The Astronomical Unit

The Distance from Earth to Sun

The astronomical unit, the AU, is a unit of distance equal approximately to the average distance between the earth and sun. More precisely stated, one astronomical unit is approximately the value of the semimajor axis of the orbit of the earth. (For the purists, the AU is actually a tiny bit less than the semimajor axis.) This represents a distance of about 93 million miles or 150 million kilometers.

Expressing a distance in AU then represents a comparison with the earth's distance from the sun. Jupiter at 5.2 AU from the sun is 5.2 times further from the sun than the earth. Pluto at 39.5 AU is almost 40 times farther from the sun than the earth is.

One ly represents a distance of 63,240 AU.  


Copyright © 1998 - 2010 by Arnold V. Lesikar,
Professor Emeritus
Dept. of Physics, Astronomy, and Engineering Science,
St. Cloud State University,St. Cloud, MN 56301-4498

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