An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) A unit of length equal to 149 597 870 700 m exactly, with symbol "au" (re-definition at the International Astronomical Union's 28th General Assembly in Beijing, China, August 20-31). The astronomical unit equals 1.5813 × 10^-5 → light-years and 4.8481 ×10^-6 → parsecs.
2) Previous definition: The radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2 π / k days, where k is the → Gaussian gravitational constant. This is slightly less than the semi-major axis of the Earth's orbit.

→ astronomical; → unit.