| Astrophysics (index) | about |
An astronomical unit (AU) is a distance unit intended to convey the distance between the Earth and the Sun, or more specifically the mean of the Earth's orbit's aphelion and perihelion. However, it is now fixed at 149597870700 meters, considered a reasonable fixed unit to approximate the Earth-Sun distance. It is commonly used for distances within the solar system and other star systems, e.g., for orbital radii. An AU is equivalent to:
Some distances in AU:
| 0.0026AU | distance from Earth to Moon |
| 0.0093AU | diameter of the Sun |
| 5.2AU | radius of Jupiter's orbit |
| 30AU | radius of Neptune's orbit |
| 276173AU | distance to Alpha Centauri |
| 1.6 billion AU | distance to galactic center |
| 1604 billion AU | distance to Andromeda |