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Astronomical unit (au)

Quantity: Distance · Category: Non-SI

The astronomical unit is the mean distance between Earth and the Sun — about 150 million kilometres. Since 2012 it is fixed by definition, making it an exact conversion to metres.

Relation to SI

1 au = 149,597,870,700 m (exact by definition)

Examples

  • Earth orbits at 1 au from the Sun by definition.
  • Neptune orbits at about 30 au.
  • Voyager 1 is over 160 au from the Sun.