The astronomical unit (symbol: au, ua, or AU) is a unit of length, roughly the distance from Earth to the Sun. However, that distance varies as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year. Originally conceived as the average of Earth 's aphelion and perihelion, since 2012 it has been defined as exactly 7011149597870700000 ♠ 149 597 870 700 metres or about 150 million kilometres (93 million miles). The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. However, it is also a fundamental component in the definition of another unit of astronomical length, the parsec.
the mean distance between the earth and the sun is called the
astronomical unit astronomical unit