Astronomical unit
Symbol: AU
Originally, the AU was defined as the length of the semi-major axis of the Earth's elliptical orbit around the Sun.
Astronomical Union revised the definition in 1976 as the radius of an unperturbed circular Newtonian orbit about the Sun of a particle having infinitesimal mass, moving with a mean motion of 0.017 202 098 95 radians per day. It is approximately equal to the mean Earth-Sun distance.
The astronomical unit is not formally defined within the International System of Units, but often used by astronomers.
1AE = 149,597,870,691m
1m ≈ 0.0000000000066845AE