Swiss-born US astronomer who studied and classified star clusters found in our Galaxy. He also took part in observational tests of the general theory of relativity 1922.
Trumpler was born in Zürich and studied there and in Germany at Göttingen. In 1915 he moved to the USA; he was professor of astronomy at the University of California from 1930.
At the Allegheny Observatory in Pennsylvania, Trumpler noted that galactic star clusters contain an irregular distribution of different classes of stars, and these observations paved the way for later theories about stellar evolution. In 1930 he showed that interstellar material was responsible for obscuring some light from galaxies, which had led to overestimations of their distances from Earth.
Working at the Lick Observatory, near Chicago, he studied the planet Mars, concluding that some of the supposed 'canals' observed by Italian astronomer Giovanni Schiaparelli could be volcanic faults. Trumpler's hypothesis, made in 1924, did not gain real support until the return of the photographs taken by the Mariner 9 space probe to Mars, more than 50 years later.