The world\'s top astronomical body has endorsed the definition of the \"Astronomical Unit\" (AU), a measurement used to calculate the distance between stars and planets. The AU -- based on the distance between Earth and the Sun -- has long been in use by astronomers, and the decision by the International Astronomical Union (IAU) simply removes a tiny three-metre (10-feet) margin of error. \"Until now, the value in metres of AU was determined experimentally, depending on the models, observations and reference system that was used,\" it said. Officially, the AU is 149,597,870,700 metres (149,597,870.7 kilometres or 92,955,807.273 miles) exactly. The ruling was approved at the IAU\'s general assembly in Beijing from August 20-31, the Paris Observatory said on Friday in a press release.