Ejnar Hertzsprung

Ejnar Hertzsprung (; 8 October 1873 – 21 October 1967) was a Danish chemist and astronomer born in Copenhagen.  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.  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.  Among his graduate students at Leiden was Gerard Kuiper. 

Perhaps his greatest contribution to astronomy was the development of a classification system for stars to divide them by spectral type, stage in their development, and luminosity.  The so-called "Hertzsprung–Russell Diagram" has been used ever since as a classification system to explain stellar types and stellar evolution.  He also discovered two asteroids, one of which is 1627 Ivar, an Amor asteroid. 

His wife Henrietta (1881–1956) was a daughter of the Dutch astronomer Jacobus Kapteyn.  Hertzsprung died in Roskilde in 1967.  The asteroid 1693 Hertzsprung was named in his honour. 

Asteroids discovered 
 1627 Ivar (25 September 1929)
 1702 Kalahari (7 July 1924)

Honors 

 Awards
 Gold Medal of the Royal Astronomical Society in 1929
 Bruce Medal in 1937

 Named after him
 lunar impact crater Hertzsprung
 main-belt asteroid 1693 Hertzsprung

Sources 
 Sky & Telescope, January, 1968, Sky Publishing Corporation, Cambridge

References

External links 
 Bruce Medal page
 Awarding of Bruce Medal: PASP 49 (1937) 65
 Awarding of RAS gold medal: MNRAS 89 (1929) 404

Category:1873 births
Category:1967 deaths
Category:20th-century astronomers
Category:People from Copenhagen
Category:Danish astronomers
Category:Danish chemists
Category:Discoverers of asteroids
Category:Recipients of the Gold Medal of the Royal Astronomical Society