A system of measurement used within our solar system based on the mean distance between the Earth and the Sun 92,957,130 miles (149,600,000 km). The relation of planets and other bodies to the Sun is expressed using the AU as a measuring stick. For example, the mean distance of Saturn from the Sun is 9.54 au; the semimajor axis of the Earth's orbit is 1.000000031 au.
Comments: Astronomical Unit