"Europe Day" is a celebration of Europe held annually on 9 May. 9 May 1950 was the date of the "Schuman Declaration", the proposal to pool the French and West German coal and steel industries. This is considered a founding moment for what is now the EU and was adopted as its flag day at the Milan European Council summit in 1985. For those who like history, here is a link to the full text of the declaration: http://europa.eu/abc/symbols/9-may/decl_en.htm 

The Flag of Europe consists of a circle of twelve golden (yellow) stars on a blue background. The European Union (EU) adopted the flag in the 1980s. However, it was first adopted by the Council of Europe (CoE), which created it in 1955.