Peter Andreas Hansen, a German astronomer, born in Tondern, Schleswig, Dec. 8, 1795, died in Gotha, March 28, 1874. He early excelled in astronomical studies, and in 1825 became director of the Seeberg observatory near Gotha. The new observatory in the suburb Erfurt of that town was built under his direction in 1859. He wrote a number of works on the problems of physical astronomy, including geodesy. His Fundamenta nova Investigationis Orbitoe verm, quam Luna peruvstrat (Gotha, 1838), formed the basis on which he subsequently calculated his celebrated Tables de la lune (London, 1857), for which the British government awarded him, on account of their practical value to navigators, a prize of £1,000. In explanation of the methods of calculation which he had employed in computing the perturbations of the moon, given in his tables, he published Darlegung der theoretischen Berechnun-gen der in den Mondtafeln angewiesenen Sto-rungen (Leipsic, 1862-'4). Other works of importance are: Berechnung der absoluten Sto-rungen der Planeten (Leipsic, 1856-'9); Geo-datische Untersuchungen (1865-'8); Tafeln der Egeria (1868); and Die Meinsten Quadrate in Hirer Anwendung anf die Geodasie (1868).