In 1917 he applied for the École Normale Supérieure and placed first in his class, but he decided to serve in the army during World War I.
As he had held a long interest in astronomy, in 1925 he left his teaching position to join the Paris Observatory.
He also discovered an important error in the period-luminosity law of Cepheid variables, that had resulted in a significant underestimation of the size of the universe.
During World War II he served in the French resistance against Nazi occupation, risking his life on a number of occasions.
Following the war he developed bad health around 1950, and suffered heart and liver problems up until his death.