Approximate year of discovery of ejnar hertzsprung

Explanation:

In the period 1911–1913, together with Henry Norris Russell, he developed the Hertzsprung–Russell diagram. In 1913 he determined the distances to several Cepheid variable stars by parallax, and was thus able to calibrate the relationship, discovered by Henrietta Leavitt, between Cepheid period and luminosity.

Ejnar Hertzsprung, (born Oct. 8, 1873, Frederiksberg, near Copenhagen, Den.—died Oct. 21, 1967, Roskilde), D