What does an astronomical unit (AU) measure?

An astronomical unit (AU) is defined as the average distance from Earth to the Sun. This unit of measurement is approximately 93 million miles or 150 million kilometers. The use of the AU allows for a simpler way to express distances within our solar system, particularly when discussing the orbits of the planets around the Sun.

This measurement is significant because it provides a standard reference point for understanding the vast distances in space. Since the distance to the Sun can vary slightly depending on Earth's elliptical orbit, the term "average distance" is used to convey that AU is not an exact distance at all times.

The other options do not accurately describe the astronomical unit. For instance, the distance from the Sun to Pluto varies greatly due to its eccentric orbit and is not representative of what an AU measures. Similarly, the average distance across Earth's orbital path would not be correct, as this distance would be larger than the average distance to the Sun itself. Lastly, the distance light travels in ten minutes is a different kind of measurement and does not relate to the standard unit of distance that an AU represents.