Prussian astronomer Friedrich Wilhelm Bessel recalculated the orbit of comet of Edmund Halley in 1804, used parallax to measure the distance from Earth to the twin star 61 Cygni in 1838, and developed a class of mathematical functions, based on his study of planetary perturbation. Prussian astronomer Friedrich Wilhelm Bessel recalculated the orbit of comet of Edmund Halley in 1804, used parallax to measure the distance from Earth to the twin star 61 Cygni in 1838, and developed a class of mathematical functions, based on his study of planetary perturbation. ...more