Astronomical Unit
Astronomical Unit (AU), unit of distance used in the measurement of orbits and trajectories within the solar system . One AU is the average distance between the earth and the sun . Its value has been established as, roughly, 149,600,000 km (92,956,000 mi) by means of radar -ranging studies of nearby celestial objects such as Venus or passing asteroids; these studies have enabled astronomers to determine the scale of the solar system with great accuracy.