Peter Ganzen
GermanyBiography of Peter Andreas Hansen
Peter Andreas Hansen was a renowned German astronomer born in 1795 in Tønder, Schleswig. Despite his passion for mathematics, Hansen was unable to fully devote himself to the study of his favorite subject due to his father's occupation as a goldsmith. He had to pursue his studies sporadically, while also dedicating his free time to learning languages and crafting various scientific instruments.
Unable to continue his beloved pursuits, Hansen apprenticed as a clockmaker in Flensburg in 1818 before moving to Berlin. There, he continued his studies in clockmaking for a year before returning to his hometown and opening his own clock workshop. In 1820, Hansen had the opportunity to travel to Copenhagen to study mathematics and astronomy with Schumacher. From 1821, he became Schumacher's permanent collaborator in Holstein, specializing in degree measurements. In 1825, he was invited to become the director of the Gotha Observatory, succeeding Encke. Hansen remained in Gotha until his death in 1874. During his tenure, he built a new observatory in 1857.
Hansen's outstanding works brought him fame both in Germany and abroad. In 1846, he became a member of the Royal Saxon Society of Sciences, and in 1865, he was elected a member of the Berlin Academy of Sciences. Particularly noteworthy are his works on the theory of perturbations in the motion of planets and comets. His research on the motion of the Moon, presented in "Tables de la Lune, construites d'après le principe Newtonien de la gravitation universelle" published in 1857 and funded by the British government, is still used today. The Sun tables, published by Hansen in collaboration with Olufsen in 1853, were also widely used until recently when they were replaced by more accurate calculations by Leverrier.
In addition to his work on perturbation theory, Hansen also made contributions to the theory of instruments such as the heliometer, equatorial, and transit instrument. He also engaged in geodesy, dioptrics, and the theory of probabilities. Despite being limited to a modest observatory like Gotha's, Hansen introduced various improvements to astronomical instruments. Some of his notable students include astronomers Auwers, Wagner (former vice-director of the Pulkovo Observatory), Gould, Poulakhov, and Tsekh, among others.
