The flag of Australia is a national flag. In 1901, Australia became a single country, instead of six separate colonies. A competition was held to design a new flag for the new country. The winning flag has a blue background, the Union Jack, and six stars. Five stars are in the shape of the constellation the Southern Cross, the other is the Commonwealth Star. The flag has been used from 1903, but did not become the official flag of Australia until 1953.