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Rheticus (Georg Joachim von Lauchen) (rā´tēkŏŏs, gā´ôrk yōä´khĬm fən lou´khən), 1514–76, German astronomer, mathematician, and first disciple of Copernicus. In 1540 he printed a summary of heliocentric ideas in the Narratio prima and in 1542 supervised publication of the trigonometric sections of Copernicus's masterpiece De revolutionibus. He subsequently persuaded Copernicus to publish (1543) the entire work. To mathematics he contributed Opus palatinum de triangulis, in which for the first time trigonometric functions were related to angles rather than to the arcs of circles.

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