In the period 1911-1913 with Henry Norris Russell, he developed the Hertzsprung-Russell diagram.
In 1913 he determined the distances to several Galactic Cepheid stars by statistical parallax, and was thus able to calibrate the relationship discovered by Henrietta Leavitt between Cepheid period and luminosity. In this determination he made a mistake, possibly a slip of the pen, putting the stars 10 times too close. He used this relationship to estimate the distance to the Small Magellanic Cloud.
From 1919 to 1946 Hertzsprung worked at Leiden Observatory in The Netherlands, from 1937 as director.
He discovered two asteroids, one of which is the Amor asteroid 1627 Ivar.
Asteroids discovered: 2 1627 Ivar September 25, 1929
1702 Kalahari July 7, 1924
* Gold Medal of the Royal Astronomical Society in 1929
* Bruce Medal in 1937.
Named for him
* Hertzsprung crater on the Moon.
* Asteroid 1693 Hertzsprung.
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