SCIENCE Transits | The AU | The AU using transit method | The AU using radar

The Astronomical Unit

The Astronomical Unit (usually abbreviated as AU) is the name given to the average distance between the Earth and the Sun. It is actually the distance from the Sun that the Earth would be if it were in a perfectly circular orbit and took precisely 365.2568983 days (a Gaussian year) to orbit. As the Earth's orbit is elliptical, the AU is slightly smaller than the mean distance. Using radar we now know that the AU is 149,597,870 km (about 93 million miles).

In this system of units, Jupiter is 5.2 AU from the Sun and the Moon is 0.0026 AU from the Earth.

Internet Links
Definition of Astronomical Unit (Wikipedia)
Definition of Gaussian year (Wikipedia)
Scale of the Solar System (GSFC/NASA)