PETER ANDREAS

See also:

• PETER ANDREAS HANSEN (1795-1874)

HANSEN (1795-1874)  , Danish astronomer, was born on the 8th of December 1795, at Tondern, in the duchy of Schleswig . The son of a goldsmith, he learned the trade of a watchmaker at Flensburg, and exercised it at Berlin and Tondern, 1818-182o . He had, however, long been a student of science; and Dr Dircks, a physician practising at Tondern, prevailed with his father to send him in 1820 to Copenhagen, where he won the patronage of H . C . Schumacher, and attracted the personal notice of King Frederick VI . The Danish survey was then in progress, and he acted as Schumacher's assistant in work connected with it, chiefly at the new observatory of Altona, 1821-1825 . Thence he passed on to Gotha as director of the Seeberg observatory; nor could he be tempted to relinquish the post by successive invitations to replace F . G . W . Struve at Dorpat in 1829, and F . W . Bessel at Konigsberg in 1847 .

The problems of gravitational

astronomy engaged the chief part of Hansen's attention . A research into the mutual perturbations of Jupiter and Saturn secured for him the prize of the Berlin Academy in 183o, and a memoir on cometary disturbances was crowned by the Paris Academy in 185o . In 1838 he published a revision of the lunar theory, entitled Fundamenta nova investigationis, &c., and the improved Tables of the Moon based upon it were printed in 1857, at the expense of the British government, their merit being further recognized by a grant of £1000, and by their immediate adoption in the Nautical Almanac, and other Ephemerides . A theoretical discussion of the disturbances embodied in them (still familiarly known to lunar experts as the Darlegung) appeared in the Abhandlungen of the Saxon Academy of Sciences in 1862–1864 . Hansen twice visited England and was twice (in 1842 and 186o) the recipient of the Royal Astronomical Society's gold medal . He communicated to that society in 1847 an able paper on a long-period lunar inequality (Memoirs Roy . Asir . Society, xvi . 465), and in 1854 one on the moon's figure, advocating the mistaken hypothesis of its deformation by a huge elevation directed towards the earth (lb. xxiv . 29) . He was awarded the Copley medal by the Royal Society in 185o, and his Solar Tables, compiled with the assistance of Christian Olufsen, appeared in 1854 . Hansen gave in 1854 the first intimation that the accepted distance of the sun was too great by some millions of miles (Month .

Notices Roy . Asir .

Soc. xv . 9), the error of J . F . Encke's result having been rendered evident through his investigation of a lunar inequality . He died on the 28th of March 1874, at the new observatory in the town of Gotha, erected under his care in 1857 . See Vierteljahrsschrift astr . Gesellschaft, x . 133; Month . Notices Roy . Asir .

Society,

xxxv . 168; Proc . Roy . Society, xxv. p. v.; R . Wolf, Geschichte der Astronomic, p . 526; Wochenschrift fur Astra' nomie, xvii . 207 (account of early years by E . Heis) ; Allgemeine deutsche Biographie (C . Bruhns) . (A . M .