US astronomer who was the first to put in graphic form what
became known as the Hertzsprung-Russell diagram 1913.
Russell was born in Oyster Bay, New York, and studied at Princeton,
where in 1905 he was made professor and director of the observatory.
In 1921 he moved to the Mount Wilson Observatory, California.
Like Ejnar Hertzsprung, Russell concluded that stars could be grouped
in two main classes, one much brighter than the other. He used Annie
Cannon's system of spectral classification, which also indicated surface
temperature. Most of the stars were grouped together in what became
known as the 'main sequence', but there was a group of very bright stars
outside the main sequence. Russell put forward the theory that all stars
progress at one time or another either up or down the main sequence,
depending on whether they are contracting (and therefore becoming hotter)
or expanding (thus cooling), but the progression he proposed was discredited
within a decade.
Russell's lifelong study of binary stars resulted in a method for calculating
the mass of each star from a study of its orbital behaviour. He pioneered
a system using both orbits and masses in order to compute distance from