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The flag of Australia is based on the British maritime Blue Ensign – a blue field with the United Kingdom flag (Union Jack) in the canton or upper hoist quarter – augmented with a large white seven-pointed star (the Commonwealth Star) and a representation of the Southern Cross constellation, made up of five white stars – one small five-pointed star and four, larger, seven-pointed stars. There are other official flags representing Australia, its people and core functions of government. The flag's original design (with a six-pointed Commonwealth Star) was chosen in 1901 from entries in a competition held following Federation, and was first flown in Melbourne on 3 September 1901, the date proclaimed as Australian National Flag Day. A slightly different design was approved by King Edward VII in 1903. The current seven-pointed Commonwealth Star version was introduced by a proclamation dated 8 December 1908. The dimensions were formally gazetted in 1934, and in 1954 the flag became recognised by, and legally defined in, the Flags Act 1953, as the "Australian National Flag".

Source: Wikipedia