The astronomical unit (symbol: au, or AU or AU) is a unit of length, roughly the distance from Earth to the Sun and equal to about 150 million kilometres (93 million miles) or ~8 light minutes. The actual distance varies by about 3% as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once each year. The astronomical unit was originally conceived as the average of Earth's aphelion and perihelion; however, since 2012 it has been defined as exactly 149597870700 m (see below for several conversions).
|Unit system||Astronomical system of units|
(Accepted for use with the SI)
|Symbol||au or AU or AU|
|1 au or AU or AU in ...||... is equal to ...|
|metric (SI) units||1.495978707×1011 m|
|imperial & US units||9.2956×107 mi|
|astronomical units|| 4.8481×10−6 pc|
The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec.