Astronomical unit
| Astronomical unit | |
|---|---|
The grey line indicates the Earth–Sun distance, which on average is about 1 astronomical unit. | |
| General information | |
| Unit system | Astronomical system of units (Accepted for use with the SI) |
| Unit of | length |
| Symbol | au or AU or AU |
| Conversions | |
| 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 1.5813×10−5 ly 215.03 R☉ |
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to 149597870700 m. Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012.
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. One au is approximately equivalent to 499 light-seconds.