Semi-major axis: roughly speaking, the mean distance between a body and the object it orbits.
Astronomical Unit: approximately the Earth's semi-major axis.
In this scale model, 1 AU is represented as 1 km.
Each orbit is represented by a circle at the semi-major axis. Real orbits are elliptical.
Mouse over the orbits for more info about each solar system body.
Inspired by a similar model by the University of Manitoba.