Named in memory of Peter Andreas Hansen (1795–1874), leading theoretical astronomer of the nineteenth century, at the occasion of the 200th anniversary of his birth. Born in Tondern, Schleswig, he became director of the Seeberg Observatory near Gotha {see planet  (1346)} in 1825. His most important work was the improvement of the theories and tables of the orbits of the principal bodies in the solar system. Hansen’s lunar theory — yielding a very accurate new value of the astronomical unit — was used for the Nautical Almanac until 1922. He invented the method of perturbations in coordinates. Simon Newcomb {see planet  (855)}, who continued his work, considered Hansen the greatest master of celestial mechanics since Laplace {see planet  (4628)}. (M 25229) _ _.