De Sitter, Willem, << duh SIHT uhr, WIHL uhm >> (1872-1934), was a noted Dutch astronomer. He began his career studying celestial mechanics. Early in his career, De Sitter determined the masses of Jupiter’s moons. He is best known for his realization that Einstein’s general relativity theory might apply to cosmology.
In 1917, De Sitter pointed out that if the universe’s density were low enough, the universe would be expanding at nearly the speed of light. His proposal gained in credibility when American astronomer Edwin Hubble later observed that the farther away distant galaxies are, the faster they seem to be receding. De Sitter was born on May 6, 1872, in Sneek in the Netherlands. He died on Nov. 20, 1934.
