Despite this, beaches are packed and experts are growing concerned. As thousands flock to the NSW coastline to enjoy a day in sun, the Bureau of Meteorology's UV index shows levels well into the "extreme" category. Originally developed in Canada, the UV index is a system designed to tell us how much radiation from the sun is reaching us on earth. The spaced out crowd watches on during day five of the Third Test match in the series between Australia and India at Sydney Cricket Ground.(Getty) Once the UV index reaches three, people with fair skin are in danger of getting burnt.