Johann Gottfried Galle ( June 9 , 1812 in Radis , Saxony-Anhalt -- July 10 , 1910 in Potsdam , Brandenburg ) was a German astronomer at the Berlin Observatory who , with the help of student Heinrich Louis d'Arrest , was the first person to view the planet Neptune , and know what he was looking at ( September 23 , 1846 ) . Johann Gottfried Galle ( 9 June 1812 â `` 10 July 1910 ) was a German astronomer at the Berlin Observatory who , with the assistance of student Heinrich Louis d'Arrest , was the first person to view the planet Neptune , and know what he was looking at , on 23 September , 1846 .