superluminal expansion of Nova Persei.

The second World War was a real watershed, as he described himself as well, radio astronomy being the major, but not only factor in this. He extended his work to the physics of interstellar dust, motions in the interstellar medium, Stellar Populations, the origin of comets and the physics of supernova remnants as the Crab Nebula. Eventually he moved vis high-velocity clouds and the galactic center into the field of large-scale structure of the Universe. Oort was the founder of radio telescopes in Kootwijk, Dwingeloo en Westerbork, en he was a leader in the International Astronomical Union and played a vital role in the second Leiden expedition t Kenya and the development of the leiden Southern Station and was a founder of the European Southern Observatory.

In my talk I will concentrate on the period before WWII and discuss Kapteyn’s influence on Oort, his observational work in the optical at the Yale, Perkins, Mount Wilson and McDonald Observatories, and the superluminal expansions of Nova Persei. If time permits I will discuss his involvement with work on the Crab Nebula.