AU: The astronomical unit, or AU, is a measure of length. It is equal to the average distance between the Earth and the Sun. This distance is about 93,500,000 miles. So, the Earth is 1 AU, or 93,500,000 miles from the Sun. It is often used to describe the distances between the Sun and the other objects in the solar system. For example, Pluto's average distance from the Sun is 39.5 AU. That means Pluto is 39.5 times farther from the Sun than Earth is.
