At the beginning of October 1806, the armies of Napoleon were moving towards the Saale, and ere the middle of the month the battles of Auerstadt and Jena were fought and lost. Duke Charles Ferdinand was mortally wounded, and taken back to Braunschweig. A deputation waited on the offended Emperor at Halle, and begged him to allow the aged duke to die in his own house. They were brutally denied by the Emperor, and returned to Braunschweig to try and save the unhappy duke from imprisonment. One evening in the late autumn, Gauss, who lived in the Steinweg (or Causeway), saw an invalid carriage drive slowly out of the castle garden towards the Wendenthor. It contained the wounded duke on his way to Altona, where he died on November 10, 1806, in a small house at Ottensen, 'You will take care,' wrote Zach to Gauss, in 1803, 'that his great name shall also be written on the firmament.'

For a year and a half after the death of the duke Gauss continued in Braunschweig, but his small allowance, and the absence of scientific company made a change desirable. Through Olbers and Heeren he received a call to the directorate of Gottingen University in 1807, and at once accepted it. He took a house near the chemical laboratory, to which he brought his wife and family. The building of the observatory, delayed for want of funds, was finished in 1816, and a year or two later it was fully equipped with instruments.