in front of the Göttingen Observatory building (1909) Hertzsprung was born in
Frederiksberg, Denmark, the son of Severin and Henriette. He studied chemical engineering at
Copenhagen Polytechnic Institute, graduating in 1898. After spending two years working as a chemist in St. Petersburg, in 1901 he studied
photochemistry at
Leipzig University for a year. His father was an amateur astronomer, which led to Ejnar's interest in the subject. He began making astronomical observations in Frederiksberg in 1902, and within a few years had noticed that stars with similar
spectral type could have widely different
absolute magnitudes. In 1909, he took a position at the
Göttingen Observatory under director
Karl Schwarzschild. In 1911 Hertzsprung developed the
Hertzsprung–Russell diagram, independently developed in 1913 by
Henry Norris Russell. In 1913 Hertzsprung 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. He used the earlier classification system developed by
Antonia Maury in his work. 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 ==