AU
Astronomical Unit
An astronomical unit is a unit of distance roughly equal to the average distance between the Earth and the Sun — approximately 149.6 million kilometers or 93 million miles. It is primarily used to measure distances within our solar system.
History
The astronomical unit has been used since the 17th century when astronomers first calculated the Earth-Sun distance. In 2012, the International Astronomical Union fixed the AU at exactly 149,597,870,700 meters. For example, Mars orbits at about 1.52 AU from the Sun.