In 1912 his family moved back to the Netherlands where he went to study astronomy at the University of Amsterdam and was the first student to earn his PhD (at the age of 22) with Ejnar Hertzsprung at Leiden University.
His family moved back to the Netherlands. This was in 1912. He went to study astronomy at the University of Amsterdam. He was the first student to earn his PhD (at the age of 22) with Ejnar Hertzsprung at Leiden University.