Space Facts

Astronomical Unit (AU)

How big is it?

"AU" is a measure of distance based on the radius of Earth's orbit around the sun. It is a distance equal to 149,600,000 km (93,000,000 miles). The distances within a star system, between binary components, and the distances between a star and its planets, for instance, are usually measured in AU's.

Examples:

The following examples show the mean distances in Astronomical Units of the planets from the sun:

• Mercury—0.387
• Venus—0.723
• Earth—1.000
• Mars—1.524
• Jupiter—5.203
• Saturn—9.539
• Uranus—19.182
• Neptune—30.058

For other units used in astronomy for distance measure, compare parsecs and light years.

References:
Astronomy Data Book, by J.H. Robinson & J. Muirden — John Wiley & Sons, New York
A Field Guide to the Stars and Planets, by D.H. Menzel — 1964, Houghton Mifflin Company, Boston