Pieter Oosterhoff

He was the co-administrator, along with Jan Oort, of the Leiden Observatory in the Netherlands.

His published papers are primarily in regard to variable stars and photometry.

He is most noted for his 1939 observation that there appear to be two populations of globular clusters based on the periodicities of their RR Lyrae variable stars.

In 1954 he was one of twelve European astronomers who drafted a statement that would lead to the formation of the ESO.

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