astronomical unit

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:

• about 150 million km.
• about 93 million miles.
• 4.848 × 10^-6 parsecs.
• 1.581 × 10^-5 light-years.

Some distances in AU: