how long is an astronomical unit
1 AU = 149,597,870.700 kilometers (or 149,597,870,700 meters). Definition: An Astronomical Unit is the mean distance between the Earth and the Sun.In 2012, the International Astronomical Union defined the distance to be 149,597,870,700 meters. Historical Background: Tycho Brahe estimated the distance between the Sun and the Earth at 8 million kilometers (5 million miles).Later, Johannes Kepler estimated the AU was at 24 million kilometers (15 million miles).n 2012, the International Astronomical Union defined the distance to be 149,597,870,700 meters. Historical Background: Tycho Brahe estimated the distance between the Sun and the Earth at 8 million kilometers (5 million miles). Later, Johannes Kepler estimated the AU was at 24 million kilometers (15 million miles).