Wilhelm Julius Foerster (December 16 1832 – January 18 1921) was a German astronomer, father of the pacifist and ethicist Friedrich Wilhelm Foerster . His name can also be written Förster, but is usually written "Foerster" even in most German sources where 'ö' is otherwise used in the text.

Worked as Johann Franz Encke's assistant. Director of the Berlin Observatory from Encke's death in 1865 until 1903.

Co-discovered asteroid 62 Erato with Oskar Lesser, the first co-discovery on record. The asteroid 6771 Foerster is named after him.

Participated in the German Society for Ethical Culture (Deutschen Gesellschaft für ethische Kultur) (in which Albert Einstein also participated) and the German Peace Society (Deutsche Friedensgesellschaft), and resisted the rise in nationalism brought about by the outbreak of World War I.

When 93 German intellectuals signed the Aufruf an die Kulturwelt manifesto in support of the war, Foerster was one of only four intellectuals to sign the Aufruf an die Europäer counter-manifesto (the others were Albert Einstein; the philosopher Otto Buek ; and its author, the physiologist Georg Nicolai ).

His son Friedrich Wilhelm Foerster also participated in the GSEC, along with Georg von Gizycki .