For example , in 2009 , the best estimate , as approved by the International Astronomical Union ( IAU ) , was : The relative uncertainty in these measurements is 0.02 parts per billion ( ) , equivalent to the uncertainty in Earth-based measurements of length by interferometry .
s of 2009 [ [ update ] ] , the best estimate , as approved by the International Astronomical Union ( IAU ) , is : The relative uncertainty in these measurements is 0.02 parts per billion ( 2 × 10-11 ) , equivalent to the uncertainty in Earth-based measurements of length by interferometry .