Among his graduate students at Leiden was Gerard Kuiper .
From 1919 to 1946 Hertzsprung worked at Leiden Observatory in the Netherlands , from 1937 as director .
Among Hertzsprung 's graduate students Leiden Observatory Leiden was Gerard Kuiper .
From 1919 to 1946 Hertzsprung worked at Leiden Observatory in the Netherlands , from 1937 as director .