1873-1967

Danish Astronomer

Ejnar Hertzsprung introduced the concept of absolute magnitude, the intrinsic brightness of a star. He worked out the relationship between a star's brightness and its color (which indicates its surface temperature) at different stages in its evolution. The American astronomer Henry Russell (1877-1957) independently arrived at this relationship a few years later, and was the first to publish it in the form of a diagram. Hertzsprung-Russell diagrams, as they came to be called, are still among the standard tools of astronomy. They are used to provide insights into the changes in individual stars over time, as well as to characterize populations of stars.

Hertzsprung was born in Frederiksberg, Denmark, near Copenhagen, on October 8, 1873. He was trained as a chemical engineer at the Frederiksberg Polytechnic, and spent a few years working in Russia. He came to astronomy indirectly, through his interest in photography. In...