Backlund, Jöns Oskar (1846–1916)
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Born in Sweden, worked in Russia, at the Dorpat (now Tartu) Observatory, became director of Pulkovo Observatory, and the Imperial Academy of Sciences in Petrograd. He employed a large staff to compute the orbit of Comet Encke, eventually concluding that the comet's motion was affected by non-gravitational forces (now known to be light pressure and magnetic forces from the Sun).