Which Oceanian country's flag features the Southern Cross with four 7-pointed stars and one 5-pointed star? Australia. The Australian flag shows the Southern Cross in its fly half, with four larger seven-pointed stars and a smaller five-pointed star.
The Southern Cross is the constellation Crux Australis, a prominent feature of the southern sky. On Australia's flag, the four larger stars are Alpha, Beta, Gamma, and Delta Crucis; the smaller star is Epsilon Crucis. The flag also includes the Union Jack and a separate seven-pointed Commonwealth Star.
Australia's flag emerged from a 1901 design competition held after federation. The Southern Cross stars were standardised in 1903 so that the four larger stars had seven points and the smallest had five. In 1908, the Commonwealth Star gained its seventh point to represent Australia's territories and future states.
New Zealand is the most common mix-up: its flag also uses the Southern Cross, but its four stars are red and five-pointed. Counting the points distinguishes the two designs immediately.