# Definition:Astronomical Unit

## Definition

The astronomical unit is a derived unit of length.

It is defined as being $149 \, 597 \, 870 \, 700$ metres.

The astronomical unit is the standard unit of measurement used by astronomers when discussing distances within the solar system.

It is derived as the approximate mean distance from the Earth to the Sun.

### Approximate Values

The astronomical unit is approximately $150 \, 000 \, 000 \, \mathrm {k m}$, or $93$ million (international) miles.

### Symbol

There are a number of symbols which are in use for the astronomical unit:

$\mathrm {AU}$
$\mathrm {au}$
$\mathrm {ua}$